CONVECTIVE WEATHER RESEARCH

Brown, R. A., J. M. Kurdzo, P. L. Heinselman, 2009: Progress report on evolutionary characteristics of a tornadic supercell thunderstorm: Comparisons of 1.0–min phased array radar and 4.2–min WSR–88D measurements. Preprints, 25th International Conference on Interactive Information and Processing Systems, Phoenix, AZ, USA, American Meteorological Society, 9B.3.

Brown, R. A., 2009: Considering the problem of having too many WSR–88D volume coverage patterns. Task 5, FY 2009 Memo. of Understanding between NWS Radar Operations Center and NSSL Final Report, 11 pp.

Wicker, L. J., 2009: A two-step Adams-Bashforth-Moulton split-explicit integrator for compressible atmospheric models.. Monthly Weather Review, 137, 3588-3595.

Split-explicit integration methods used for the compressible Navier-Stokes equations are now used in a wide variety of numerical models ranging from high-resolution local models to convection-permitting climate simulations. Models are now including more sophisticated and complicated physical processes, such as multi-moment microphysics parameterizations, electrification, and dry/aqueous chemistry. A wider range of simulations problems combined with the increasing physics complexity may place a tighter constraint on the model's time step compared to the fluid flow's courant number, e.g., the choice of the integration time step based solely on advective courant number considerations may generate unacceptable errors associated from the parameterization schemes. The third-order multistage Runge-Kutta scheme has been very successful as the a split-explicit integration method, however, its efficiency arises partially in its ability to use a time step that is 20–40% larger than more traditional integration schemes. In applications where the time step is constrained by other considerations, alternative integration schemes may be more efficient. Here a two-step third-order Adams-Bashforth-Moulton integrator is stably split in a similar manner as the split Runge-Kutta scheme. For applications where the large time step is not constrained by the advective courant number it requires less computational effort. Stability is demonstrated through eigenvalue analysis of the linear coupled one-dimensional velocity-pressure equations, and full two-dimensional nonlinear solutions from a standard test problem are shown to demonstrate solution accuracy and efficiency.

Wood, V. T., R. A. Brown, D. C. Dowell, 2009: Simulated WSR-88D Velocity and Reflectivity Signatures of Numerically Modeled Tornadoes. Journal of Atmospheric and Oceanic Technology, 26, 876-893.

Low-altitude radar reflectivity measurements of tornadoes sometimes reveal a donut-shaped signature (low-reflectivity eye surrounded by a high-reflectivity annulus) and at other times reveal a high-reflectivity knob associated with the tornado. The differences appear to be due to such factors as (i) the radar’s sampling resolution, (ii) the presence or absence of lofted debris and a low-reflectivity eye, (iii) whether measurements were made within the lowest few hundred meters where centrifuged hydrometeors and smaller debris particles were recycled back into the tornadic circulation, and (iv) the presence or absence of multiple vortices in the parent tornado.

To explore the influences of some of these various factors on radar reflectivity and Doppler velocity signatures, a high-resolution tornado numerical model was used that incorporated the centrifuging of hydrometeors. A model reflectivity field was computed from the resulting concentration of hydrometeors. Then, the model reflectivity and velocity fields were scanned by a simulated Weather Surveillance Radar-1988 Doppler (WSR-88D) using both the legacy resolution and the new super-resolution sampling. Super-resolution reflectivity and Doppler velocity data are displayed at 0.5° instead of 1.0° azimuthal sampling intervals and reflectivity data are displayed at 0.25-km instead of 1.0-km range intervals.

Since a mean Doppler velocity value is the reflectivity-weighted mean of the radial motion of all the radar scatterers within a radar beam, a nonuniform distribution of scatterers produces a different mean Doppler velocity value than does a uniform distribution of scatterers. Nonuniform reflectivities within the effective resolution volume of the radar beam can bias the indicated size and strength of the tornado’s core region within the radius of the peak tangential velocities. As shown in the simulation results, the Doppler-indicated radius of the peak wind underestimates the true radius and true peak tangential velocity when the effective beamwidth is less than the tornado’s core diameter and there is a weak-reflectivity eye at the center of the tornado. As the beam becomes significantly wider than the tornado’s core diameter with increasing range, the peaks of the Doppler velocity profiles continue to decrease in magnitude but overestimate the tornado’s true radius. With increasing range from the radar, the prominence of the weak-reflectivity eye at the center of the tornado is progressively lessened until it finally disappears. As to be expected, the Doppler velocity signatures and reflectivity eye signatures were more prominent and stronger with super-resolution sampling than those with legacy-resolution sampling.

Wood, V. T., L. W. White, 2009: A Skirted Rankine Combined Vortex Model. Extended Abstracts, 24th Conference on Severe Local Storms, Savannah, GA, USA, AMS, P3.4.

Wood, V. T., J. N. Chrisman, 2009: Impacts of the Automated Volume Scan Evaluation and Termination (AVSET) on the WSR-88D Velocity-Azimuth Display (VAD) Wind Profile (VWP). Extended Abstracts, 34th Conference on Radar Meteorology, Williamsburg, VA, USA, American Meteorological Society, P4.1.

Wood, V. T., 2009: Impacts of the automated volume scan evaluation and termination (AVSET) algorithm on the WSR-88D Velocity-Azimuth Display (VAD) Wind Profile (VWP). FY 2009 Memorandum of Understanding Between WSR-88D Radar Operations Center and National Severe Storms Laboratory Task 8.0, 81 pp.

Brown, R. A., 2008: The forecaster’s dilemma: Which WSR–88D VCP to use. Task 5, FY 2008 Memo. of Understanding between NWS Radar Operations Center and NSSL, Final Report, 21 pp.

Brown, R. A., 2008: Statistics of WSR–88D velocity dealiasing errors categorized by VCP, 2005–2008. Task 9, FY 2008 Memo. of Understanding between NWS Radar Operations Center and NSSL, Final Report, 7 pp.

Brown, R. A., V. T. Wood, D. C. Dowell, 2008: Impact of a tornado’s low–reflectivity eye on distorting the associated peak Doppler velocity measurements: A simulation study. Preprints, 24th Conference on Severe Local Storms, Savannah, GA, USA, American Meteorological Society, P3.5.

Burgess, D. W., T. D. Crum, R. J. Vogt, 2008: Impact of wind farms on WSR-88D radars. Extended Abstracts, 24rd Conference on Interactive Information Processing Systems (IIPS), New Orleans, LA, USA, AMS, CD-ROM, bB.3.

Burgess, D. W., 2008: An Aircraft Penetration Through a Rear-Flank Downdraft: Revisiting an old case.. Extended Abstracts, 24th Conf. on Severe Local Storms, Savannah, GA, USA, American Meteorological Society, 4.2.

MacGorman, D. R., W. D. Rust, T. J. Schuur, M. I. Biggerstaff, J. M. Straka, C. L. Ziegler, E. R. Mansell, E. C. Bruning, K. M. Kuhlman, N. R. Lund, N. S. Biermann, C. Payne, L. D. Carey, P. R. Krehbiel, W. Rison, K. B. Eack, W. H. Beasley, 2008: TELEX: The Thunderstorm Electrification and Lightning Experiment. Bulletin of the American Meteorological Society, 89, 997-1013.

The field program of the Thunderstorm Electrification and Lightning Experiment (TELEX) took place in central Oklahoma, May–June 2003 and 2004. It aimed to improve understanding of the interrelationships among microphysics, kinematics, electrification, and lightning in a broad spectrum of storms, particularly squall lines and storms whose electrical structure is inverted from the usual vertical polarity. The field program was built around two permanent facilities: the KOUN polarimetric radar and the Oklahoma Lightning Mapping Array. In addition, balloon-borne electric-field meters and radiosondes were launched together from a mobile laboratory to measure electric fields, winds, and standard thermodynamic parameters inside storms. In 2004, two mobile C-band Doppler radars provided high-resolution coordinated volume scans, and another mobile facility provided the environmental soundings required for modeling studies. Data were obtained from twenty-two storm episodes, including several small isolated thunderstorms, mesoscale convective systems, and supercell storms. Examples are presented from three storms. A heavy-precipitation supercell storm on 29 May 2004 produced greater than 3 flashes per second for 1.5 h. Holes in the lightning density formed and dissipated sequentially in the very strong updraft and bounded weak echo region of the mesocyclone. In a small squall line on 19 June 2004, most lightning flashes in the stratiform region were initiated in or near strong updrafts in the convective line and involved positive charge in the upper part of the radar bright band. In a small thunderstorm on 29 June 2004, lightning activity began as polarimetric signatures of graupel first appeared near lightning initiation regions.

Available online at ://http://ams.allenpress.com/archive/1520-0477/89/7/pdf/i1520-0477-89-7-997.pdf.

MacGorman, D. R., K. M. Kuhlman, E. C. Bruning, W. D. Rust, P. R. Krehbiel, M. I. Biggerstaff, 2008: Small, continual lightning activity in the overshooting turret of supercell storms. Proc. 3rd Annual Conference on Applications of Lightning Data, New Orleans, LA, USA, American Meteorological Society, 4.7.

Several supercell storms have occurred within the region in which the Oklahoma Lightning Mapping Array (OKLMA) maps all three spatial dimensions of lightning. These storms span much of the supercell spectrum -- from non-tornadic storms to storms that produced strong tornadoes and from low-precipitation to heavy-precipitation morphologies. As noted by several studies, supercell storms tend to have much larger flash rates than ordinary isolated thunderstorms; maximum rates are typically hundreds of flashes per minute, even when considering only flashes that produce at least ten mapped points per flash. However, the OKLMA indicates that most of the flashes occurring within the main body of the storm during periods of high flash rates have quite small spatial extents, many with a long dimension of 5 km or less. Not usually included in these flash rates are a large number that appear to be isolated points (sometimes called singletons), each failing criteria of distance or time for associating it with other points in a flash. Often determining whether these isolated points are artifacts of the OKLMA is difficult, but in the overshooting top, they present a coherent pattern that appears plausible. They are distributed throughout a cap having horizontal dimensions comparable to that of the overshooting top and sitting near or on the upper surface. They occur continually, though they are too far apart in time or space to be associated in a flash with each other. A comparison with high-resolution reflectivity data for one storm observed by the two mobile 5-cm wavelength SMART-R radars shows that these isolated points were most concentrated near the top of the 40 dBZ echo in the overshooting turret, but some occurred higher, in regions of small reflectivity or just above the overshooting top. These points may be similar to the continual lightning noted by Bill Taylor in the upper region of a severe storm in the early 1980s.

Available online at ://http://www.ametsoc.org.

MacGorman, D. R., T. Mansell, C. Ziegler, J. Straka, 2008: Detailed storm simulations by a numerical cloud model with electrification and lightning parameterizations. Preprints, 20th International Lightning Detection Conference, Tucson, AZ, USA, Vaisala, 28.

We have further developed our three-dimensional cloud model, which includes parameterizations of lightning, corona from ground, ion production and capture, and inductive and noninductive electrification mechanisms, as well as advanced treatments of advection, microphysics, and dynamics. Our most recent improvements have been to improve the model's treatment of microphysics, particularly particle size distributions. This model has been used to simulate many types of storms, from small isolated storms to extensive storm systems, supercell storms, and an idealized hurricane, with excellent similitude to observed kinematic structure in many cases. We will show examples of our simulations and will discuss relationships among the model fields, particularly between lightning and other storm properties. Lightning usually is correlated with precipitation ice mass and with the mass flux through the mixed phase region for updrafts >10 m/s.

MacGorman, D., K. Kuhlman, W. D. Rust, M. Biggerstaff, P. Krehbiel, B. Rison, 2008: Lightning and electrical structure of a heavy-precipitation supercell storm during TELEX. Preprints, 2nd International Lightning Meteorology Conference, Tucson, AZ, USA, Vaisala, 10.

The Thunderstorm Electrification and Lightning Experiment (TELEX) observed a heavy-precipitation (HP) supercell storm in central Oklahoma on 29 May 2004. In a HP supercell storm, the initial location of the mesocyclone, which is the parent rotation of tornadoes, is embedded well within the precipitation of the storm, instead of being on the edge of the storm(as in classic and low-precipitation supercell storms). Two 5-cm wavelength mobile Doppler radars were positioned near the storm and collected volume scans every 3 minutes for 3 h beginning as the storm became supercellular. The storm had supercell characteristics for this entire period. The Oklahoma Lightning Mapping Array provided three-dimensional data throughout the storm’s supercellular stage and provided two-dimensional data from the time of storm initiation in western Oklahoma. A 10-cm wavelength polarimetric radar also provided data for much of this period.
Lightning flash rates became extraordinarily large as the storm evolved into a supercell and its motion turned rightward. Flash rates increased again (to an estimated peak value of almost 500 flashes per minute) shortly before the storm produced a tornado rated F2 on the Fujita scale. During this period, an upward pulse in lightning density extended as high as 18 km MSL in a plume extending above the equilibrium level. Most flashes in the main body of the storm had small spatial extent (3-10 km). Lightning in the overshooting top consisted of continual single-point flashes.
The region of lightning activity pulsed eastward far into the anvil, up to 100 km from the convective core. Up to 5 -CG flashes per minute were initiated in the anvil more than 40 km from the main storm core, and typically came to ground within a few kilometers horizontally of the location of initiation. Because these -CG strikes occur far from the deep convection, they pose a generally unexpected danger to personnel.
A series of minimums in the plan projection of lightning density (i.e., lightning holes) formed just above the bounded weak echo region. A dual-Doppler synthesis of wind during one volume scan shows the lightning hole was co-located with large vertical wind speeds in the rotating updraft. The hole apparently occurred because precipitation particles had little time to grow and gain charge in the strong updraft before they were lifted to upper regions of the storm and advected outward by flow from the diverging updraft. Lightning mapping data suggest that the vertical polarity of the storm’s electrical structure was inverted from the usual polarity, and this appears to be why CG flashes that began in the anvil were -CG flashes.

MacGorman, D., T. Schuur, M. Kumjian, 2008: Total lightning activity during the re-intensification of Tropical Storm Erin over Oklahoma on 18–19 August 2007. Preprints, 24th Conference on Severe Local Storms, Savannah, GA, USA, American Meteorological Society, 7A.5.

The remnants of Tropical Storm Erin made landfall on the Texas coast on 16 August 2007 and reached Oklahoma on 18 August, where it produced tornadoes, severe straight-line winds, and flooding. In west-central Oklahoma (roughly 800 km from the coast), the system re-intensified and formed an eye and rainband structure characteristic of tropical cyclones. The Oklahoma Mesonet indicated that the system eventually produced greater sustained winds (26 m s-1, 58 mph) and a lower central pressure (1001.3 hPa) than it had produced over open water.

The eye, which fluctuated from 5 to 25 km in diameter, was first apparent on lightning and radar displays at 4:50 am local time and began dissipating over Oklahoma City at 9:50 am. Throughout the period during which the eye formed and dissipated, the eye and the majority of the area of rainbands were well within the region in which the Oklahoma Lightning Mapping Array maps lightning in three dimensions and in which the KOUN S-Band radar provides polarimetric data. Both radar displays and displays of lightning density delineated the formation of the eye and rainband well. Convection extended highest and lightning rates were greatest in the rainband on the southeast flank. The height of convection in the rainband decreased as one approached the eye, and the decrease in height extended around the eye as the eye formed. Some long, horizontal flashes extended eastward from storms along the east side of the eye into the region of widespread light precipitation east of the rainband. The appearance of these long horizontal flashes was similar to the lightning structure observed in the stratiform precipitation regions of mesoscale convective systems. As the cyclone structure weakened, convection on the west side of the eye dissipated, and the remnants of the rainband on the east side propagated eastward as a line of storms.

Though the lightning in this system was probably influenced by being over land, this case still may provide clues to what happens electrically in tropical cyclones over open water, where continuous observations of total lightning activity during tropical cyclone intensification and dissipation are not yet available.

Available online at ://http://www.ametsoc.org.

Rabin, R. M., J. Hanna, 2008: GOES winter precipitation efficiency algorithm.. Extended Abstracts, Fifth GOES Users Conference, 88th AMS meeting, New Orleans, LA, USA, AMS, P1.34.

Wood, V. T., 2008: Improvement of WSR-88D VAD Winds: Cyclonic Wind Fields. Preprints, 28th Conference on Hurricanes and Tropical Meteorology, Orlando, FL, USA, AMS, P2B.3. [Available from Vincent T. Wood, 120 David L. Boren Blvd., National Severe Storms Laboratory, Norman, OK, USA, 73072.]

Hurricanes pose a serious threat to life and property along the Gulf and Atlantic coastal regions of the United States. The WSR-88D network provides the potential to improve hurricane forecasts and warnings by monitoring changes in a hurricane’s track, eye diameter, radar eyewall and rainband reflectivities. The WSR-88D Velocity-Azimuth Display (VAD) Wind Profile (VWP) display is a useful tool for diagnosis of wind fields at different altitudes as a hurricane is approaching a coastal WSR-88D.

The causes of missing winds on the VWP display were related to cyclonic flow from the approaching hurricane. The missing data arose because the extreme positive and negative Doppler velocity values around the VAD circle were inherently not 180 degrees apart and, therefore, the first-harmonic Fourier sine curve used in the operational WSR-88D VAD algorithm was a poor fit to the data. This resulted in root-mean-square (RMS) differences that exceeded the threshold value. In this situation, most of the winds on the VWP display were set equal to missing in spite of the fact that there were strong radar returns.

A new solution to recover or improve VAD winds has been developed. A higher-order polynomial regression technique employs least-squares fit of the Doppler velocity data distributed on the VAD circle. Wind speed is computed from the average of the magnitudes of the positive and negative peaks of the quasi-sine curve. Wind direction is determined from the average of the magnitudes of maximum and minimum azimuths (at which positive and negative Doppler velocity peaks occur, respectively) minus ninety degrees. After applying the experimental technique to a couple of hurricane cases such as Hurricane Katrina (29 August 2005) and Hurricane Rita (20 September 2005), the technique examines a standard deviation about a regression line which agrees well with the RMS value. The higher-order polynomial regression VAD curve fits the measurements with low RMS difference values. It is indicated that the technique does a good job of fitting the curve to the data points with low RMS difference between the curve and data points.

Wood, V. T., L. W. White, 2008: A Skirted Rankine Combined Vortex Model. Extended Abstracts, 24th Conference on Severe Local Storms, Savannah, GA, USA, American Meteorological Society, P3.4.

Wood, V. T., 2008: Need for Potential VAD Improvements. Final Report, FY2008 Memorandom of Understanding Between WSR-88D Radar Operations Center and National Severe Storms Laboratory Task No. 8.1, 76 pp.

Brown, R. A., T. A. Niziol, N. R. Donaldson, P. I. Joe, V. T. Wood, 2007: Improved Detection Using Negative Elevation Angles for Mountaintop WSR-88Ds. Part III: Simulations of Shallow Convective Activity Over and Around Lake Ontario. Weather and Forecasting, 22, 839-852.

During the winter, lake-effect snowstorms that form over Lake Ontario represent a significant weather hazard for the populace around the lake. These storms, which typically are only 2 km deep, frequently can produce narrow swaths (20–50 km wide) of heavy snowfall (2–5+ cm/hr) that extend 50–75 km inland over populated areas. Subtle changes in the low-altitude flow direction can make the difference between accumulations that last for 1–2 hr and accumulations that last 24 hr or more at a given location. Therefore, it is vital that radars surrounding the lake are able to detect the presence and strength of these shallow storms.
Starting in 2002, the Canadian operational radars on the northern side of the lake at King City, ON (WKR) and Franktown, ON (XFT) began using elevation angles as low as -0.1 deg and 0.0 deg, respectively, during the winter to more accurately estimate snowfall rates at the surface. Meanwhile, WSR-88D radars in New York State on the southern and eastern sides of the lake—Buffalo (KBUF), Binghamton (KBGM), and Montague (KTYX)—all operate at 0.5 deg and above. KTYX is located on a plateau that overlooks the lake from the east at a height of 0.5 km. With its upward-pointing radar beams, KTYX’s detection of shallow lake-effect snowstorms is limited to the eastern quarter of the lake and surrounding terrain.
The purpose of this paper is to show—through simulations—the dramatic increase in snowstorm coverage that would be possible if KTYX were able to scan downward toward the lake’s surface. Furthermore, if KBUF and KBGM were to scan as low as 0.2 deg, detection of at least the upper portions of lake-effect storms over Lake Ontario and all of the surrounding land area by the five radars would be complete. Over-lake coverage in the lower half (0-1 km) of the typical lake-effect snowstorm would increase from about 40% to about 85%, resulting in better estimates of snowfall rates in landfalling snowbands over a much broader area.

Brown, R. A., V. T. Wood, cited 2007: A Guide for Interpreting Doppler Velocity Patterns: Northern Hemisphere Edition, 2nd ed.. [Available online at ://http://www.nssl.noaa.gov/papers/dopplerguide/.]

Brown, R. A., R. M. Steadham, 2007: Developing site-specific scanning strategies for WSR-88Ds: Important considerations. Preprints, Annual Meeting, Reno, NV, USA, National Weather Association, 94-95.

Brown, R. A., 2007: Using mesocyclone signatures to compare techniques for creating 1.0 deg azimuthal WSR-88D data from 0.5 deg super-resolution data. Task 3, FY 2007 Memo. of Understanding between NWS Radar Operations Center and NSSL, Final Report, 16 pp.

Brown, R. A., V. T. Wood, 2007: Comparisons of switching from WSR-88D clear air mode to precipitation mode using the operational mode selection function (MSF) and a modified mode selection function (MMSF). Task 4, FY 2007 Memo. of Understanding between NWS Radar Operations Center and NSSL, Final Report, 9 pp.

Burgess, D. W., T. Crum, R. J. Vogt, 2007: Impacts of wind turbine farms on WSR-88D radars. Preprints, 33rd Int. Conf. on Radar Meteor., 6-10 August, 2007, Cairns, Australia, AMS, CD-ROM, 13B.6.

Elmore, K. L., K. A. Scharfenberg, C. Legett, 2007: The NSSL winter hydrometeor classification ground truth program: Public involvement in science. Preprints, 31st Intl. Conf. on Radar Meteor., Cairns, Australia, Amer. Meteor. Soc., CD-ROM, P10.9.

During the winter of 2006-2007, a concerted effort was made by the National Severe Storms Laboratory to collect polarimetric radar data using the KOUN radar during winter precipitation events. Simultaneously, observations of precipitation type within a radius of 150 km of KOUN were solicited from the public. Public response has resulted in about 2500 individual observations of winter precipitation type over the course of three major events. These data are intended to be used to both verify the current hydrometeor classification algorithm performance in winter weather events, and to enhance the algorithm's performance. This paper discusses the nature of the ground truth data collected, its overall utility, the nature and scope of quality assurance checking, how event timing affects observation availability, how best to solicit and encourage public participation, and examples of how the data are being used.

MacGorman, D. R., T. Filiaggi, R. L. Holle, R. A. Brown, 2007: Negative Cloud-to-Ground Lightning Flash Rates Relative to VIL, Maximum Reflectivity, Cell Height, and Cell Isolation. Journal of Lightning Research, 1, 132-147.

This study relates storm cell parameters derived automatically from the Doppler radars of the United States National Weather Service to negative cloud-to-ground lightning activity detected by the United States National Lightning Detection Network. Data from the central United States were processed for over 1200 cells from seventeen days. Each cell’s maximum ground flash rate was compared to a subjective rating of the degree of cell isolation and to three radar-derived cell parameters: maximum reflectivity, maximum vertically integrated liquid (VIL), and the maximum vertical thickness having at least 30 dBZ reflectivity above the 0 deg C isotherm (similar to 30-dBZ cell height). Of the three parameters, the maximum 30-dBZ thickness of cells had the most useful relationship: The mean and modal values of ground flash rates increased with increasing 30-dBZ thickness, and the mean and modal values of 30-dBZ thickness increased with increasing flash rates. However, large ground flash rates provided a better diagnostic for large 30-dBZ thickness than large 30-dBZ thickness provided for large ground flash rates. The degree of cell isolation and the complexity of cell evolution also had a large effect: Cells which were less isolated or whose evolution was more complex were more likely to produce a ground flash and larger ground flash rates. Besides effects of storm complexity and size suggested by previous investigators, we suggest that the more complex charge distribution produced by having older cells nearby improves a cell’s probability of access to the lower positive charge typically needed to initiate negative ground flashes.

MacGorman, D., K. Kuhlman, D. Rust, M. Biggerstaff, T. Schuur, J. Straka, P. Krehbiel, B. Rison, L. Carey, 2007: Lightning and electrical structure of a heavy-precipitation supercell storm during TELEX. Preprints, 13th International Conference on Atmospheric Electricity, Beijing, China, IUGG/Commission on Atmospheric Electricity, OS5-1.

The Thunderstorm Electrification and Lightning Experiment (TELEX) observed a heavy-precipitation (HP) supercell storm in central Oklahoma on 29 May 2004. In a HP supercell storm, the initial location of the mesocyclone, which is the parent rotation of tornadoes, is embedded well within the precipitation of the storm, instead of being on the edge of the storm (as in classic and low-precipitation supercell storms). Two 5-cm wavelength mobile Doppler radars were positioned near the storm and collected volume scans every 3 minutes for 3 h beginning as the storm became supercellular. The storm had supercell characteristics for this entire period. The Oklahoma Lightning Mapping Array provided three-dimensional data throughout the storm’s supercellular stage and provided two-dimensional data from the time of storm initiation in western Oklahoma. A 10-cm wavelength polarimetric radar also provided data for much of this period.
Lightning flash rates became extraordinarily large as the storm evolved into a supercell and its motion turned rightward. Flash rates increased again (to an estimated peak value of almost 500 flashes per minute) shortly before the storm produced a tornado rated F2 on the Fujita scale. During this period, an upward pulse in lightning density extended as high as 18 km MSL in a plume extending above the equilibrium level, and the region of lightning activity pulsed eastward far into the anvil, up to 150 km from the western edge of the storm. A series of minimums in the plan projection of lightning density (i.e., lightning holes) formed just above the bounded weak echo region. A dual-Doppler synthesis of wind during one volume scan shows the lightning hole was co-located with large vertical wind speeds in the rotating updraft. The hole apparently occurred because precipitation particles had little time to grow and gain charge in the strong updraft before they were lifted to upper regions of the storm and advected outward by flow from the diverging updraft. Cloud-to-ground lightning activity in and near heavy precipitation was dominated initially by negative ground flashes, but during part of the supercell phase, evolved to become dominated by positive ground flashes. Lightning mapping data suggest that, when positive ground flashes dominated, the vertical polarity of the storm’s electrical structure was inverted from the usual polarity.

MacGorman, D., K. Kuhlman, E. Bruning, D. Rust, P. Krehbiel, M. Biggerstaff, 2007: Small, continual lightning activity in the overshooting turret of supercell storms. Preprints, 2007 Annual Fall Meeting, San Francisco, CA, USA, American Geophysical Union, AE41A-03.

Mansell, E. R., C. L. Ziegler, D. R. MacGorman, 2007: A Lightning Data Assimilation Technique for Mesoscale Forecast Models. Monthly Weather Review, 135, 1732-1748.

Lightning observations have been assimilated into a mesoscale model for improvement of forecast initial conditions. Data are used from the National Lightning Detection Network (cloud-to-ground lightning detection) and a Lightning Mapping Array (total lightning detection) that was installed in western Kansas–eastern Colorado. The assimilation method uses lightning as a proxy for the presence or absence of deep convection. During assimilation, lightning data are used to control the Kain–Fritsch (KF) convection parameterization scheme. The KF scheme can be forced to try to produce convection where lightning indicated storms, and, conversely, can optionally be prevented from producing spurious convection where no lightning was observed. Up to 1 g/kg of water vapor may be added to the boundary layer when the KF convection is too weak. The method does not employ any lightning–rainfall relationships, but rather allows the KF scheme to generate heating and cooling rates from its modeled convection. The method could therefore easily be used for real-time assimilation of any source of lightning observations. For the case study, the lightning assimilation was successful in generating cold pools that were present in the surface observations at initialization of the forecast. The resulting forecast showed considerably more skill than the control forecast, especially in the first few hours as convection was triggered by the propagation of the cold pool boundary.

Mansell, E., C. L. Ziegler, E. Bruning, 2007: Simulated electrification of a TELEX multicell storm. Preprints, 13th International Conference on Atmospheric Electricity, Beijing, China, International Commission on Atmospheric Electricity, 290-293.

Wood, V. T., 2007: OK-WARN: Oklahoma Weather Alert Remote Notification. Preprints, 16th Symposium on Education, San Antonio, TX, USA, Amer. Meteor. Soc., CD-ROM P1.25.

Oklahoma Weather Alert Remote Notification (OK-WARN) is a new service that provides timely notification of weather hazards and emergencies to people with hearing loss via pager, e-mail or cell phone. This program was developed as a partnership between Oklahoma Department of Emergency Management, NOAA National Weather Service, NOAA National Severe Storms Laboratory, Oklahoma Department of Rehabilitation Services, Communication Services for the Deaf of Oklahoma, and Weather Affirmation, LLC. OK-WARN was made possible by a federal grant from the Federal Emergency Management Agency, now a division of the Department of Homeland Security. Since the inception of OK-WARN in 2001, the program has been expanded statewide to serve the deaf and hard-of-hearing community. Information about how OK-WARN operates will be presented.

Wood, V. T., 2007: Impact of Severe Weather on People with Hearing Loss. Weather and Society Watch Vol. 1, No. 4, July 20, 2007, 3 pp.

Wood, V. T., 2007: Improvement of WSR-88D VAD Winds: Cyclonic Wind Fields. Final Report, FY2007 Memorandum of Understanding Between WSR-88D Radar Operations Center and National Severe Storms Laboratory Task 5, 41 pp.

Brown, R. A., T. A. Niziol, N. R. Donaldson, P. I. Joe, V. T. Wood, 2006: WSR-88D monitoring of shallow lake-effect snowstorms over and around Lake Ontario: Simulations of improvements using lower elevation angles. Preprints, 22nd Conference on Interactive Information Processing Systems, Atlanta, GA, USA, American Meteorological Society, CD-ROM, P2.7. [Available from Rodger A. Brown, National Severe Storms Laboratory, 120 David L. Boren Blvd., Norman, OK, USA, 73072.]

Winner, best poster presentation of conference.

Currently, National Weather Service (NWS) WSR-88D radars do not operate below +0.5 deg. Consequently, shallow lake-effect snowstorms over and around Lake Ontario pose a detection (and warning) challenge for the Buffalo, NY, NWS Forecast Office. Limited measurements in the lower portions of the storms preclude reliable quantitative precipitation estimation (QPE) in much of the coverage area.

This presentation will show how we use simulated scanning strategies to investigate how much detections and QPE would improve using lower elevation angles for the three closest New York State WSR-88Ds: Montague (KTYX), Buffalo (KBUF), and Binghamton (KBGM). Canadian radars at King City and Franktown on the north side of the lake—that operate as low as –0.1 and 0.0 deg, respectively—also are considered.

The Montague radar is located east of Lake Ontario on top of the Tug Hill Plateau 520 m above the lake. Using current scanning strategies, 2-km-deep snowstorms are detectable to a range of only 100 km from the radar (covering the eastern quarter of the lake). The Buffalo radar covers the western half of the lake. Being farther from the lake, the Binghamton radar covers snowstorms that extend southeastward from Lake Ontario.

Simulations show that, when the lowest elevation angle for KTYX is decreased to –0.4 deg, the range of detection of 2-km-deep snowstorms increases from 100 to 220 km. Lowering the lowest elevation angle for KBUF and KBGM to +0.2 deg increases the coverage area (2 km above the surface) by about 60%. Lowering the scanning strategies for these three radars and operating in conjunction with the Canadian radars, shallow lake-effect storms would be detected over the entire lake and surrounding coastal regions and reliable QPE information would be available over nearly the entire region.

Brown, R. A., V. T. Wood, D. C. Dowell, 2006: Interpretation of simulated WSR-88D Doppler velocity signatures of tornadoes associated with nonuniform reflectivities. Preprints, 23rd Conference on Severe Local Storms, St. Louis, MO, USA, Amer. Meteor. Soc., CD-ROM, P9.10.

Typically, when simulated Doppler velocity measurements are made across a tornado, one assumes that the associated reflectivity field is uniform. However, recent measurements made by mobile Doppler radars in the immediate vicinity of tornadoes reveal the presence of a low-reflectivity eye centered on the tornado. The eye arises from the centrifuging of debris and hydrometeors within the tornadic circulation.

Dowell et al. (2005) employed an axisymmetric numerical model to study particle motions and concentrations in tornadoes. We used 1.5-mm-diameter raindrops in the model to produce flow and reflectivity patterns for three different sized tornadoes: medium, large, and very large. The model output then was scanned with a WSR-88D emulator to produce simulated reflectivity and Doppler velocity measurements within the tornadoes.

We found that, except for the rare very large tornado, peak Doppler velocity values associated with a low-reflectivity eye at close range occurred at a smaller radius than in the model tornado. These peak Doppler velocity values also were at a smaller radius than peak values associated with a uniform reflectivity pattern. As distance from the radar increased, the widening radar beam smeared the low-reflectivity eye to produce a more uniform distribution of reflectivity. At the same time, the peak Doppler velocity values approached those obtained for a uniform reflectivity distribution. Thus, in a typical tornado near a WSR-88D, we would expect the presence of a low-reflectivity eye to cause the peak Doppler velocity values to appear at a smaller radius than the radius of the true peak tangential velocities.

Brown, R. A., R. M. Steadham, 2006: Site-specific scanning strategies for WSR-88Ds: Planning for field tests.. Preprints, Annual Meeting, Cleveland, OH, USA, National Weather Association, 46-47.

The lowest elevation angle scanned by all radars in the Weather Surveillance Radar–1988 Doppler (WSR-88D) network is 0.5 deg. Users of Terminal Doppler Weather Radars (TDWRs) and research Doppler radars find that scanning at 0.0 deg reveals the presence of boundaries of forecasting significance that frequently are not evident at 0.5 deg elevation angles. Furthermore, forecasters who prepare warnings based on mountaintop WSR-88D measurements frequently find that the radar overshoots hazardous weather phenomena that threaten the surrounding populace. Simulations indicate that the use of negative elevation angles at mountaintop sites would permit the detection of hazardous weather and would greatly improve the accuracy of surface rainfall and snowfall estimates.
With a basic need for WSR-88Ds to scan at lower elevation angles, the WSR-88D Radar Operations Center—in collaboration with National Weather Service Forecast Offices, National Severe Storms Laboratory, and Federal Aviation Administration—is proposing that each WSR-88D collect data at elevation angles that are best suited for its locale. To test the operational feasibility of lowering elevation angles, a two-year field test is being proposed for six WSR-88Ds, three located on mountaintops and three located on relatively flat terrain. The test plan currently is being evaluated at various administrative levels within the National Weather Service.

Burgess, D. W., R. H. Johns, C. A. Doswell, J. A. Hart, M. S. Gilmore, S. F. Piltz, 2006: The Tri-State Torndao of 18 March 1925, Part I: Re-examination of the Damage Path. Extended Abstracts, 23rd Conference on Severe Local Storms, St. Louis, MO, USA, American Meteorological Society, 18.1.

Burgess, D. W., M. A. Fresch, 2006: The ROC/NSSL Technology Transfer MOU: A Success Story in Radar Applications Technology Transfer. Extended Abstracts, 22nd Internation Conference on Interactive Information Processing Systems (IIPS), Atlanta, GA, USA, American Meteorological Society, 9.2.

Elmore, K. L., M. E. Baldwin, D. M. Schultz, 2006: Field Significance Revisited: Spatial Bias Errors in Forecasts as Applied to the Eta Model. Monthly Weather Review, 134, 519-531.

The spatial structure of bias errors in numerical model output is valuable to both model developers and operational forecasters, especially if the field containing the structure itself has statistical significance in the face of naturally occurring spatial correlation. A semi-parametric
Monte Carlo method, along with a moving blocks bootstrap method is used to determine the field significance of spatial bias errors within spatially correlated error fields. This process can be completely automated, making it an attractive addition to the verification tools already in use. The process demonstrated here results in statistically significant spatial bias error fields at any arbitrary
significance level.

To demonstrate the technique, 0000 and 1200 UTC runs of the operational Eta model and the operational Eta model using the Kain–Fritsch convective parameterization scheme are examined. The resulting fields for forecast errors for geopotential heights and winds at 850, 700, 500, and 250 hPa over a period of 14 months (26 January 2001 through 31 March 2002) are examined and compared using the verifying initial analysis. Specific examples are shown, and some plausible causes for the resulting significant bias errors are proposed.

Elmore, K. L., D. M. Schultz, M. E. Baldwin, 2006: The Behavior of Synoptic-Scale Errors in the Eta Model. Monthly Weather Review, 134, 3355-3366.

A previous study of the mean spatial bias errors associated with operational forecast models motivated an examination of the mechanisms responsible for these biases. One hypothesis for the cause of these errors is that mobile synoptic-scale phenomena are partially responsible. This paper explores this hypothesis using 24-h forecasts from the operational Eta model and an experimental version called the EtaKF.
For a sample of 44 well-defined upper-level short-wave troughs arriving on the west coast of the United States, 70% were underforecast (as measured by the 500-hPa geopotential height), a likely result of being undersampled by the observational network. For a different sample of 45 troughs that could be tracked easily across the country, consecutive model runs showed that the height errors associated with 44% of the troughs generally decreased in time, 11% increased in time, 18% had relatively steady errors, 2% were uninitialized entering the west coast, and 24% exhibited some other kind of behavior. Thus, landfalling short-wave troughs were typically underforecast (positive errors, heights too high), but these errors tended to decrease as they moved across the United States, likely a result of being better initialized as the troughs became influenced by more upper-air data. Nevertheless, some errors in short-wave troughs were not corrected as they fell under the influence of supposedly increased data amount and quality. These results indirectly show the effect that the amount and quality of observational data has on the synoptic-scale errors in the models. On the other hand, long-wave ridges tended to be underforecast (negative errors, heights too low) over a much larger horizontal extent.
These results are confirmed in a more systematic manner over the entire dataset by segregating the model output at each grid point by the sign of the 500-hPa relative vorticity. Although errors at grid points with positive relative vorticity are small but positive in the western United States, the errors become large and negative farther east. Errors at grid points with negative relative vorticity, on the other hand, are generally negative across the United States. A large negative bias observed in the Eta and EtaKF over the southeast United States is believed to be due to an error in the longwave radiation scheme interacting with water vapor and clouds. This study shows that model errors may be related to the synoptic-scale flow, and even large scale features such as long-wave troughs can be associated with significant large-scale height errors.

Available online at ://http://ams.allenpress.com/.

MacGorman, D., I. Apostolakopoulos, A. Nierow, J. Cramer, N. Demetriades, P. Krehbiel, 2006: Improved Timeliness of Thunderstorm Detection from Mapping a Larger Fraction of Lightning Flashes. Preprints, 1st International Lightning Meteorology Conference, Tucson, AZ, USA, Vaisala, CD-ROM, N/A. [Available from Vaisala, Inc., Tucson Operations, 2705 E. Medina Rd., Tucson, AZ, USA, 85706.]

One application of lightning ground strike mapping systems has been thunderstorm detection. However, the climatological ratio of in-cloud flashes to cloud-to-ground flashes typically is greater than 2:1. Thus, systems that map either cloud flashes or all types of flashes will detect storms more quickly and reliably. The improvement typically is even greater than would be expected simply from the greater number of samples, because the first flashes produced by a storm usually are cloud flashes. However, the improvement obviously is affected by the fraction of flashes that a lightning mapping system detects. Because it costs substantially more to detect a larger fraction of all flashes, one would like to know how much lead time will be added by various levels of lightning detection. The U.S. National Lightning Detection Network (NLDN) being used by the National Weather Service is now capable of detecting roughly 10-20% of cloud flashes, in addition to a much larger fraction of cloud-to-ground flashes, over the contiguous United States. So far, this cloud flash option has been turned on only in a test region. The optical lightning mapper being planned for GOES-R is expected to detect 80-90% of cloud flashes. Some research mapping systems can detect essentially all but the smallest flashes throughout their coverage region. We analyzed the test cloud flash data from the NLDN network to see how much that system’s cloud flash detection would improve thunderstorm detection. Furthermore, we analyzed data from VHF lightning mapping systems that detect almost all flashes, to evaluate how much the timeliness of thunderstorm detection can be improved over what is now achieved with ground strike mapping systems. In north Texas and Oklahoma, 50% of thunderstorms produced a cloud-to-ground flash within 5-10 minutes of their first cloud flash, but in roughly 10% of storms, no cloud-to-ground flash occurred within an hour of the first cloud flash. Behavior was much different in storms over the High Plains of northwest Kansas and northeast Colorado. There it required 30 minutes after the first cloud flash for 50% of storms to produce a cloud-to-ground flash, and 20% of storms produced no cloud-to-ground flash within their first hour of lightning activity. One might expect such a result on the basis of climatological studies showing that cloud flashes comprise at least 90% of all lightning over much of the High Plains and in a few other regions of the country.

MacGorman, D. R., I. Apostolakopoulos, A. Nierow, J. Cramer, N. Demetriades, P. Krehbiel, 2006: Improved timeliness of thunderstorm detection from mapping a larger fraction of lightning flashes. Preprints, International Lightning Meteorology Conference, Tucson, AZ, USA, Vaisala, 7.

MacGorman, D., K. Kuhlman, M. Biggerstaff, D. Rust, P. Krehbiel, 2006: Lightning and radar observations of the 29 May 2004 tornadic HP supercell during TELEX. Preprints, Annual Fall Meeting, San Francisco, CA, USA, American Geophysical Union, AE343A-1056.

Mansell, E. R., C. L. Ziegler, D. R. MacGorman, 2006: A Lightning Data Assimilation Technique for Mesoscale Forecast Models. Preprints, Second Conference on Meteorological Applications of Lightning Data, Atlanta, GA, USA, American Meteorological Society, 4.2.

Lightning observations have been assimilated into the COAMPS mesoscale model for improvement of forecast initial conditions. Data are used from the National Lightning Detection Network (NLDN, cloud-to-ground lightning detection) and a Lightning Mapping Array (LMA; total lightning detection) that was installed in western Kansas/eastern Colorado. The assimilation method uses lightning as a proxy for the presence or absence of deep convection. During assimilation, lightning data are used to control the Kain-Fritsch (KF) convection parameterization scheme (CPS). The KF scheme can be forced to try to produce convection where lightning indicated storms, and, conversely, can optionally be prevented from producing spurious convection where no lightning was observed. Up to 1 g/kg of water vapor may be added to the boundary layer when the KF convection is too weak. The method does not make any use lightning-rainfall relationships, rather allowing the KF scheme to generate heating and cooling rates from its modeled convection. The method could therefore be used easily for real-time assimilation of any source of lightning observations.

Results will be presented for a warm-season test case 20-21 July 2000, when storms initiated and developed in large systems in Kansas both days. The second round of convection began by 22:00 UTC (20 July), and storm system with strong outflow had developed by 00 UTC on 21 July. Lightning data were assimilated over a 24 hour period (starting at 00 UTC on 20 July), covering the first round of convection and the start of the second. A control run was spun up over the same period only with the usual 12-hourly update cycle. As expected, during the assimilation period the model produces substantially more accurate precipitation (rates and location) than the control forecast. Even when water vapor was added to enhance convection, the rainfall rates were generally less than those indicated by rain gauge data. A forecast was started from the resulting initial condition at 00 UTC on 21 July 2000.

The lightning assimilation was successful in generating the cold pool that was present in the surface observations at initialization of the forecast. The resulting forecast showed considerably more skill than the control forecast, especially in the first few hours as convection was triggered by the propagation of the cold pool boundary.

Available online at ://http://ams.confex.com/ams/Annual2006/techprogram/paper_104180.htm.

Rabin, R. M., T. J. Schmit, 2006: Estimating soil wetness from the GOES sounder. Journal of Atmospheric and Oceanic Technology, 23, 991-1003.

Rabin, R. M., T. Whittaker, 2006: Tool for Storm Analysis Using Multiple Data Sets. Advances in Visual Computing, G. Bebis, R. Boyle, D. Koracin, B. Parvin, Ed(s)., Springer, 571-578.

Wood, V. T., L. W. White, C. R. Alexander, R. L. Tanamachi, 2006: An analytical model of one- and two-celled vortices: Preliminary testing. Preprints, 23rd Conference on Severe Local Storms, St. Louis, MO, USA, American Meteorological Society, CD-ROM, P10.1.

Brown, R. A., V. T. Wood, 2005: Interpretation of Doppler velocity patterns. Doppler Radar Theory and Meteorology, Part B, Doppler Radar Meteorological Observations, Federal Meteorological Handbook No. 11 (Revised), NOAA, 6-1-6-20.

Brown, R. A., 2005: Thunderstorms. The Encyclopedia of World Climatology, Springer, 719-724.

Brown, R. A., K. Tarp, 2005: The National Severe Storms Laboratory: 40 Years Young and Going Strong. Preprints, 21st International Conference on Interactive Information and Processing Systems (IIPS) for Meteorology, Oceanography, and Hydrology, San Diego, CA, USA, American Meteorological Society, CD-ROM, XXXX.

In 1964, the U.S. Weather Bureau's National Severe Storms Project (NSSP) moved from Kansas City to Norman and changed its name to the National Severe Storms Laboratory (NSSL). For the next 25 years, NSSL continued NSSP's (and its predecessors') long-standing tradition of improving understanding of severe storms by conducting a data collection program each spring that included surface and upper air mesonetworks, research aircraft, and radars. Over the years, Doppler radars (including dual polarization), an instrumented TV transmitter tower, storm intercept teams, and storm electricity measurements were added. In more recent years, spring programs have become more intermittent because of funding constraints, with many associated with national research programs (involving airborne Doppler radars) in the southern Plains. Since the early 1990s, various NSSL sensors have become mobile with the addition of mobile rawinsonde release vehicles, balloon-borne storm electricity sensors, mesonetwork instruments on the tops of cars, and Doppler radars mounted on trucks.

Early NSSL research has had a positive impact on improved public safety. Aircraft studies of turbulence in severe thunderstorms, called Project Rough Rider, during the 1960s, 1970s, and early 1980s led to improved commercial airline safety guidelines in the vicinity of thunderstorms. NSSL Doppler radar studies of thunderstorm mesocyclones and tornadoes during the 1970s led to the decision by the National Weather Service (NWS), U.S. Air Force's Air Weather Service, and Federal Aviation Administration (FAA) to include Doppler capability in their updated operational WSR-88D and Terminal Doppler Weather Radar networks. The WSR-88D has helped forecasters significantly improve severe thunderstorm and tornado warnings, saving countless lives. NSSL continues to support the NWS and FAA by developing and refining radar algorithms for identifying severe weather phenomena and estimating precipitation accumulations, and by helping to design better radar acquisition and processing equipment. A program is currently underway to collect data much faster using a newly-constructed phased array Doppler radar.

By the mid 1980s, NSSL was developing an expertise in numerical modeling. Various techniques, including ensembles, are being investigated to improve the numerical prediction of storm-scale, mesoscale, and synoptic-scale processes. In 1997, soon after the National Severe Storms Forecast Center in Kansas City changed its name to the Storm Prediction Center (SPC), it moved to Norman. With the SPC being collocated with NSSL, there have been many opportunities for NSSL meteorologists to help SPC forecasters develop improved severe storm forecasting techniques, including the application of probabilistic forecasting techniques. Thus, through its various research activities during the past 40 years, NSSL has been instrumental in advancing the state of the art of severe storm detection and prediction.

Brown, R. A., B. A. Flickinger, E. Forren, D. M. Schultz, D. Sirmans, P. L. Spencer, V. T. Wood, C. L. Ziegler, 2005: Improved detection of severe storms using experimental fine-resolution WSR-88D measurements. Weather and Forecasting, 20, 3-14.

NSSL Outstanding Scientific Paper Award

Doppler velocity and reflectivity measurements from WSR-88D (Weather Surveillance Radar - 1988 Doppler) radars provide important input to forecasters as they prepare to issue short-term severe storm and tornado warnings. Current-resolution data collected by the radars have an azimuthal spacing of 1.0° and range spacing of 1.0 km for reflectivity and 0.25 km for Doppler velocity and spectrum width. To test the feasibility of improving data resolution, National Severe Storms Laboratory's test-bed WSR-88D (KOUN) collected data in severe thunderstorms using 0.5° azimuthal spacing and 0.25 km range spacing,resulting in eight times the resolution for reflectivity and twice the resolution for Doppler velocity and spectrum width. Displays of current-resolution WSR-88D Doppler velocity and reflectivity signatures in severe storms were compared with displays showing finer-resolution signatures. At all ranges, fine-resolution data provided better depiction of severe storm characteristics. Eighty-five percent of mean rotational velocities derived from fine-resolution mesocyclone signatures were stronger than velocities derived from current-resolution signatures. Likewise, about 85% of Doppler velocity differences across tornado and tornadic vortex signatures were stronger than values derived from current-resolution data. In addition, low-altitude boundaries were more readily detected using fine-resolution reflectivity data. At ranges greater than 100 km, fine-resolution reflectivity displays revealed severe storm signatures, such as bounded weak echo regions and hook echoes, which were not readily apparent on current-resolution displays. Thus, the primary advantage of fine-resolution measurements over current-resolution measurements is the ability to detect stronger reflectivity and Doppler velocity signatures at greater ranges from a WSR-88D.

Brown, R. A., R. M. Steadham, B. A. Flickinger, R. R. Lee, D. Sirmans, V. T. Wood, 2005: New WSR-88D volume coverage pattern 12: Results of field tests. Weather and Forecasting, 20, 385-393.

For the first time since the installation of the national network of WSR-88D radars, a new scanning strategy -- Volume Coverage Pattern 12 -- has been added to the suite of scanning strategies. VCP 12 is a faster version of VCP 11 and has denser vertical sampling at lower elevation angles. This note discusses results of field tests in Oklahoma and Mississippi during 2001 - 2003 that led to the decision to implement VCP 12. Output from meteorological algorithms for a test-bed radar using an experimental VCP were compared with output for a nearby operational WSR-88D using VCP 11 or 21. These comparisons were made for severe storms that were at comparable distances from both radars. Findings indicate that denser vertical sampling at lower elevation angles leads to earlier and longer algorithm identifications of storm cells and mesocyclones, especially those more distant from a radar.

Brown, R. A., J. M. Lewis, 2005: Path to NEXRAD: Doppler radar development at the National Severe Storms Laboratory. Bulletin of the American Meteorological Society, 86, 1459-1470.

In this historical paper, we trace the scientific- and engineering-based steps at the National Severe Storms Laboratory (NSSL) and in the larger weather radar community that led to the development of NSSL's first 10-cm wavelength pulsed Doppler radar. This radar was the prototype for the current NEXRAD (NEXt generation weather RADar) or WSR-88D (Weather Surveillance Radar-1988 Doppler) Network.

We track events, both political and scientific, that led to the establishment of NSSL in 1964. The vision of NSSL's first director, Edwin Kessler, is reconstructed through access to historical documents and oral history. This vision included the development of Doppler radar where research was to be meshed with the operational needs of the U.S. Weather Bureau and its successor the National Weather Service.

Realization of the vision came through steps that were often fitful, where complications arose due to personnel concerns, and where there were always financial concerns. The historical research indicates that: (1) the engineering prowess and mentorship of Roger Lhermitte was at the heart of Doppler radar development at NSSL; (2) key decisions by Kessler in the wake of Lhermitte's sudden departure in 1967 proved crucial to the ultimate success of the project; (3) research results indicated that Doppler velocity signatures of mesocyclones are a precursor of damaging thunderstorms and tornadoes; and (4) results from field testing of the Doppler-derived products during the 1977-1979 Joint Doppler Operational Project -- especially the noticeable increase in the verification of tornado warnings and an associated marked decrease in false alarms -- led to the government decision to establish the NEXRAD network.

Brown, R. A., K. L. Torgerson, 2005: Interpretation of single-Doppler radar signatures in a V-shaped hailstorm: Part II – Evolution of updraft interactions with ambient midaltitude flow. National Weather Digest, 29, 65-80.

Part II of this two-part descriptive study documents characteristics and evolution of the midaltitude flow field arising from interactions of ambient flow with the updraft region of a North Dakota multicell hailstorm. While only single-Doppler radar measurements were available, there were sufficient details in reflectivity and Doppler velocity features to provide interesting deductions about the interactions. The updraft region, located at the upstream end of the storm, typically consisted of two or three actively growing updrafts. Maximum wind speeds occurred along the lateral flanks of the updraft region. The center of the resulting wake region was characterized by a midaltitude channel of low-speed air extending downstream from the middle of the updraft region. Characteristics of the resultant midaltitude vorticity couplet straddling the updraft region did not appear to support the theoretical concept that couplets arise from vertical tilting of low-altitude horizontal vortex tubes. Rather, the vertical momentum of individual updrafts appeared to have collectively presented enough resistance to the approaching midaltitude environmental flow that air slowed down as it flowed through the porous updraft region. As air farther upstream approached the wall of slower-moving air, some of the air was diverted, increasing speed as it flowed around the sides of the updraft region.

Brown, R. A., T. A. Niziol, V. T. Wood, 2005: Improved WSR-88D detection of shallow lake-effect snowstorms over Lake Ontario: Simulations of lowered elevation angles. Preprints, Annual Meeting, St. Louis, MO, USA, National Weather Association, 22-23.

Currently, National Weather Service WSR-88D radars do not operate below +0.5 deg. Consequently, shallow lake-effect snowstorms over and around Lake Ontario pose a detection and warning problem for the Buffalo NWS Forecast Office. We use simulated scanning strategies to investigate how much detections would increase using lower elevation angles for the three closest New York State WSR-88Ds: Montague (KTYX), Buffalo (KBUF), and Binghamton (KBGM). Two Canadian radars on the north side of the lake—that operate as low as 0.0 deg—also are considered.

The Montague radar is located east of Lake Ontario on top of the Tug Hill Plateau 520 m above the lake. Using the current scanning strategies, 2-km-deep snowstorms are detectable to a range of only 100 km from the radar (covering the eastern quarter of the lake). The Buffalo radar covers the western half of the lake. Being farther from the lake, the Binghamton radar covers snowstorms over the southern lake shore.

Simulations show that, when the lowest elevation angle for KTYX is decreased to –0.3 deg, the range of detection of shallow snowstorms increases by 100 km. Lowering the lowest elevation angle for KBUF and KBGM to +0.3 deg increases the coverage range by 20 km. By lowering the scanning strategies for these three radars and operating in conjunction with the Canadian radars, lake-effect storms would be detected over the entire lake and surrounding coastal regions.

Brown, R., V. Wood, 2005: Evaluation of the Velocity Dealiasing Algorithm modified for super-resolution WSR-88D data. Task 5.1, FY 2005 Memo. of Understanding between NWS Radar Operations Center and NSSL, Final Report, 13 pp.

Brown, R. A., 2005: Experimental high-resolution WSR-88D measurements in severe storms: Part II – A tornadic supercell storm. Task 5.3, FY 2005 Memo. of Understanding between NWS Radar Operations Center and NSSL, Final Report, 20 pp.

Brown, R. A., V. T. Wood, 2005: Improvement of WSR-88D VAD winds: Part I – Status report. Task 4, FY 2005 Memo. of Understanding between NWS Radar Operations Center and NSSL, Final Report, 39 pp.

Burgess, D. W., D. C. Dowell, L. J. Wicker, A. Witt, 2005: Detailed comparison of observed and modeled tornadogenesis. Preprints, 32nd Conf. on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, 10R.4.

Elmore, K., 2005: Alternatives to the Chi-Square test for evaluating rank histograms from ensemble forecasts. Weather and Forecasting, 20, 789-795.

MacGorman, D. R., W. D. Rust, P. Krehbiel, W. Rison, E. Bruning, K. Wiens, 2005: The electrical structure of two supercell storms during STEPS. Monthly Weather Review, 133, 2583-2607.

Balloon soundings were made through two supercell storms during the Severe Thunderstorm Electrification and Precipitation Study (STEPS) in summer 2000. Instruments measured the vector electric field, temperature, pressure, relative humidity, and balloon location. For the first time, soundings penetrated both the strong updraft and the rainy downdraft region of the same supercell storm. In both storms, the strong updraft had fewer vertically separated charge regions than found near the rainy downdraft, and the updraft's lowest charge was elevated higher, its bottom being near the 40-dBZ boundary of the weak-echo vault. The simpler, elevated charge structure is consistent with the noninductive graupel-ice mechanism dominating charge generation in updrafts. In the weak-echo vault, the amount of frozen precipitation and the time for particle interactions are too small for significant charging. Inductive charging mechanisms and lightning may contribute to the additional charge regions found at lower altitudes outside the updraft. Lightning mapping showed that the in-cloud channels of a positive ground flash could be in any one of the three vertically separated positive charge regions found outside the updraft, but were in the middle region, at 6-8 km MSL, for most positive ground flashes. Our data are consistent with the electrical structure of these storms having been inverted in polarity from that of most storms elsewhere. We hypothesize that the observed inverted-polarity cloud flashes and positive ground flashes were caused by inverted-polarity storm structure, possibly due to a larger than usual rime accretion rate for graupel in a strong updraft.

MacGorman, D., D. Rust, T. Schuur, M. Biggerstaff, J. Straka, C. Ziegler, E. Mansell, P. Krehbiel, W. Rison, T. Hamlin, L. Carey, E. Bruning, K. Kuhlman, N. Ramig, C. Payne, 2005: Lightning Relative to Storm Structure and Microphysics in TELEX. Polarimetric radar and electrical structure of a multicell storm. Preprints, 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, 10R.7.

MacGorman, D., 2005: Relationships among electrification, lightning, kinematics, and microphysics: Lessons from the interaction of observations and numerical storm simulations. Extended Abstracts, 2005 Annual Fall Meeting, San Francisco, CA, USA, American Geophysical Union, CD-ROM, AE32A-01.

MacGorman, D., C. L. Ziegler, E. Mansell, W. Beasley, B. Fiedler, 2005: Retrieval and assimilation of storm characteristics from both in-cloud and cloud-to-ground lightning data to improve mesoscale model forecasts. Final report to the Office of Naval Research (ONR Grant # N00014-00-1-0525) 1, 54 pp.

MacGorman, D., C. Ziegler, T. Mansell, J. Straka, P. Krehbiel, B. Rison, T. Hamlin, 2005: Applications of advanced lightning mapping technologies to storm research and weather operations. Preprints, Conference on Meteorological Applications of Lightning Data, San Diego, CA, USA, American Meteorological Society, 2.1.

MacGorman, D. R., W. D. Rust, C. L. Ziegler, T. J. Schuur, E. R. Mansell, M. I. Biggerstaff, J. M. Straka, E. C. Bruning, K. M. Kuhlman, N. R. Ramig, C. D. Payne, N. S. Biermann, P. R. Krehbiel, W. Rison, T. Hamlin, L. D. Carey, 2005: Lightning relative to storm structure, evolution, and microphysics in TELEX. Preprints, 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, 10R.7.

Mansell, E. R., D. R. MacGorman, C. L. Ziegler, J. M. Straka, 2005: Charge structure in a simulated multicell thunderstorm. Journal of Geophysical Research, 110, .

A three-dimensional dynamic cloud model is used to investigate electrification of the full life cycle of an idealized continental multicell storm. Five laboratory-based parameterizations of noninductive graupel-ice charge separation are compared. Inductive (i.e., electric field-dependent) charge separation is tested for rebounding graupel-droplet collisions. Each noninductive graupel-ice parameterization is combined with variations in the effectiveness of inductive charging (off, moderate, and strong) and in the minimum ice crystal concentration (10 or 50/L). Small atmospheric ion processes such as hydrometeor attachment and point discharge at the ground are treated explicitly. Three of the noninductive schemes readily produced a normal polarity charge structure, consisting of a main negative charge region with an upper main positive charge region and a lower positive charge region. Negative polarity cloud-to-ground (CG) flashes occurred when the lower positive charge (LPC) region had sufficient charge density to cause high electric fields. Two of the three also produced one or more +CG flashes. The other two noninductive charging schemes, which are dependent on the graupel rime accretion rate, tended to produce an initially inverted polarity charge structure and +CG flashes. The model results suggest that inductive graupel-droplet charge separation could play a role in the development of lower charge regions. Noninductive charging, on the other hand, was also found to be capable of producing strong lower charge regions in the tests with a minimum ice crystal concentration of 50/L.

Rabin, R. M., 2005: Tool for storm analysis using multiple data sets. Published in "Advances in Visual Computing", Lecture Notes in Computer Science (#3804), Bebis et. al, Editors. Published by Springer. Proc. First International Symposium on Visual Computing., Lake Tahoe, NV, USA, University of Nevada-Reno, Desert Research Institute, Berkeley L, 571-578. [Available from Robert Rabin, 120 David L. Boren, Norman, OK, USA, 73072.]

Available online at ://http://www.springeronline.com.

Wood, V. T., R. A. Brown, D. C. Dowell, 2005: Simulated WSR-88D measurements of low-reflectivity eyes associated with tornadoes. 32nd Conference on Radar Meteorology, Albuquerque, NM, USA, American Meteorological Society, CD-ROM, P15R.6.