11th AMS Conference on Numerical Weather Prediction
Norfolk, Virginia, 19-23 August 1996, in press



Harold E. Brooks1, David J. Stensrud1, M. Steven Tracton2, Eric Rogers2,3

1NOAA/ERL/National Severe Storms Laboratory

Norman, Oklahoma

2NOAA/NWS/National Centers for Environmental Prediction

Camp Springs, Maryland

3General Sciences Corporation

Laurel, Maryland


In the summer of 1994, the National Meteorological Center (NMC), now the National Centers for Environmental Prediction (NCEP), and the National Severe Storms Laboratory (NSSL) hosted a workshop on short-range ensemble forecasting (SREF) (Brooks et al. 1995). One outcome of that workshop was the design of a one-year pilot project designed to test the operational uses of ensemble forecasting on the 0-48 hour time range. The final implementation of the project differs slightly from that described in Brooks et al. (1995). The primary difference is that, in addition to the suite of 10 members from the 80-km horizontal resolution Eta model (Black 1994), 5 members from the regional spectral model (RSM) (Juang and Kanamitsu 1994) are also run. Also, the ensemble ended up being typically scheduled for initialization at 1200 UTC on Tuesdays, rather on a date selected each week. (The schedule was altered due to computer and staff availability at the appropriate times.) Here, we would like to report briefly on the status of the pilot project.


The ensemble has now been run more than 30 times, yielding a data set that spans most of a year (Table 1). Data from the model simulations, as well as corresponding 29-km "meso-Eta" forecasts are available for downloading from NSSL via>, along with software to view the data in x-windows environments. Generally, six-hourly data files of winds, height, tem- perature, etc., at every 50 hPa, as well as forecasts of parameters such as CAPE, Lifted Index, and categorical precipitation type are available.
Case studies of individual forecasts (e.g., Brooks et. al. 1996a,b, Cohen et al. 1996) have been done and indicate that, at least in some cases, the ensemble can offer significant value to forecasters. Statistical analy- ses of the larger data set (Hamill and Colucci 1996a,b, Hamill et al. 1996, Stensrud et al. 1996) show that, although the mean and median ensemble forecasts exhibit less error than corresponding meso-Eta forecasts for many variables, the dispersion of the ensemble is less than ideal. Most likely, this is due to the lack of spread in the initial conditions. Techniques for increa-sing the spread are under investigation by groups using other models or initialization techniques for SREF (e.g., Manikin 1995, Manikin and Ramamurthy 1996, Du et al. 1996, Stensrud et al. 1996b). These efforts typically use larger ensembles, but on fewer cases.
Cohen et al. (1996) have focused on the problem of providing information to forecasters from the ensemble. Because of the number of cases involved, the pilot project provides an ideal ground for testing methodologies across a range of conditions and forecasting problems.
The pilot project has succeeded in its goals of showing potential value of operational SREF and in identifying areas where research efforts need to be focused. First, work needs to be done on the problem of developing initial perturbations that span the range of possibilities realistically. The current technique, using differing analyses prepared by NCEP and some members of the medium-range ensemble breeding modes, does not provide a wide enough range. Secondly, the issue of presenting information to forecasters in a useful way is important. Even a 10 member ensemble provides a tremendous amount of data and, presumably, it is important to present information about some of the outliers in the ensemble to help forecasters in dealing with rare, severe events. The challenge of keeping track of all of the members of an ensemble and identifying important features quickly is formidable and requires much work. We invite others to join us in this effort and to utilize this rich source of information about numerical models.


Drs. Henry Juang and Zoltan Toth (NCEP) did the development to produce the RSE ensemble generation technique. Danny Mitchell (NSSL) developed the xgribview software and archival work. We also thank Drs. Geoff DiMego and Eugenia Kalnay (NCEP) for his support during the project.


Black, T., 1994: The new NMC mesoscale Eta model: Description and forecast examples. Wea. Forecasting, 9, 265-278.
Brooks, H. E., M. S. Tracton, D. J. Stensrud, G. DiMego, and Z. Toth, 1995: Short-range ensemble forecasting: Report from a workshop (25-27 July 1994). Bull. Amer. Meteor. Soc., 76, 1617-1624.
_____, J. V. Cortinas Jr., P. R. Janish, and D. J. Stensrud, 1996a: Application of short-range numerical ensembles to the forecasting of hazardous winter weather. Preprints, 15th Conf. on Weather Analysis and Forecasting, Amer. Meteor. Soc., Norfolk, Virginia, this volume.
_____, D. J. Stensrud, and C. A. Doswell III, 1996b: Application of short-range NWP model ensembles to severe storm forecasting. Preprints, 18th Conf. on Severe Local Storms, Amer. Meteor. Soc., San Francisco, Californiaa, 372-375.
Cohen, A. S., T. M. Hamill, and S. J. Colucci, 1996: Evaluating Eta/RSM ensemble forecasts and display methods during selected heavy precipitation events of 1995-96. Preprints, 15th Conf. on Weather Analysis and Forecasting, Amer. Meteor. Soc., Norfolk, Virginia, this volume.
Hamill, T. M., and S. J. Colucci, 1996a: Verificaiton of Eta/RSM short-range ensemble forecasts. Mon. Wea. Rev., submitted.
_____, and S. J. Colucci, 1996b: Random and systemation error in NMC's short-range Eta ensembles. Preprints, 13th Conf. on Probability and Statistics, Amer. Meteor. Soc., San Francisco, California, 51-56.
_____, S. J. Colucci, and A. S. Cohen, 1996: Eta/RSM ensemble usefulness for short-range forecasts: Dependence on weather regime, model, and perturbation methodology. Preprints, 15th Conf. on Weather Analysis and Forecasting, Amer. Meteor. Soc., Norfolk, Virginia, this volume.
Juang, H.-M., and M. Kanamitsu, 1994: The NMC nested regional spectral model. Mon. Wea. Rev., 122, 3-26.
Manikin, G. S., 1995: Short range ensemble forecasting. M. S. Thesis, Dept. of Atmospheric Sciences, University of Illinois at Urbana-Champaign, 100 pp.
_____, and M. K. Ramamurthy, 1996: Short-range Eta model ensemble forecasting. Preprints, 11th Conf. on Numerical Weather Prediction, Amer. Meteor. Soc., Norfolk, Virginia, this volume.
Du, J., S. L. Mullen, and F. Sanders, 1996: Short-range ensemble forecasting (SREF) of quantitative precipitation. Mon. Wea. Rev., submitted. (Short version in this volume.)
Stensrud, D.J., H. E. Brooks, and D. V. Mitchell, 1996a: Validation of the short-range ensemble forecasts in upper levels. Preprints, 11th Conf. on Numerical Weather Prediction, Amer. Meteor. Soc., Norfolk, Virginia, this volume.
_____, D. J., J. W. Bao, Y. Zheng, and T. T. Warner, 1996b: Ensemble forecasting of convective weather events. Preprints, 11th Conf. on Numerical Weather Prediction, Amer. Meteor. Soc., Norfolk, Virginia, this volume.

5 Jan. 1995NoNoTest case
9 May 1995YesYesSevere weather in eastern US (Brooks et al. 1996b)
20 May 1995YesYesFlooding at end of forecast in North Dakota
30 May 1995YesYesSevere weather in Texas
6 June 1995YesYes
13 June 1995YesYes
20 June 1995YesYesRapidan River, Virginia flash flood
27 June 1995YesYes
3 July 1995YesYes
18 July 1995YesYes
25 July 1995YesYes
1 Aug. 1995YesNoHurricanes Dean and Erin (Cohen et al. 1996)
7 Aug.1995YesNoFlooding in Ohio
14 Aug. 1995YesYes
21 Aug. 1995YesYes
29 Aug. 1995YesYesTropical Storm Jerry in Florida
12 Sep. 1995YesNo
18 Sep. 1995YesNo
25 Sep. 1995YesYesHurricane Ishmael flooding in New Mexico
2 Oct. 1995YesNoHurricane Opal in Gulf of Mexico
23 Oct. 1995YesYesHeavy snow in northern Plains
8 Nov. 1995YesYesLake effect snows
13 Nov. 1995YesNoHeavy snow in Northeast
20 Nov. 1995YesNo
27 Nov. 1995YesNoHeavy snow in several areas
11 Dec. 1995YesYesSnows in Midwest, lake effect snows
18 Dec. 1995YesYesHeavy snow NE US, rain southern US (Cohen et al. 1996)
26 Dec. 1995YesYes
11 Jan. 1996YesNoMid-Atlantic snowstorm
23 Jan. 1996YesYes
31 Jan. 1996YesYesArctic outbreak, major winter storm in South (Brooks et al. 1996a)
7 Feb. 1996YesYesNorthwestern US heavy rains
8 Apr. 1996YesNo

Table 1: List of dates for which short-range ensemble was run , beginning at 1200 UTC, and archived at NSSL as of date of writing of manuscript. Yes or no indicates whether RSM or meso-Eta model data are available in the archive. Selected events or particular interest and relevant references included. Note that lack of availaility of meso Eta data in the NSSL archive does not mean that the meso-Eta was not run on that day.