NOAA/National Severe Storms Laboratory

June 30 - July 1, 1998, Boulder, 1998

There are three main sections to this report separated by horizontal lines.

The following excerpts are from the draft of a workshop summary paper by Tammy Weckwerth et al, submitted to BAMS. You may contact the lead author at: NCAR, P.O. Box 3000, Boulder, CO 80307-3000, or electronically at

From the “Abstract”

“A workshop on remote sensing of lower-tropospheric water vapor, jointly sponsored by the National Center for Atmospheric Research (NCAR) and the National Oceanic and Atmospheric Administration (NOAA), was held on 30 June and 1 July 1998 at NCAR in Boulder, CO. The workshop commenced with scientists from various disciplines presenting their needs for improved water vapor measurements. Engineers and scientists representing water vapor measuring platforms and retrieval methods presented information on the current technology and plans for improvements. The workshop concluded with a general recommendation and several specific recommendations.”

From “Workshop recommendations”

“ Participants at the water vapor workshop representing the climate, mesoscale, weather prediction, chemistry and boundary layer communities agree that quantitative measurements of water vapor in time and space are critical for their respective areas of research. While in situ sensors, such as aircraft probes and radiosondes, are essential and will continue to provide an important source of water vapor measurements, the scientists expressed concern that these techniques alone are insufficient. Accordingly, the participants of this workshop strongly support the use, improvement and development of active and passive remote sensing techniques to obtain 4-D fields of water vapor.”

The Importance Of Water Vapor Observations To TIMEx

(Outline, by J. Schneider; please note that this represents the unmet needs of those PIs testing hypotheses on surface-based initiation.)

We (at NSSL) became focused on the problem of convective initiation during VORTEX, experiencing extreme frustration forecasting if/where/when severe storms would initiate.

The problem is of wide interest to many scientists and organizations.

Our approach to program development is modeled after VORTEX: scientists develop hypotheses that can be verified or refuted with observations, and work collaboratively to develop opportunities to test those hypotheses.

I saw an excellent example illustrating our need for both scanning and highly mobile capabilities as I drove to the meeting (Loretta: include image here again from title page showing line of convection). A single line of convection persisted for hours, with several growing into small towering Cu, and only a few growing into small severe storms. The length of the line was on the order of 100 kilometers, but the initial width appeared to be on the order of a kilometer, with roughly similar cell spacing. There was no apparant reason why some of the cells along the line became towers, and why a few of those became storms.

My current thinking about this type of isolated initiation event:

To achieve severe weather, there appears to be a hierarchy of stages of convection, separated by process-state changes, which represent changes in the organization of contributory water vapor (I don’t know which of the latter comes first).


clear-air convection -> small Cu -> narrow towering Cu, quickly dissipating -> vigorous towers -> mature cells -> severe weather

What are the criteria for each of these organizational state changes?

Even casual perusal of data reveals:

- organization is not regular in any direction (note variations along lines of convection);
- rapid evolution, with fast state changes;
- elevated dry or moist layers may play a role (surface probes will miss these).

All of which leads to the:

TIMEx Best Guess Wish List

Project Goal: Test hypotheses concerning convective initiation mechanisms over the continental United States (initial investigations in the treeless portions of the Great Plains).

Focus of remote and in situ observations: Wind and water vapor fields in and just above the convective boundary layer during daylight hours (mostly clear air). Scanning Doppler radars on aircraft and trucks can provide 4-D definition of the wind field on a restricted range of scales. We need comparable 4-D information on the water vapor field. Mobile profiling systems (i.e., without scanning capabilities) would be better than nothing, but would fall short of our real requirements.


- range minimum: a few hundred meters;
- range maximum: 10 - 30 km;
- resolution: 10’s to 100’s m;
- restrictions for applications: need clear-air capability; anything beyond would be “icing on the cake”;
- long-term stability, robustness: must be suitable for operation in rough conditions (aircraft or trucks, the latter with short park-to-scan times);
- suitable platforms: aircraft, vans/trucks;
- power consumption: mobile, off either aircraft systems, or generator;
- developing and operating cost: the cheaper, the more we can use it;
- availability: need to have opportunity for university and NOAA scientists to utilize these systems;
- future potential: improvements in resolution and accuracy are always desirable;
- power and safety: reasonable eye-safety would simplify operations.

Meeting Notes (by J. Schneider)

This was a marvelous meeting, offering a great deal of information on existing and possible observing systems, their advantages, and their limitations. We came away with a much clearer picture of the possibilities relative to TIMEx needs, both in terms of taking advantage of existing systems, and in targeting new or evolving systems. Existing systems included mobile staring (not scanning) microwave radiometers (DRI) and AERI systems (U. of Wisc.), both producing time series of integrated water vapor. These are potentially useful as constraints on scanning systems, as well as possible scouting systems to find significant concentrations of water vapor. Possible systems discussed included airborn, scanning water vapor DIAL, and tomographically derived mesoscale-resolution water vapor profiles from GPS networks (larger scale, pseudo-4D). A mobile scanning water vapor DIAL system was particularly attractive, primarily due to it’s potential as a self-calibrating system. But at this point in time, no group seemed to be interested in pursing the development of such a system. Even once a “champion” is found, it might still require several years for development.