Since the summer of 1995 I've been involved in discussions on a possible convective initiation field study with several scientists including NSSL colleagues Erik Rasmussen and Lou Wicker (formerly affiliated with Texas A & M University), Jeanne Schneider (NSSL and USDA/ARS), and Jerry Straka of the University of Oklahoma School of Meteorology (OU/SOM). These discussions were partially prompted by the difficulties we have faced in deploying instruments to observe severe storms when convection fails to develop in high severe threat areas, most notably in VORTEX. Of much greater and indeed fundamental significance, these problems are routinely faced by operational severe storm forecasters whose Quantitative Precipitation Forecasts (QPFs) are often intimately tied to the development of convective storms and Mesoscale Convective Systems during the warm season.

Our goal is to resolve the interconnected boundary layer and convective cloud evolution sufficiently well to quantify the convective initiation process over focused target regions of small-mesoscale spatio-temporal extent. We view fundamental gains in process understanding as the vital prerequisite to the refinement of conceptual cloud and mesoscale models, setting the stage to ultimately improve convective QPFs produced by mesoscale weather prediction models. We believe our goal is closely related to aspects of the observation of continental convection and optimal mix of mesoscale observations as proposed by the United States Weather Research Program (USWRP). To accomplish our goal we intend to field a water vapor DIAL system, two ground-based radars, and additional mobile sensors.

This convective initiation experiment, dubbed the "Thunderstorm Initiation Mobile Experiment" or TIMEx, would be conducted in multiple phases and would employ an armada of aircraft carrying various in-situ and remote sensors, multiple mobile ground-based scanning remote sensors, mobile profilers, and mobile mesonets. A key to our success will be the deployment of mobile radars and water vapor differential absorption DIAL systems capable of optically clear boundary layer airflow, water vapor, and cloud sensing of the same volumes being sampled by the various mobile in-situ platforms. I envision that TIMEx will focus on the preconvective environment, and would not investigate the morphology or evolution of precipitating weather systems that are subsequently spawned by the initial convection. It is important to concentrate all available mobile sensing systems to adequately examine the evolution of the preconvective boundary layer, avoiding entirely the problem of diluting available observing resources over too wide a range of spatio-temporal scales of deep convection and its mesoscale environment.

As of 15 June 1999, we have held four TIMEx Planning Meetings and have participated in the Water Vapor Workshop held in Boulder, CO. The first TIMEx Planning Meeting was hosted by NSSL-Norman in November 1997, and a smaller follow-on meeting was held in Phoenix, Arizona earlier in January 1998 during the AMS Annual Meeting. We've also held meetings at the Severe Storms Conference in Minneapolis in September 1998, and in Boulder in October 1998.

The International H2O Project (IHOP) Planning Meeting in Boulder in April 1999 included a presentation on TIMEx objectives and how these would be strongly enhanced by access to a new ground-based scanning DIAL sensor being planned by NCAR. We are presently concentrating efforts toward the development and field testing of mobile remote and in-situ sensors to be fielded with at least one airborne DIAL system and an airborne cloud-sensing radar system in support of the convective initiation component of the upcoming IHOP field study. IHOP is being planned for May-June 2002 in the region of the eastern Texas and Oklahoma Panhandles, western Oklahoma, and southern Kansas on the Southern U.S. Plains.