A case study from the 1999 Collaborative Convective Forecast Product project

The leading cause of delays in air travel across the nation is adverse weather conditions. Long, continuous lines of thunderstorms are particularly disruptive to air travel. In an attempt to minimize delays, the National Weather Service (NWS) and the Federal Aviation Administration (FAA) developed the Collaborative Convective Forecast Product (CCFP) to be used by FAA decision makers in routing air traffic across the nation.

The CCFP involves meteorologists at the NWS Aviation Weather Center (AWC), meteorologists at the NWS Center Weather Service Units (CWSU) located at the Air Route Traffic Control Centers (ARTCC) around the nation, meteorologists from various airlines and freight companies as well as specialists at the FAA Air Traffic Control System Command Center (ATCSCC) in Herndon VA. Through a collaborative process, forecasts of thunderstorms around the nation are produced four times daily for two, four and six hours after issuance time.

This paper examines the CCFP process from the point of view of an AWC meteorologist. On July 9, 1999, a long, continuous line of thunderstorms developed from the eastern Ohio valley to the central Plains. This paper attempts to answer the question of how could one forecast such a disruptive line of thunderstorms in advance, in order to alert the FAA Traffic Decision makers.

This paper will focus on the 20, 22, and 00 UTC forecasts issued at 1900 UTC July 9 1999. Satellite and radar imagery as well as surface observations in the time leading up to forecast issuance are examined. Prognostic fields of wind, temperature, and moisture at the surface and aloft, and forecast of variou stability indices from the 1200 UTC ETA model and the 1500 UTC Rapid Update Cycle (RUC2) model are examined. Observed and prognostic fields which were useful in forecasting this long line of thunderstorms are identified. Finally, conclusions on how to forecast long, continuous lines of thunderstorms are presented.