The Meteorological Development Laboratory (MDL) has long been active in developing forecast guidance techniques for hazardous weather, including lightning, severe local storms, and heavy precipitation. Our most recent research involves the development of thunderstorm and severe local storm guidance for the 3-6 hour forecast period based on output from the Eta model. This research was done in conjunction with the development of a complete suite of Eta-based thunderstorm forecast products.

MDL is responsible for producing the Model Output Statistics (MOS) guidance. In 2000, MDL implemented a statistical weather forecast system based on output from what was then the Aviation (AVN) and medium-range (MRF) runs of the Global Forecast System (GFS). As part of this system, equations to predict the probability of thunderstorms and severe local storms were derived for the contiguous U.S. by using cloud-to-ground lightning and storm data. The AVN MOS thunderstorm and severe local storm forecasts provide guidance for 6 to 72 hours in advance for 6-, 12-, and 24-h periods, from four runs of the AVN. In addition, thunderstorm guidance was developed and implemented from the 00Z run of the MRF for 12- and 24-h periods out to 192 hours.

For the very short-range projections out to 3 hours in advance, MDL developed and implemented automated analysis and forecast techniques based primarily on remote sensor observations, especially lightning data. These experimental advective statistical (ADSTAT) convective forecasts are valid for the 0-3 h time frame. Until now, however, there has been a lack of automated short-range guidance valid for the 3-6 h time period, which is a critical time period for the aviation community . We have recently begun employing statistical techniques based on the Eta model to derive thunderstorm and severe local storm probability equations for the 3-6 h time frame. In addition to the 3-6 h thunderstorm forecast, a complete set of Eta-based thunderstorm guidance extending to 54 hours in advance will be available in 2002. The basic approach for creating these forecast products is described in this paper. Our initial verification results are presented, and comparisons are made between the AVN-based and the new Eta-based thunderstorm guidance. Examples of the performance of the latest objective forecasts during a severe weather outbreak are also presented. With the implementation of this Eta-based development, there will be a complete set of objective thunderstorm guidance from different numerical models available to forecasters starting from the first 3-h period, all the way to day seven.