Development of a MOS Thunderstorm System for the ECMWF Model

The Meteorological Development Laboratory (MDL) has recently developed an experimental suite of station-based, Model Output Statistics (MOS) guidance from the European Centre for Medium-Range Weather Forecasts (ECMWF) model. To date, guidance for temperature, dewpoint, wind speed and direction, sky cover, probability of precipitation, and precipitation type has been developed. One element that is important to aviation interests and public safety is thunderstorms. This paper describes the development of a MOS thunderstorm system for the ECMWF model and its performance when compared to climatology and corresponding MOS forecasts from the Global Forecast System (GFS) and North American Mesoscale (NAM) models.

Equations for the probability of a thunderstorm and the conditional probability of a severe thunderstorm for 3-, 6-, 12-, and 24-h periods were developed over the CONUS from six years of ECWMF model output. Cloud-to-ground (CG) lightning data from the National Lightning Detection Network (NLDN) and severe weather reports collected by the Office of Climate Water and Weather Services (OCWWS) were used to define the predictand. Results from a k-fold cross-validation test indicate the new ECMWF thunderstorm guidance is superior to corresponding GFS MOS and NAM MOS forecasts, and in some cases, forecast skill and good reliability are achieved out as far as 240 hours in advance. This guidance will be incorporated into the experimental short-range and extended-range ECMWF MOS text bulletins which are restricted to NOAA/NWS use only, and will also be available to NWS forecasters in gridded format as part of an experimental ECMWF gridded MOS suite.