Experimental MOS Precipitation Type Guidance from 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. Initial efforts focused on a limited set of elements: temperature, dewpoint, wind speed and direction, sky cover, and probability of precipitation. This work is described in a separate paper authored by Rudack et al. titled “A First Look at the Meteorological Development Laboratory's Experimental ECMWF MOS System” to be presented at the conference. The experimental suite of ECMWF MOS has now been enhanced with the addition of probabilistic and best category precipitation type guidance. This paper describes the development of the new precipitation type products and their performance when compared to climatology and corresponding MOS precipitation type forecasts from the Global Forecast System (GFS).

A three-category short-range and four-category extended-range precipitation type product has been developed at stations over the contiguous U.S. (CONUS) and Alaska, for the 0000 and 1200 UTC ECMWF model cycles. For the short-range statistical forecast system (through 84 hours in advance), equations for the conditional probability of freezing, frozen, and liquid precipitation types were developed for projections every 3 hours valid on the hour, while the extended-range product includes a fourth rain/snow mix category and forecasts are valid for 12-hour periods through 192 hours. Best category forecasts for both the short-range and extended-range products are derived by applying a statistically-derived threshold to the probability forecasts. These new products developed from the ECMWF are the same as those available in the current operational GFS MOS short-range and extended-range text bulletins.

A cross-validation was performed for the 0000 UTC cycle to compare the skill of the new ECMWF MOS precipitation type guidance to that of climatology and the operational GFS MOS. The skill of the 0000 UTC ECMWF MOS is superior to the GFS MOS for all projections through 192 hours, and in some cases ECMWF precipitation type forecasts have the same skill as GFS forecasts valid 24 hours earlier.