Analysis of precipitation forecasts from the NCEP global forecast system

Satellite observations extend precipitation measurements from limited-area land surface analyses to near a global view of precipitation. As a result, we are able to verify quantitative precipitation forecasts (QPF) from global forecasts. In this study, QPF from the NCEP global forecast system (GFS) have been analyzed with different lead times from day 1 to day 7 during the period of October 2005 – September 2006. The PERSIANN 0.25 x 0.25 degree satellite-derived precipitation estimates provided by UC Irvine were selected to verify the 1 x 1 degree global QPF. An alternative satellite data - CMORPH precipitation estimates from NCEP/CPC (0.25 x 0.25 degree) was also used to assess the QPF during the same period. We find that uncertainties in observation data greatly affect forecast skill in the GFS. QPF over major continents and oceans were composited to verify regional precipitation at various thresholds. Forecast skill (ETS, RMSE, and bias) and other verification metrics for QPF were compared for different seasons (winter/summer), regions (land/ocean), and zonal districts (tropical, subtropical, and mid-latitudes). Daily QPF for the year demonstrated widely varying forecast skill over different subregions. Since upstream weather over the Pacific Ocean is extremely important for predicting weather over the CONUS. Selected high-impact events were tracked from the Pacific Ocean to the coastal U.S. to examine the propagation of the weather system and the predictability of precipitation. We discuss application of this study to future research for projects related to THORPEX and the next-generation global models, such as Finite-volume Icosahedral Model (FIM) at NOAA/ESRL/GSD.