An evaluation of the National Meteorological Center's experimental boundary layer model

For almost a year, the National Meteorological Center (NMC) experimented with a planetary boundary layer model (PBL) to determine its utility in NMC operations. The PEL model is similar to the operational boundary layer model used by the Air Force Global Weather Central (AFGWC). The PBL model has eight levels, surface to 1600 m, and a horizontal grid mesh of 190.5 km over the contiguous United States. Forecasts were based on 0000 G.m.t. data and were run to 24 hours. The parameters forecast by the PBL model include temperature, winds, relative humidity, freezing levels, precipitation type, and severe weather indices. The results show that the NMC PBL model has potential for providing useful forecasts of ceiling/ visibility combination, rain vs. snow delineation, and areas of severe weather and temperature changes over the eastern twothirds of the United States. The PBL model does not perform well over the mountain region or during the summer months.