Precipitation forecasts using the Battlescale Forecast Model

The U.S. Army Research Laboratory has developed a mesoscale model; the Battlescale Forecast Model (BFM), which is a tailored version of the HOTMAC hydrostatic model from Yamada. Designed for boundary-layer applications for the Army, the BFM employs a horizontal resolution of 10 km, with 16 terrain-following vertical levels and a top of 7000 m above the highest elevation of the grid. Typically, a 24-h forecast with a 51*51*16 grid configuration takes less than an hour to run on a single-processor Sun Ultra Sparc. This rapid run-time can be attributed to the single nest and no moist physics or cumulus parameterization routines. Despite this, the BFM does output a non-convective precipitation rate as well as a convective precipitation total derived in the post-processing mode of the model run. Because there are no microphysical processes of the non-convective precipitation formation, the precipitation rate is parameterized as a function of cloud liquid water. Using the scheme developed by Sundquist in 1989, the basic assumption for this statistical cloud model is: the denser the cloud, the higher the precipitation rate. To account for convective precipitation, several statistical and empirical techniques were combined. Starting with a regression equation, thunderstorm probability was derived, and then using convective temperature, precipitable water, and instability at each model grid point, a total forecast of convective precipitation was added to the model-derived stratiform total. Over the past few years, several studies were done to examine the effectivness of these BFM techniques over many different climate regimes in the United States. Examples will be shown of stratiform and convective events with an emphasis on New Mexico storms. Results were compared to other hydrostatic numerical models and these results will be presented in the paper.