It is well known that numerical warm season quantitative precipitation forecasts lack significant skill for numerous reasons. Some are related to the model--it may lack physical processes required to realistically simulate convection or the numerical algorithms and dynamics employed may not be adequate. Others are related to initialization-mesoscale features play an important role in convective initialization and atmospheric observation systems are incapable of properly depicting the three-dimensional stability structure at the mesoscale. The purpose of this study is to determine if a mesoscale model initialized with a diabatic initialization scheme can improve short-term (0 to 12h) warm season numerical quantitative precipitation forecasts in the Southeastern United States.

The Local Analysis and Prediction System (LAPS) developed at the Forecast System Laboratory is used to diabatically initialize the Pennsylvania State University/National center for Atmospheric Research (PSU/NCAR) Mesoscale Model version 5 (MM5). The SPoRT Center runs LAPS operationally on an hourly cycle to produce analyses on a 15 km covering the eastern 2/3 of the United States. The 20 km National Centers for Environmental Prediction (NCEP) Rapid Update Cycle analyses are used for the background fields. The MM5 is configured on a 140x140 12 km grid centered on Huntsville Alabama and was run 4 times daily (16, 18, 20, and 22 UTC) producing forecasts out to 12 hours in length.

At the time this abstract was prepared, results from 22 model runs conducted during July 2003 have been evaluated. Standard quantitative precipitation verification statistics for 6 and 12 h forecasts were computed for the MM5 initialized with (hot start) and without (cold start) LAPS. Preliminary results indicate that initializing MM5 with LAPS analyses improved 6 and 12h QPF threat scores, especially for precipitation thresholds greater than 1.0 inches. However, bias scores for the same thresholds were larger. The results for additional months will be reported at the meeting.