Assimilation of CASA and WSR-88D radar data via 3DVAR to improve short term convective weather forecasting

A network of four small radars assembled by the Center for Collaborative Adaptive Sensing of the Atmosphere (CASA) were installed in spring of 2005 located in central Oklahoma area. These four inexpensive and dynamically adaptive radars together with nearby two WSR-88D radars (KTLX and KFRD) now can provide multi-Doppler radar coverage of atmosphere in this region. The KTLX and KFRD radars provide coverage at the upper levels, and are located respectively to the northeast and southwest of and about an equal distance from the CASA network. In this study, a three-dimensional variational data assimilation system (3DVAR) developed at Center for Analysis and Prediction of Storms (CAPS) is used to assimilate observations from this radar network into a storm scale nonhydrostatic NWP model—the Advanced Regional Prediction System (ARPS). One, or two severe thunderstorm cases will be chosen to test the impact of reflectivity and radial velocity of CASA radars on the analysis of convective storms, and the subsequent forecast will be assessed. Experiments will be performed in which the CASA radar data are used with different strategies, such as different number of radars, different assimilation frequencies of volume scans, different spatial and temporal thinning, etc. Our goal is to estimate the benefit of these small CASA radars to short term convective weather warnings and predictions.