Real-time, Low-level Wind Analysis including CASA and WSR-88D Radar Data using the ARPS 3DVAR

The high spatial and temporal resolution and much improved low-level data coverage provided by CASA's Oklahoma radar network yields an unprecedented opportunity for producing detailed low-level wind analyses for real-time warning and prediction applications. Such analyses are aided by the availability of dual- or even triple-Doppler wind coverage within parts of the CASA domain, and by 5-min sampling of surface wind measurements from the Oklahoma Mesonet. Towards this goal, the general-purpose Advanced Regional Prediction System (ARPS) three-dimensional variational (3DVAR) analysis package was adopted to produce low-level wind analyses in real-time every 5 minutes at 400-meter horizontal resolution. The 3DVAR has been run in real-time each spring since 2008, with analysis products available to off-duty National Weather Service forecasters for evaluation within the NOAA Hazardous Weather Testbed (HWT) Experimental Warning Program. Specifically, data from four CASA radars, two WSR-88D radars, and Oklahoma Mesonet data were analyzed in real-time. The NCEP NAM model forecasts interpolated to the analysis times were used as the analysis background. The high-resolution CASA radar data, utilizing multi-Doppler coverage, significantly improved the low-level wind analyses, especially in terms of capturing low-level rotation features. The CASA radars scan detailed structures at low-levels, which are often partially or entirely missed by the WSR-88Ds at long distances. The wind analyses were found to be of great value to forecasters in the HWT, and the products directly influenced the issuance of at least one (unofficial) tornado warning. Several examples from the 2009 and 2010 spring experiments will be presented, including data from an EF2 tornado event on May 13th 2009 in Anadarko, Oklahoma.