Session 18.5 Convection initiation and storm evolution forecasting using radar refractivity retrievals

Friday, 31 October 2008: 9:00 AM
North & Center Ballroom (Hilton DeSoto)
David Bodine, Atmospheric Radar Research Center, School of Meteorology, University of Oklahoma, Norman, OK; and P. L. Heinselman, B. L. Cheong, R. Palmer, and D. S. Michaud

Presentation PDF (2.2 MB)

Radar refractivity retrievals from the Oklahoma City WSR-88D (KTLX) during the spring of 2007 and 2008 have demonstrated numerous applications in forecasting convective initiation and storm evolution. Radar refractivity provides surface moisture data with high spatial and temporal resolution, and previous studies have shown that high-resolution moisture measurements are critical for convective initiation forecasts. This paper illustrates several forecasting applications of refractivity for three storm cases. On 30 April 2007, refractivity data showed that small-scale changes in moisture could be observed and used to determine where isolated thunderstorms developed. These small-scale changes in moisture eliminated convective inhibition locally and allowed convective initiation within an environment of higher convective inhibition. Moreover, refractivity data could also be used to detect boundaries before convergence lines became well defined in reflectivity. The refractivity data enables forecasters to assess the moisture changes across the boundary, which cannot be done using reflectivity data. For the 1 May 2008 case, refractivity data showed increased moisture convergence caused by the collision of a moist boundary and the dryline, which led to convective initiation. Refractivity also can detect outflow from storms, which allows forecasters to monitor its impact on surrounding storms. The 22 April 2008 case showed a storm collapsing as the outflow from another storm cutoff its inflow of warm, moist air. The outflow was not observed in the reflectivity data and was too far from a Mesonet station to be observed until the storm had collapsed. These cases illustrate the utility of radar refractivity data in convective initiation and storm evolution forecasting. Plans for expanded experiments using several radars will also be discussed.
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