Boundary Layer, Urban Meteorology and Land-Surface Processes

The Dryline, Convective Initiation, and Rapid Evolution of Drought in Oklahoma During 2011

Paul Flanagan
OU School of Meteorology

06 May 2015, 1:00 PM

National Weather Center, Room 5720
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

During the warm season of 2011, a rapid expansion of drought conditions (i.e., flash drought) occurred across eastern Oklahoma. In a matter of weeks, portions of the state transitioned from a rating by United States Drought Monitor (USDM) of no drought conditions to moderate/severe drought conditions. The goal of this study was to investigate the environmental feedbacks during the period spanning March-August 2011 and determine the role of surface conditions on the evolution of the dryline, convective initiation, and rapid drought development that occurred over the eastern region of Oklahoma. Results show that conditions over western Oklahoma continued to deteriorate during April and May, while eastern Oklahoma received below to normal temperatures and excessive rainfall. During the month of June extreme temperatures and wind anomalies forced a rapid depletion of soil moisture by evapotranspiration and flash drought occurred.
Analysis of the dryline during the period shows that on average dryline longitude was further to the east than the climatological normal. Overall, 17 dryline events were analyzed during the month of May accounting for 55% of the days in the month. Of these events, 13 produced convective clouds, with 7 of these producing precipitation. The dryline events that produced precipitation during May versus those that only produced convective clouds without precipitation were, on average, 1.7° further to the east. Preliminary model analyses, using the Weather Research and Forecasting (WRF) Advance Research (ARW) model were completed to diagnose the sensitivity of the dryline to surface conditions. Soil moisture sensitivity tests were completed on a select dryline case to investigate the role of the heterogeneous soil moisture field on the precipitation patterns produced by select drylines. The results demonstrated that the soil moisture conditions impacted the evolution of the dryline and convective initiation.

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