School of Meteorology (Defense)

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

Paul Flanagan

05 August 2015, 10:00 AM

National Weather Center, Room 5930
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

During the 2011 warm season, extreme drought conditions impacted the entire state of Oklahoma, resulting in devastating conditions for wildlife, livestock and crops. To better understand the evolution of this drought, a detailed investigation into the drought evolution was completed. Surface observations from the Oklahoma Mesonet provided unique insight of drought development during the study period (March-August), and specifically a “dry and wet” regime that developed over the state caused by atmospheric patterns. Further, dryline position was analyzed and a set of dryline statistics was created. The results showed the atmospheric pattern impacted surface conditions and by creating and maintaining this “dry and wet” regime further impacted the location of the dryline.
To quantify the impact of variable surface conditions on dryline evolution and convective initiation (CI) during April and May 2011, simulations were completed using the WRF-ARW for multiple dryline cases. Specifically, soil moisture conditions were altered to “wet” and “dry” across the entire domain by replacing the CONTROL soil moisture values by each soil category’s soil porosity (wet) or wilting point (dry) volumetric soil moisture value. As a result, numerous impacts on the dryline boundaries simulated in each simulation were noted when compared to the CONTROL simulation which utilized high resolution land data assimilation system (HRLDAS) surface conditions as truth for the initialization of soil moisture. Overall, the dryline boundary, dryline position, and CI during each case were modified depending on the removal or addition of soil moisture over the domain. Further, the position of the dryline during May, under weak synoptic forcing or quiescent conditions, was extremely sensitive to surface conditions depending on the location of the original dryline boundary in conjunction to the specific modification of soil moisture. This was compared to April dryline simulations in which the differences were not as significant. The simulations demonstrated that modifying surface conditions definitively impacted the nature of the dryline during this period, and showed that soil moisture conditions which developed during the early warm season in 2011 (1) modified the typical dryline pattern and (2) led to the evolution and perpetuation of drought over Oklahoma in 2011.

School of Meteorology (Defense) Seminar Series website