Monday, 23 January 2017
4E (Washington State Convention Center )
The Great Plains low-level jet (LLJ) can be a significant contributor to the development of severe convective systems such as through northerly advection of relatively warm and moist Gulf air and the promotion of rising motion in the LLJ exit region. Model depiction of LLJ morphology in its timing, strength, elevation, and regional extent is greatly dependent on the accuracy of the planetary boundary layer (PBL) scheme to represent the dynamic processes of boundary-layer (BL) development. This study analyzes differences that occur in the simulation of LLJs with the Weather Research and Forecasting (WRF) model when different PBL schemes are used for a set of select cases from the Plains Elevated Convection at Night (PECAN) program, a field program conducted over the central Great Plains during summer 2015 to investigate the dynamics of nocturnal storms. The goal of this present study, however, is not just to identify systematic differences in WRF LLJ forecasts when different PBL schemes are used, but also to analyze differences in BL dynamics that have direct impact on LLJ evolution. Such environmental effects include the temperature inversion and moistening or drying of the lower BL as well as BL depth. Validation of the WRF forecasts for this study incorporates both Rapid Refresh (RAP) analyses and PECAN radiosonde and lidar observations. Consideration is also given to the veracity of RAP analyses as compared to PECAN observations for select sites in the Great Plains.
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