Improving high-resolution model forecasts of downslope winds in the Las Vegas Valley
Pattantyus, Andre K.
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Numerical simulations for severe downslope winds as well as trapped lee waves in Nevada's Las Vegas Valley were performed in this study. The goal of this study was to improve model forecasts of downslopewind-event intensities. This was measured by assessing different planetary boundary layer (PBL) schemes in themountain-valley region. The Weather Research and Forecasting Model was adopted for this research. The numerical experiments were constructed using two nested domains, with 4- and 1-km grid resolution. The working hypothesis was that the occurrence of low-level wind shear and surface gustiness in the Las Vegas Valley was guided by the inversion layer in the valley. The choice of boundary layer scheme and model vertical resolution will influence inversion-layer height and consequently result in significant differences in surface wind and temperature forecast error below some near-surface height. Simulations of severe downslope wind events on 15 April 2008 and on 4October 2009 were conducted. Statistical analyses of model results fromthree different PBL schemes and different vertical resolutions were performed. The results from the domain with 1-kmgrid spacing demonstrated remarkable detail of the severe downslopewinds associated with low-levelwind shear and surface gustiness in the Las Vegas Valley. The simulation results demonstrated that model vertical resolution was primarily responsible for the detail of the lower-level wind and temperature structures. The inverse Froude number and Froude number are two indices that may be included as the forecasting guidance for downslope winds, lee waves, and rotors for the Las Vegas Valley.