Relative skill of forecasts of downslope windstorms in the Owens Valley, CA

Abstract:

An investigation into the predictability of topographically forced downslope windstorms events in the Owens Valley, CA is detailed here-in using numerical weather prediction (NWP) re-forecasts and examination of a meso-network of long term surface observations. Analysis of the meteorological station network shows that downslope windstorm events tend to be limited in spatial extent to the lee slope of the North South trending Sierra Nevada mountain range, and rarely extend to the Eastern half of the Owens Valley. Rotor events are shown to be characterized by particularly gusty winds. Model simulations, irrespective of boundary and surface layer parameterizations, are generally are not skillful in predicting the downstream extent of downslope windstorms. Re-forecasts of a large number of discrete windstorm events show that the percentage of correctly forecast events decreases with increasing forecast horizon, and the timing error and magnitude error of event-maximum wind speed increases with increasing forecast horizon. The quantitative error values derived here-in provide guidance regarding uncertainty and expected error of operational forecasts of topographically forced high wind events in the Owens Valley.