Forecasts of persistent valley cold pools in the Bonneville Basin by a mesoscale model

Persistent valley cold pools (PVCPs) are topographically-trapped layers of air that are colder than the overlying air mass and that last longer than 24 h. Previous research shows numerical models have a tendency to underestimate PVCP strength and duration, but these studies have not considered the Weather Research and Forecasting Nonhydrostatic Mesoscale Model (WRF-NMM) which is now being used operationally by the National Weather Service with a resolution capable of resolving some mesoscale basins and valleys. Herein, the 2008/09 winter season forecasts of PVCPs in the Bonneville Basin of Utah by the WRF-NMM are considered. While the model has a nocturnal warm bias, it captures daytime high temperatures reasonably well during cold pools. Dew point forecast errors can be quite large with no preference for dry or moist biases. Stability profiles are generally well handled, but inversions are sometimes eroded a few hours too early. The effects of these errors on a forecatser's ability to anticipate hazardous weather during PVCPs is also discussed.