Verification of WRF Model Forecasts of Windstorms in Southwestern British Columbia

The Pacific Northwest coast of North America regularly experiences windstorms, occasionally severe, during the fall and winter storm season. These storms can cause widespread damage to property and power infrastructure — the most damaging storms impacting southwestern British Columbia (BC), Canada in recent years have left hundreds of thousands of people without power for days. It is therefore important for these storms to be well-forecast in both time and space in order to allow utility companies to prepare to minimize disruption due to power outages. However, numerical weather prediction (NWP) models tend to struggle at accurately forecasting surface wind speeds in areas of complex, mountainous terrain such as southwest BC. There have been few case studies carried out to detail how NWP models perform in forecasting windstorms in this region. To help fill this knowledge gap, several examples of windstorms that caused extensive damage in coastal southwest B.C. from the 2016-17 storm season were selected for case studies. These storms were modeled using 36 different configurations of the Weather Research and Forecasting (WRF) model. Different combinations of microphysics, cumulus, planetary boundary layer, and land surface schemes were chosen to form each configuration. Verification was then carried out by interpolating these wind forecasts to weather station locations across the study region, using bias and correlation as the verification metrics. In general, WRF has a tendency to underpredict the highest wind speeds as measured at more exposed coastal stations, particularly for lower resolution grids. By evaluating each of the different configurations, we determine the best choices of parameterizations for windstorm forecasting in this region. Future research will aim to make further improvements to these best-performing WRF configurations to improve short-term severe windstorm forecasts.