Utilizing high-resolution WRF model output to improve NWS forecasts in complex terrain

Besides providing typical public weather forecasts and issuing special watches, warnings, and advisories of hazardous weather, National Weather Service (NWS) Forecast Offices also provide routine aviation and fire weather forecasts and services. In the complex terrain of western and central Wyoming, operational NWS model guidance sometimes does not attain the level of detail necessary to capture specific weather events. Diurnal wind flows generally less than 10 mph in mountain valleys and along lee slopes are particularly troublesome, especially in Jackson, Pinedale, Lander, and Cody, Wyoming. Additionally, sustained high winds that occur near and downstream of mountain gaps, such as Dubois, Wyoming, are usually better forecast by numerical models that better represent the terrain. In addition to aviation interests around airports at the previously mentioned locations, fire weather customers require accurate wind forecasts nearly anywhere in the region to assist in firefighting decision-making and to ensure personnel safety.

The NWS forecast office in Riverton, Wyoming has been running a high-resolution local model since early 2003 to augment NWS operational model guidance. The Weather Research and Forecast (WRF) system has been utilized since early 2006 at 4 km horizontal resolution, which is a distinct improvement in detail compared to the 12 km North American Mesoscale Model and approximate 40 km Global Forecast System. Forecasters at the Riverton NWS forecast office make use of the full 3-D output when examining model soundings, cross-sections, and time-height diagrams. Several case studies will be presented to demonstrate the utility of the high-resolution guidance in complex terrain and the need to investigate even finer resolution model output to better capture specific weather events and requests.