Mixing Height Forecasts for Colorado

Mixing height forecasts are a critical element of fire weather forecasts, because they are one of the key factors to computing and understanding smoke dispersal. Forecasters at the National Weather Service (NWS) Offices in Colorado provide publicly available hourly forecasts of mixing height and smoke dispersal that are updated at least twice daily, and more often as conditions warrant. Mixing height forecasts are no doubt important in the event of a wild fire, but perhaps more importantly they are needed for planned burns, which are desired on a daily basis much of the year. Mixing height forecasts are critical to local, state, and federal burn managers across Colorado as they make plans for controlled burns because if the forecast is overestimated by 1000s of feet, the smoke from a controlled burn can lead to unhealthy conditions and low visibility in heavily populated areas. If the forecast underestimates mixing height by 1000s of feet, the burn managers may not be allowed to burn despite favorable smoke dispersal conditions, costing time and money. In an effort to better serve the fire weather partners across Colorado, the NWS offices in Boulder and Grand Junction are studying the accuracy of mixing height forecasts using a variety of techniques driven by two different model sources: The North American Model (NAM) at 12 km resolution, and the National Blend of Models (NBM) downscaled to 2.5 km. Verifying these forecasts is inherently challenging given there are 2 raobs across the state: one in Grand Junction and one in Denver. This presentation will discuss the challenges with forecasting and verifying mixing heights in complex terrain and discuss potential ways to improve those forecasts across Colorado and perhaps in other areas with complex terrain.