Forecasting mixed-layer height over complex terrain

The National Weather Service produces routine fire weather forecasts, including smoke management forecasts, which are specifically tailored for use by the government land and fire management agencies, as well as, for state and county emergency management organizations. A critical component of the smoke management forecast is the mixed-layer height of the atmosphere. The Grand Junction WFO (GJT) forecasters usually generate a mixing height gridded forecast based on the numerical guidance for the entire GJT county warning area (CWA). They provide validation by using observational techniques to calculate the mixing height from the GJT sounding (elevation ~1500 m MSL). Based on customer feedback from fire managers, mixing height and subsequent smoke management forecasts over the higher terrain tend to be under-forecasted during stagnant atmospheric environments. In these events, an upper level ridge is present and usually accompanied by a subsidence inversion aloft between 700 hPa-500 hPa. To investigate this forecast problem, we propose to take a series of upper air radiosonde observations over the elevated mountain terrain to the south of Grand Junction (elevation ~2500 m MSL) to establish the extent and depth of the mixed layer over the higher terrain. These observations will then be compared to the observed valley mixing heights and NCEP model forecasted mixing heights. To supplement this study, additional comparisons to the fire weather forecasts from the high resolution MM5 forecast model run at the USFS Rocky Mountain Center in Fort Collins, CO will be conducted.