The SPoRT ADAS assisted in an unusually-challenging dewpoint forecast on August 8. A cold front had come through north Alabama the previous day, causing dew point temperatures around the area to fall into the lower 60s (and even upper 50s in a few spots as diurnal mixing took hold). Dewpoint temperatures to the south remained in the mid 70s. There was some moisture recovery behind the front that evening, but the front had stalled out just south of the WFO HUN forecast area and was beginning to retreat northward. Early on the midnight shift, we suspected that the front had actually pushed into the forecast area based on the widely-spaced observations in Tupelo, MS, and Haleyville, AL. The just-in 0600 UTC SPoRT ADAS analysis helped confirm this suspicion, which improved our situational awareness and changed the short-term forecast thinking rather significantly.
Since nearly all of the forecast models kept the Huntsville forecast area unseasonably dry for another 24 to 36 hours, the forecast grids did not reflect this impinging moisture. The 0600 UTC analysis further proved its worth when trying to adjust the near-term grids to fit this new paradigm. The analysis was used first to determine which forecast model fit the current conditions most closely; Huntsville’s GFE configuration includes a display of all available model data for each of the main forecast parameters, so the ADAS helped me select and adjust dewpoint grids from the 13-km RUC for the 0900 and 1200 UTC time periods. The 0600 UTC ADAS dewpoint grid was then copied into the forecast grids and intermediate grids were interpolated, allowing some of the “ground-truth” data to be directly incorporated into the near-term forecast.
As mentioned earlier, the new frontal positioning changed the forecast in other ways, including the addition of enhanced wording for heat index concerns in northwest Alabama, and convincing us that a slight chance of showers would be needed over part of the region. (Indeed, it turned out that moisture continued pushing further north through the morning, and we were too conservative with rain chances!)