Medium Range Forecast Exercise for Tallahassee, Florida: A Prototype for Forecasting Along the Gulf Coast in Fall

 
Discussion

The GFS 120 hour 500 hPa forecast verifying on 28 October 2003 shows a major trough in the long wave pattern with an axis just to the west of the longitude of TLH and with cyclonic flow extending almost to the Yucatan, as indicated by the height contours. This would place TLH well within an unusually cold and dry air mass for late October. Climatological mean max/min temperatures for October 28 are 78/52, while the MOS product predicts 64/38, or 14 degrees below the mean. These are reasonable predictions considering the predicted flow pattern. The MOS predictions for dew points in the mid-30’s are also reasonable for this cold, dry air mass. The MOS predictions of clear skies, very low POP’s, and zero QPF are also consistent with the cold, dry air mass. Further, there appears to be no appreciable PVA over TLH in connection with the major upper air trough. There is one weak vorticity center to the northwest of TLH, but it appears that this center and its associated PVA will pass to the north of TLH. Any upward motion that might be generated with this vorticity center would not likely produce any cloudiness or precipitation, given the expected dryness of the air mass.