Monday Weather Blog: Midweek Rains Coming

By: Meteorologists Ray Hawthorne and Mike McCall Email
By: Meteorologists Ray Hawthorne and Mike McCall Email

A strong pressure gradient between a high centered in Eastern Canada and lowering pressures in the Southern High Plains will maintain a swift breeze through Tuesday. We expect sustained winds between 15 and 20 mph during the day and 5 to 10 mph at night. Aviators should be prepared for strong wind shear -- winds from 30 to 40 knots -- between 2,000 and 4,000 feet AGL (above ground level) after midnight and before noon. Meanwhile, mariners can expect winds in the 15 to 20 knot range nearshore and closer to 30 knots more than 20 nautical miles out. Lows will slowly drop into the mid and upper 50s with the pleasant by Tuesday morning. Highs will be close to the 80 degree mark again in the afternoon, but temperatures will be slightly lower from Tallahassee westward as the winds veer to a more south-southeasterly direction. These winds advect a cooler airmass from the shelf waters of Apalachee Bay. The Eastern Big Bend, Suwannee Valley and South Georgia will have the warmest temperatures.

The global and regional models are now in much better agreement with respect to the timing of Wednesday's storm system. A deep trough in the Southwestern United States and Northwest Mexico this afternoon is expected to reach the Southeastern United States on Wednesday. Today's GFS and ECMWF have trended slower and now look more like yesterday's experimental NAM, Canadian and GFS ensemble mean. That means we now anticipate showers and thunderstorms to occur during the afternoon or early evening. The vertical wind shear is forecast to be quite strong; about 60 knots in the lowest 6 kilometers and 30-40 knots in the lowest 1 kilometer of the atmosphere. This would support an organized storm threat; however, instability is expected to be marginal. Both of our high-resolution models seem to indicate that two lines of storms will evolve -- the first associated with a prefrontal trough and the second with the cold front itself. There are even hints that one or two discrete cells will form ahead of these two lines. The biggest threat will be the potential of wind damage because of the strong environmental flow, but the weak instability and richer low-level moisture may be just enough to support an isolated tornado or two. Present indications are that what instability there is will be located along and west of a line from Moultrie to Tallahassee to Apalachicola. Thus, the western parts of our viewing area will have the best chance of strong or marginally severe thunderstorms. We want to emphasize the chance for widespread severe weather is not high, and most areas will see some rain showers and regular storms -- with amounts averaging around one-quarter inch. Locally heavier amounts are probable where the heavier storms end up.

We expect clearing skies behind the system from Thursday through Saturday. The airmass behind this front is not cold, so highs are expected to reach the middle and upper 70s, which is above average for mid to late March.

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