Almost our entire viewing area is starting off with sunshine this morning, but clouds are increasing rapidly to the west of the Apalachicola River. The sunshine will gradually fade behind these clouds this afternoon. Heavy rain is ongoing over the western Gulf of Mexico and eastern Texas, but scattered showers extend as far east as Louisiana and Mississippi. An area of low pressure is analyzed at the surface east of Corpus Christi, TX, with a warm front lying across the southern Gulf of Mexico. We should stay dry today thanks to high pressure nosing in from the northeast, which is supplying us with some dry air. The biggest forecast challenge in short-term is the threat of rain late tonight and Sunday morning. The new NAM model is just rolling in and is showing very little measurable rainfall between now and Sunday. The early morning GFS and local WRF models are not spitting out all that much either. Meanwhile, our RPM model is quite aggressive. It develops a decent shield of light to moderate rainfall from about the Thomasville to Tallahassee corridor and westward toward daybreak. The rain shield (according to the RPM) lifts out of our Georgia counties by midday. The strongest warm air advection is forecast to occur well to our west, but weak warm advection in the lower troposphere should be enough to generate a few light showers mainly in our western viewing area. That said, it's hard for me to accept the very wet RPM since the better dynamics and kinematics should be well to our west. Bottom line: if you receive any rain tonight, don't expect it to amount to very much.
A warm front will be lifting northward from the Gulf of Mexico and should clear all but our far northern viewing area by late Sunday afternoon. Other than scattered showers, it's difficult to predict any meaningful rainfall when the primary lifting mechanism in the atmosphere remains to the west. I suppose any rain is better than none at all. Temperatures should rebound into the 70s behind the warm front, especially in Florida. It should stay a little cooler north of U.S. Highway 84 in Georgia.
Our best threat of rain (and it's not a slam dunk either) should come on Monday. A vigorous upper trough now in the Southwestern United States is forecast to swing northeastward toward the central and lower Mississippi Valley. It will then lift out toward the eastern Great Lakes Monday night. This is a clear indication that the strongest large-scale vertical motion will occur in the western Big Bend, Southwest Georgia and Alabama. Since lift is required for rain, this is where the highest chances will be. The SREF (Short Range Ensemble Forecast) mean is showing greater than a 50 percent probability of weak to moderate instability developing from roughly Tallahassee and Thomasville westward, then tapering to a 20-30 percent chance of the same instability in the Suwannee Valley. The vertical wind shear in the lowest 6 kilometers of the atmosphere is expected to be strong enough to support a few rotating updrafts (i.e. supercells) within a broken squall line as it moves west to east across our area. Since the instability is expected to decrease east of Tallahassee, I expect the squall line to fall apart somewhere in our viewing area, but it's impossible to say exactly where at this time. What I can say is the highest probability for strong to severe storms will be in our western viewing area, with those probabilities lowering the farther east you go. The primary threats with any severe thunderstorms that develop will be brief tornadoes and damaging winds.
The cold front will pass Monday night, but the air is not terribly cold behind it. Highs should still reach the mid 70s Tuesday and Wednesday. The models are hinting at another cold frontal passage around Thursday, but significant rains do not look terribly likely with its passage.