Saturday Weather Blog: Spring has sprung

By: Meteorologist Ray Hawthorne Email
By: Meteorologist Ray Hawthorne Email

It's a mild and muggy morning across our entire area as temperatures have already climbed into the mid 60s with dewpoints in the lower 60s. A warm front has lifted north of us, and is located on a line from Southern South Carolina to just south of the Atlanta metropolitan area to near Birmingham. An extensive area of low clouds has pushed northward from the Gulf of Mexico behind this warm front. The big question for today is whether these clouds can break up. The morning balloon launch at Tallahassee indicates that the air temperature needs to reach into the lower 70s in order for the drier air a few thousand feet above the ground to make it to the surface. This should happen around noon. Once the breaks of sunshine develop, temperatures will soar into the lower and mid 80s away from the coast on the heels of a gusty southwest wind. The strong pressure gradient between a low in the Tennessee River Valley and a high in the Bahamas will give us sustained winds in the 15 to 25 mph range. Some of the wind gusts could reach 30 or 35 mph.

The other important item of note in this morning's balloon launch was the presence of a capping inversion, or just "cap" for short. The cap is a warm and stable layer that acts to prevent thunderstorm formation. As a warm chunk of air rises from the ground into the atmosphere, it will continue to accelerate if the air surrounding the chunk of air is colder than the chunk of air itself. Today, the air surrounding this theoretical chunk of air is warmer than the chunk itself, so as the atmosphere attempts to make a thunderstorm, it is denied. The near-term model vertical profiles are forecasting the cap to hold pretty strong in North Florida, so this part of our area will have the lowest chance of afternoon or evening thunderstorms. The models are showing a weaker cap toward our far northern counties (those along and north of U.S. Highway 82 in Georgia). As a low-amplitude shortwave trough and cold front approach from the west, the cap is expected to break and lead to vigorous storm development in Central/North Georgia into South Carolina. The high-resolution models that we run here at the station (both WRF and Super Microcast) forecast the storms to weaken as they approach the strongly capped environment in our area this evening. This scenario is also supported by the government-run higher resolution computer models. In addition, I am encouraged by the New Orleans and Birmingham morning data, which are showing even stronger caps and lending credence to the forecast models. That said, I encourage those especially in the Albany, Tifton and Sylvester areas to keep a close eye on things this evening -- just in case. If the cap somehow breaks, the environment would be quite favorable for extremely large hail (golfball or baseball size) and damaging winds. This is a conditional threat and seems unlikely to me at this time.

The surface "cold" front is expected to pass quickly through our region between midnight (far northwest counties) and sunrise (far southeast counties). Our winds will shift from the southwest to the northwest, acting to usher in drier air into the area. Dewpoints should fall into the 40 to 45 degree range on Sunday, making for a very pleasant day under abundant sunshine. The air does not look dramatically cooler behind this front. In fact, with an offshore flow and dry air, temperatures could again test 80 degrees in the afternoon.

Monday and Tuesday look like fine days. Highs are expected to reach near 80 degrees away from the coast under mostly sunny to partly cloudy skies. Morning lows will be in the low to mid 50s.

The next storm system -- now located off the West Coast of the U.S. -- is expected to swing through Texas on Tuesday and reach us by Wednesday. There is very strong agreement between the operational global models and their ensembles on this scenario. There are the usual timing differences, but they are fairly subtle for 5 days out. The ECMWF and UKMET models are a little slower than the GFS and Canadian global models. This forecast will lean toward the ECMWF and UKMET, which have had the most robust verification record over the past few months. Thus, I expect an increasing likelihood of showers and thunderstorms during the day on Wednesday. There will also be the possibility of severe weather. That will be addressed in later blogs and forecasts, so stay tuned.


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