It's great to be back from vacation! I am well-rested and that's a good thing because we're in a more active pattern now than when I left.
The morning upper air maps are showing the eastward progression of several low-amplitude disturbances across our area. Even though the air near the ground is cool and stable, there is warm air advection a few thousand feet above the surface. The combination of these two elements is creating a broad zone of lift, which is responsible for the rain this morning. The balloon launch from Tallahassee depicts a completely saturated column between the surface and about 10,000 feet, but the air above that is starting to dry out. This drying trend is more pronounced in the mid and upper layers of the atmosphere at Jackson, MS and Birmingham, AL. In order to introduce ice crystals into a cloud, the atmosphere typically needs to be saturated at temperatures colder than -10 degrees Celsius. Since the air will be gradually dry out in the middle troposphere (where the temperature is colder than that -10C threshold), precipitation processes in the cloud will be significantly inhibited and all of the models agree that most of the significant rains will come to an end by early afternoon. We will just see pockets of drizzle or light rain thereafter. Temperatures should get no higher than the lower or mid 50s and it's entirely possible that a few locales will fail to breach the 50-degree barrier today.
The clouds will break up from northwest to southeast tonight and skies ought to be mostly sunny on Sunday. Despite a northwest wind between low pressure off the Mid Atlantic coast and high pressure building in from the west, temperatures should have no problem reaching the 60s under the abundant sunshine.
The weak high pressure is expected to build overhead Sunday night, so the skies should be clear and the winds will become calm, leading to ideal radiational cooling. Lows will plummet to around 30 degrees by sunrise and we are looking for a 1 to 3 hour light freeze away from the coast and downtown. The overall airmass is not particularly cold, so additional sunshine on Monday will cause our temperatures to rebound well into the 60s. We could even be near 70 degrees by the time we get to Tuesday.
The pattern gets awfully interesting (to say the least) between Tuesday night and Friday. We will be watching two weather systems. The system bringing the tremendous rain and snow to California this weekend is expected to kick out into the midwest on Tuesday and the Mid Atlantic and Northeast U.S. by Wednesday. The trailing cold front should barely be able to make it through here between Tuesday night and Wednesday morning. Since the strongest dynamics will lift to our north, the front will probably just produce some showers for us. It's the second system I am very concerned about. The global models and their ensembles are in outstanding agreement in forecasting a strong middle and upper-level trough swinging from Texas and Mexico on Thursday into the deep south on Friday. The ECMWF model -- the most reliable in the extended period -- is the scariest. The surface low pressure is expected to track from the northwestern Gulf of Mexico to the Tennessee Valley region. Very strong lift and intense deep-layer wind fields are predicted by the numerical models. Provided adequate instability, a significant or even major severe weather outbreak would be anticipated. It's certainly possible the models will change their minds between now and then, but confidence is higher-than-average about this scenario unfolding somewhere in the deep south. We may be implicated in this. As details become clearer regarding instability, we will begin to refine the severe threat and hopefully get a better idea as to which areas will have the best threat of dangerous weather. Stay tuned.