The strongest cold front to push through the southeast since last spring will sweep through Friday into Saturday morning, bringing strong to severe storms and big time cool down.
IMAGES BY ALLAN HUFFMAN OF AMERICANWX
THE 500 MB PROCESS
You can clearly see the strength and magnitude of this storm by looking at the 500 mb voriticty. This is a very deep trough and upper level low that will be providing energy to the cold front. Here is the progression of the upper level low from Thursday to Saturday as shown on the GFS computer model.
Thursday 2:00 p.m.
Friday 2:00 p.m.
Saturday 2:00 a.m.
Saturday 2:00 p.m.
You can see the upper level trough will be moving very quickly, which will help to limit the amount of rain in the forecast. What is important to note is how the upper level trough takes a negative tilt as it moves northward Friday. This can help to cause very strong to severe storms to develop ahead of the surface front and along the surface front.
2:00 p.m. Friday
The GFS also shows very high levels of moisture transporting northward Friday. The winds at 850 mb (5,000 feet) are forecasted to be coming from the south at 40 mph, so this will cause very strong winds in the mountains of North Carolina and Virginia. This will provide copious amounts of moisture for the storms along and ahead of the cold front. By Saturday at 8:00 a.m., the GFS has the front pushing off the coast and the best moisture off the East Coast by Saturday at midday.
JET STREAM AND IT'S IMPACT
There will be very strong upper level divergence due to the jet stream at 250 mb. The GFS shows a 100+ mph jet moving just north of the area, and we will be in the favorable right entrance of the jet Friday afternoon. This will help to increase upper level divergence, aiding the development of showers and storms.
WHAT TO EXPECT
As you can tell, this is going to be a very powerful system. I expect a line of thunderstorms to enter the mountains around midday Friday and begin sweeping across the piedmont of NC by Friday evening. This could cause havoc for high school football games through the southeast Friday night with the strong storms pushing through. The front will continue to march eastward through the overnight hours, and then will exit the coastal areas Saturday morning.
The greatest threat with this front will be strong storms producing very strong winds. Winds ahead of the front will be 15-20 mph from the south, and you will notice the very humid air ahead of the system. As the storms pass through, strong winds will be possible. In the strongest storms, winds could approach 50 mph. Behind the front, winds will turn and come from the northeast. This will allow for rapid drying behind the front.
The severe weather threat will become more evident as we move forward, and the specific threats will be better known by Thursday. I will post an update describing what to expect on Thursday evening.
As for rain, I am expecting widespread 1/2 of an inch to an inch of rain from the front. Some areas could receive higher rain totals where the strongest storms. This storm is not expected to be a big rain producer, so flash flooding is not anticipated at the moment.
BEHIND THE FRONT
Behind the front, temperatures will struggle to reach the low 70s across a large part of the southeast United States. The GFS is even indicating some areas may struggle to reach the low 60s north and west of I-85 despite abundant sunshine. Coupled with these cool temperatures will be super low dew points (20-30°F) and low humidity values (10-20%). Winds will also be around 10-20 mph with gust up to 30 mph outside the mountains, making it feel even cooler than what it is.