We here in the Southeastern U.S. are already in a cold air mass…with 4 pm tempertures mainly in the 30s and 40s from Arkansas to the beaches of Alabama and NW Florida to the Carolinas. Here in Birmingham, the temperature has remained steady near 37 F all day, with wind chills between 15 and 25 F. So yes, it is already cold! After dropping into the 20s the next two nights over much of the Southeast, it will start to warm up a bit by Wednesday and Thursday.
It is true that we have had no serious, bitter cold outbreaks here in the Southeast since early 2018. Below is a chart of freezing degree hours at Birmingham airport for each Winter since 1980. This number was calculated by multiplying the number of degrees below freezing, for any hour with a temperature of 32 or below, by the number of hours that temperature occurred. 3 hours at 25 F would give us 24 freezing degree hours (FDH), 3 hours a 32 F, 3 FDH. Note the lack of FDH in the Winters of 2019 and 2020 (each winter includes Nov of the prior year through April of the year shown). Note the last two Winters, and 4 of the last 5 (going back to 2015-16), have been relatively mild in terms of freezing, bug killing, ground crackling cold.
That may be about to change. This Winter so far has been chilly, with very few “warm” days (enough to play golf) and a lot of cold fronts bringing nightly temperatures in the 20s and 30s. But, we still have not seen a true Arctic blast yet. It looks like it may be coming next week. A large mass of extremely cold air has pooled in northern Canada and the Arctic Ocean, as shown in the 3 pm temperature analysis below. Much of the circled area is in the -30s and -40s F.
And, the upper ridge that has been persistent for over a week in the Pacific will start to push eastward this week, allowing very high surface pressures (typically associated with heavy dense cold air), and a deep upper trough to help push the cold air south toward the CONUS.
By Friday evening, the bitterly cold air mass will already be pouring into the northern Plains of the U.S., with the northerly flow being pulled by a large low pressure area over the Great Lakes, and pushed by a massive 1050 mb surface high pressure area in western Canada. By this time, according to computer models, temperatures below zero will already be as far south as Fargo and Minneapolis. but the northerly flow, the upper-level dynamics supporting it, and the simple weight of the extremely cold dense air, will help it continue to push south over the weekend.
The Arctic front should, according to multiple consecutive runs of the American GFS model and the European ECMWF model, push through the Southeast Saturday night and Sunday, bringing high winds and bitterly cold air, with wind chills below zero on Sunday as far south as Birmingham, Nashville, and Atlanta. By Monday morning at 12Z (6 am CST), the cold air will be fully entrenched over the Southeast and the eastern U.S. The map below shows air temperatures, not wind chills, in the teens all the way down to Jackson, MS; Montgomery, AL; and Macon, GA, with single digits in Huntsville, Nashville, and the northern suburbs of Atlanta. Note the temperatures as low as 30 below from ND into MN, WI, IA, and IL.
An air mass this cold will come in with strong winds (as they almost always do). Wind chills will be extremely cold for an extended period. Lows could reach the single digits Monday night of next week as far south as Birmingham and Atlanta, making it the coldest night in 3 years. Below I have plotted the model forecast temperatures for next weekend and early next week from the GFS and ECMWF models at Bluff Creek, AL, about 20 miles west of Birmingham. The graph starts Saturday at 12:00.
The computer models differ on just how cold it will get, but both keep temperatures below freezing for a continuous 24 hour period, and the models have gotten more aggressive with the cold air since yesterday. The computer models indicate another shot of cold air later next week, and a possibility of some snow. But, that is over a week away, so confidence is low. Either way, we have gone into a very cold pattern that will last at least the next couple of weeks. Think about insulating pipes and the usual cold precautions. And don’t let pets stay out in the extreme cold…it is often 3 or 4 degrees colder near the ground on a clear cold night than it is at 6 feet up. Bring them into the basement, garage, or inside the house!
Dr. Timothy A. Coleman
Coleman and Knupp, LLC