Physics of Arctic air

It’s mighty cold outside today, with temperatures at mid-afternoon below freezing most places north of a line from Gadsden to Warrior. With the wind blowing, mountain tops are even colder…it’s 29 on the mountain in Clay NE of BHM, 30 on Mt. Cheaha, and 23 in Mentone. Wind chills all around are 15-25, and will drop into the single digits this evening.

This cold air is moving in fast on strong northerly winds. Luckily, the snow cover has backed off some in the past few weeks, and we had mild temperatures in much of December, helping the ground to warm up. This is allowing the cold air to modify a good bit as it comes south, absorbing heat from the ground.

Here are the trajectories of the air that will be in BHM, HSV, and MOB this afternoon at 3 pm. These show where the air that is here now started 36 hours ago, and how it got here.

The air in BHM now started in western Wisconsin at 3 am yesterday morning. It was then near Prairie Du Chen, WI at noon yesterday, Peoria, IL at 6 pm yesterday, NW of Evansville, IN at midnight, in Nashville at 6 am today, and Cullman at noon. If you follow the surface temperature of the air over us now, over the past 36 hours, you can see it has warmed quite a bit on its way south.

It started out at -5, warmed a little (into the single digits) over Illinois yesterday, into the teens over southern Illinois, Kentucky, and Tennessee overnight, then rapidly into the lower 30s over southern Tennessee and north Alabama today, with southern sunshine.

However, as the ground cools to our north, and the sun goes down, the air will get modified less as it comes south, so temps will drop well into the teens tonight, and likely stay a degree or two colder tomorrow than today.

Remember, if you haven’t already, drain or cover outside faucets, bring in the pets (or, if you absolutely can not bring them inside, put sweaters or something on them, face their doghouse door south, etc., as mentioned in detail in earlier blogs), check on the elderly, and put towels around any drafty doors or windows in your house.

Category: Uncategorized