Ann Arbor’s Deep Freeze Explained

 
 

It’s -5 degrees right now and not getting higher than 12-degrees for a high-temperature today.

Forecast for the next seven days is a high temp in the teens and lows mostly in the negatives according to my trusty Weatherbug App. The only exception is Thursday’s high will be a relatively balmy 21-degrees. All before figuring in wind chill.

What turns the bone-chilling cold of a normal Michigan winter into a sinister bone-snapping cold? It’s dangerous out there! Blame it on normal Radiational Cooling throwing a holiday party for three friends: Clear Skies, Light Wind, and Dry Air.

First, the stage is set through the normal heating and cooling of the air. Everything radiates heat. For our example, the earth gives off heat but also receives energy from the sun which it converts to heat. During the day, incoming solar energy exceeds outgoing earth’s radiational heat release and the temperature of the ground surface rises. At night there is no incoming solar energy but the ground continues to release heat and without any input, the temperature falls. This is radiational cooling.

Makes sense. We’ve always known the days are warm because the sun is up. But there are cold nights and then there are these re-he-he-he-ally cold nights. Why?

Radiational Cooling wants to break up the daily routine and invites in Clear Skies, Light Wind, and Dry Air which bring their gifts to the party. Clear Skies chases away cloud cover which is to the earth what a layer of clothing is to the body. It keeps the generated heat close. Remove the layer and the heat escapes.

Light Wind confines the cool, clear air preventing it from mixing with warmer air. Think of a cyclonic weather pattern that circles the wagons, so to say, protecting the cold air. Dry Air reduces the water content of the air (humidity) which makes the atmosphere around the earth warmer than outer space. The moisture radiates the heat back to earth. Dry Air has less reflective ability.

So that’s it. We’re all stuck waiting for the unwanted party guests to leave. Given the choice, I’ll take this cold over the 58” of snow (and still counting) Erie, PA experienced over the past two days. What I really want however is C) None of the above.

Story by: Doug Marrin

Cover Photo: Kelly Boyes

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