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Posted at 11:34 AM ET, 01/27/2012

Yes, that big boom was late January thunder

Weather map shows cold front moving through region at 10 a.m. (National Weather Service)
More than one deafening crash from the heavens jolted the metro region this morning. The noise was so loud, jarring, and out of season, some did not immediately think “thunder” when they heard the clamor, but were concerned it might be something else, like a blown transformer, a plane crash, a sonic boom, or a bomb. Rest assured, it was thunder. Here’s what happened...

A warm front moved through overnight and very warm, moist unstable rushed northward, pushing temperatures above 60 degrees. This morning, a dynamic cold front collided with this unseasonably mild, juicy air. The result: a line of springlike showers and thunderstorms.

The volume of the thunder may have been enhanced a little due to something called “elevated instability”. We get elevated instability when temperatures aloft warm more quickly than temperatures at the ground, creating an inversion (normally, temperatures cool with height). The Weather Channel’s severe weather expert Greg Forbes explains:

What makes thunder louder on some occasions than others? Most of the time it has to do with how the temperature changes with height. The short answer is that thunder tends to be loudest when there is a cold pocket near the surface and warm air above it -- an “inversion.”

The remains of a temperature inversion from last night might have amplified the sound of the thunder that developed in this morning’s thunderstorms. Graphic from Unisys weather, adapted by author.
This morning, the temperatures of around 60 degrees near the ground weren’t exactly “cold”, so this was by no means a classic case of elevated instability. However, warm air aloft had arrived more quickly than at the surface overnight, and the morning temperature profile shows the remains of an inversion (the inversion had been much stronger 12 hours earlier).

When you have such an inversion, the sound of thunder can get trapped in that inversion layer, making it louder.

Was the thunder unusual?

Thunder in January around Washington, D.C. is not common, but certainly not unheardof. Particularly during La Nina years like this one, strong cold fronts with very mild air out ahead of them occur during the winter, setting the stage for possible thunderstorms.

By  |  11:34 AM ET, 01/27/2012

Categories:  Latest, Thunderstorms, Science

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