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Gravity Wave/Wake Low in Central Alabama

Posted on: 8:57 pm, January 10, 2013, by

10:00 PM Update:
The gravity wave/wake low event caused wind gusts in North Alabama up to 49 MPH as of 10:00 PM. Here’s a quick run-down:

49 MPH in Claysville
34 MPH in Moore’s Mill
32 MPH in Huntsville (airport)
26 MPH in Scottsboro
25 MPH in Muscle Shoals

Here’s what the wave looked like in the barometric pressure reading at Huntsville International. Notice the little spike in pressure; that’s the compressed, warmed air (the “high”). The wind came as air blew from that high to a low behind it (west of it).

Screen Shot 2013-01-10 at 10.03.01 PM

Huntsville seismologist Steve Jones sent me his seismogram from the evening that actually measured how the breeze caused some minor ground shaking. The wind energy blowing over the ground translates to very small, weak energy waves in the ground (too weak to actually feel, but they can be measured).

Here’s what Steve says:

I’m still seeing some activity in the trace, perhaps from the wave’s impact to areas of terrain east of here…it looks like there were THREE main pulses of winds in the wave’s passage thru Huntsville, with the first being at 8:27 pm, and the last at 9:09 pm.

Steve Jones - Alabamaquake.com

Steve Jones – Alabamaquake.com

Original Blog Post:

An almost invisible weather event is unfolding tonight over Central Alabama: a gravity wave/wake low. These wind events develop behind decaying lines of showers and thunderstorms due to warming and cooling process caused by upward and downward currents of air in the atmosphere:

Screen Shot 2013-01-10 at 8.47.16 PM

The wind blows INTO the wave (like air blows into an area of low pressure) as it propagates east, and those gusts can exceed 40-60 MPH like they have already in the Tuscaloosa area.

Basically, the old storms collapsed causing a strong downward motion in the atmosphere. The air warms and pressure rises when this happens, so it creates a strong pressure gradient over a short distance. Air blows away from the high toward the relative area of low pressure in the “wake” (just behind the collapsed storms), and the stronger the gradient is, the stronger the winds become.

The biggest impact from this wind event will be well south of the Tennessee Valley through the Birmingham metro area. Wind gusts to 30 MPH are still possible east of I-65 in northeastern Alabama through 10 PM.

-Jason
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