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Severe Weather Update 905 pm

| October 18, 2007 @ 9:03 pm | 24 Replies

Storms have really increased in coverage and intensity over the past couple of hours, with a line of severe storms currently just ahead of the cold front, from Louisville, Kentucky to Oxford, MS into extreme NE Louisiana. Sometimes, after dark the friction with the ground that slows the wind down during the day decreases just a bit due to cooling near the surface, enhancing convergence and storm development.

The air is very unstable and the wind shear is very high in the area ahead of the front from middle TN across MS and AL. Looking at the Birmingham balloon data from 00 UTC, there is a slight warm-air cap (see below) between 800 and 700 mb, which may have limited storms in our area so far today. But, with the upper-level dynamics approaching, the air will be lifted and cooled, eliminating most or all of that cap over the next few hours. The persistent rain area has stabilized the air more over southeast Alabama. But, in areas like HSV, TCL, BHM, GAD, and ANB, the air is unstable, and any low-level cooling will likely be offset by upper-level cooling, keeping the air unstable enough for storms through the night.

bmx.PNG

The main line of storms should not arrive in NW AL until 11 pm or so, and in Birmingham after midnight. The main threat with those will be damaging straight-line winds, but isolated tornadoes are still possible. Storms that are of more immediate concern have formed ahead of the main line in eastern Mississippi, approaching Pickens and Sumter counties. These are out by themselves, and carry a tornado threat.

As we’ve been saying all day, keep your NOAA Weather Radio on standby if you go to bed tonight before the storms get here.

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