Severe weather analysis – 915 pm

…Severe thunderstorm watch until 4 am…

Interesting weather situation developing overnight.  A HUGE surface low pressure area, centered over 1,500 miles to our NW, covers much of the US tonight (see map below), with frontal boundaries and upper-level disturbances in the SE US.  The main action is near the front right now, from middle TN across MS, AR, and east TX, and the storms appear to be forming in wave-like patterns, spaced about 100 miles apart (see radar above).

Scattered storms will continue to develop over the next 2-3 hours due to warm air moving in and causing upward motion, and with cold upper-level temperatures, hail is the main threat.  Severe thunderstorm warnings will liekly be issued.

What we are more concerned about is the time after midnight.  Dewpoints over south Alabama are in the upper 60s, and this warm, humid air will move north underneath cooling upper-level temperatures.  CAPE values (instability) will rise from near zero now to over 1,000 J/kg over western and central Alabama by 3 am.  This, combined with moderate wind shear (helicity 200-300 m2/s2), will allow for the possibility of rotating storms and isolated tornadoes, mainly between midnight and 8 am.

This is a night where you should leave a NOAA weather radio turned on if possible (I know it’s tempting to unplug it when it keeps going off for severe thunderstorm warnings, but be patient, the NWS is doing its job).  Go ahead and have a plan for quick action if a tornado warning is issued.  Remember, lowest floor of your home, interior room, away from windows and doors, get low and protect your head.  If you are in a mobile home and a tornado warning is issued, leave it and go to a building immediately.

We are not talking about a major tornado outbreak here, but even one tornado is dangerous.  The largest threat will be west of I-65 through 3 am, and over the whole area after that.  If you live in the BHM metro and just can’t stand it and unplug your weather radio, you could set an alarm around 2 or 3 am to check the weather situation, and if a tornado watch or any tornado warnings are in effect, plug it back in.

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