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An Update on Tonight’s Severe Weather Threat

| December 28, 2016 @ 2:00 pm

We continue to monitor a severe weather threat for the northern and central parts of Alabama for the overnight hours tonight.

An approaching upper level trough will power a cold front that will move through the state tonight and trigger showers and thunderstorms.

The strength of the trough along with some decent thermodynamic parameters are producing the severe weather threat.

SETTING THE STAGE
Our strong upper trough is dropping through the Dakotas and Nebraska this afternoon. A surface trough extends from west of Chicago to west of Dallas. A weak surface low is over southern Missouri. A warm front is lifting through Central Alabama at this hour, separating warm, humid air to the south from drier, slightly cooler air to the north. Up at the jetstream level, a split flow pattern is over the U.S. setting up an area of upper level divergence right over the Arklatex. This divergence will spread eastward tonight putting Alabama in a very favorable region for storms to intensify.

SEVERE WEATHER PARAMETERS
Instability will be present tonight as the airmass with dewpoints in the lower 60s is overspread by colder temperatures aloft, setting up the potential for good upward motion. CAPE values will be in the 500-800 joules/kg range after 9 p.m. tonight for areas south of the warm front. Shear will be ramping up this evening, with 0-3 km helicities soaring to over 200 m2/s2 and peaking over 300 m2/s2 before dropping again after midnight.

SUPERCELLS
There are signs that some discrete thunderstorms will be able to form ahead of the main cold front in the warm sector that sets up. These will have a damaging wind threat and we can’t rule out an isolated tornado or two.

SQUALL LINE
A squall line will sweep through the state during the hours after midnight. Damaging winds and an isolated tornado will be possible with this line of thunderstorms.

TIMING
It appears that the greatest threat for severe weather will be between 9 p.m. and 3 a.m. for Tuscaloosa, Hamilton, Jasper, CUllman and Birmingham and between 11 p.m. and 5 a.m. for eastern sections around Anniston and Gadsden.

BE READY
Review your personal severe weather safety plan and make sure that you have a way to receive warnings after you go to sleep tonight. If you are in a mobile home, know where you will go when a storm is headed your way that could be severe. Pay attention to the radar and our updates.

RAINFALL AMOUNTS
Precipitable water values will approach 1.5 inches tonight, which is high for late December, so rainfall amounts should be decent. Most folks should receive around one half inch tonight. We will take it.

FREQUENT UPDATES
AlabamaWX is in severe weather mode for tonight. Scott Martin and I will have frequent updates throughout the afternoon, evening and overnight. Expect the next update by 5 p.m.

Category: Severe Weather

About the Author ()

Bill Murray is the President of The Weather Factory. He is the site's official weather historian and a weekend forecaster. He also anchors the site's severe weather coverage. Bill Murray is the proud holder of National Weather Association Digital Seal #0001 @wxhistorian

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