Monday, March 7, 2011

Severe Weather Likely Tuesday Afternoon & Evening

Severe thunderstorms are expected across portions of the Southern Plains and lower Mississippi Valley from Tuesday afternoon into Tuesday night.  Below is the severe weather risk area (outlined in green) from the SPC:

For the set-up, take a look at the latest surface weather map as forecast by the HPC, valid 6pm CST Tuesday evening:

As you can see in the above image (click to enlarge), a cold front is forecast to be advancing Southward through the western portion of the risk area by late afternoon.  A dryline will extend Southward from an area of low pressure over northcentral Texas.  At the same time, a warm front will be advancing Northward through the heart of the severe weather outlook area.  At the same time, a strong disturbance will be moving across the region in the middle and upper levels of the atmosphere.

The most unstable air will reside immediately South of the warm front and East of the cold front and dryline, over east-central and northeast Texas into much of Louisiana, western Mississippi and southern Arkansas.  This is where the most violent thunderstorms (assuming they are able to develop*) are likely to occur, with "significant" tornadoes possible (as per the latest SPC discussion - issued at 11:35 am CST today).

*I say, "assuming they are able to develop" because a strong capping inversion will be in place across the same region.  A capping inversion simply means that there is a layer of relatively warm air in place above the surface layer.  This forms a "lid" or "cap" in the atmosphere, which tends to inhibit thunderstorm development.  If clouds in the area are able to develop sufficiently to break through the cap, violent thunderstorm development will result.

Elsewhere, more widespread thunderstorms (some of which could become severe with large hail, damaging winds and isolated tornadoes) are likely along and North of the warm front, and East of the cold front, from the Eastern half of Oklahoma into much of Arkansas and southern Missouri.  It will be easier for thunderstorms to develop in this area because the capping inversion will be weaker (or in some cases, non-existent).

Residents across all of the severe weather outlook (and adjacent) areas should remain alert Tuesday afternoon and night, and listen for later statements, watches and possible warnings.

For our meteorologically inclined readers, below are the latest GFS Model forecast maps for the surface, 850mb (low-level) and 500mb (mid-levels), respectively.  All forecast images are valid 6pm CST on Tuesday evening:

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