Thursday, May 31, 2012

Severe Weather Threat Ahead of Cool Front Today...

Severe thunderstorms are forecast across a broad region today, ahead of a slow moving frontal boundary. The risk of severe weather is present throughout the yellow shaded area on the above image, from the Midwest and Ohio Valley, Southwestward into the middle and lower Mississippi Valley and central through southern Texas.

In general, severe thunderstorms are forecast during the afternoon and evening hours, primarily after 2pm, as the atmosphere heats up and becomes unstable ahead of the frontal boundary.  This instability will interact with several disturbances in the upper-atmosphere to produce strong to locally severe storms in this region.

Large hail and damaging wind gusts are the primary threats across this region today.  While an isolated tornado or two cannot be ruled out, this threat is not "high" in any particular area.  A localized tornado threat would be greatest in association with any thunderstorm that is able to remain isolated and become well organized, generally within the first 1-3 hours of development.

There is a heightened risk of damaging wind potential across portions of the Ohio and Tennessee Valley, into the lower Mississippi Valley, within the red shaded area on this image:

There is also a "conditional" risk of particularly large hail, in excess of 2 inches in diameter, with any storms that form within the black hatched region in Texas, as shown on the image below:

I note that the very large hail risk is "conditional" in southwest and southcentral Texas because first thunderstorms must develop in order for this threat to be realized.  Coverage of thunderstorm activity is only expected to average 20-30% across this region, mainly due to the presence of a strong capping inversion.  While there is only a 20-30% chance of a thunderstorm occurring in this region, there is a near 100% chance that severe weather will take place in association with any storm that does develop.

Folks living across all of the above mentioned severe weather threat areas should remain alert today.  Listen to NOAA Weather Radio, local media or another trusted source for later statements and possible warnings.  Please take a few moments to familiarize yourself with your best sheltering option, and be prepared to move there quickly if threatening weather is observed or a warning is issued for your area.

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