Saturday, April 27, 2013

Severe Weather Targets Plains This Evening

A slight risk of severe weather has been issued by the Storm Prediction Center for today, April 27th. This risk covers the states of Texas, Louisiana, Arkansas, Mississippi, Alabama and Tennessee.

Current frontal analysis shows the storm system of interest currently crossing over into western Arkansas. Warm front extends through the middle of Arkansas and cuts through central Mississippi, while a trailing cold front is draped across Texas. High precipitable water values shown in green indicate the warm front is doing its job in transporting energy and warmth up from the Gulf of Mexico, adding fuel to the fire that will start this evening in the states mentioned above. The storm system appears to be pushing northeast, and this should allow the warm front to pull the warmth and moisture north to encompass the rest of the states expected to be under a threat for severe weather tonight.

Short range NAM model predicts surface-based instability to be in excess of 3000 j/kg in some spots, with little to no capping inversion in the slight risk area. Thunderstorm formation is anticipated to be consistent with a damaging wind/hail risk. Elevated helicity values combined with this excessive instability should allow for an isolated tornado threat, especially in eastern Texas into southeast Arkansas. Relatively lower instability values will be present towards the easternmost portion of the slight risk area in Tennessee. I believe that we will see thunderstorms fire in that area, although the comparison of Tennessee's instability and the 3000 j/kg in Louisiana tells me the storms in TN will not be as significant as those in the Gulf Coast states.

At the present time... latest upper air soundings reveal a fairly substantial capping inversion stretching from the Gulf Coast into Louisiana and Mississippi. Not concerned with this development, as lower level stability is normal in the mornings. The sounds analyzed with that lower level layer of stability were mainly outside of the 3000 j/kg belt shown above, and the one sounding within that belt had a rather weak stability layer. Upper and mid level wind fields have a streak of slightly enhanced winds on the south flank of the storm system, and these winds should fall along the slight risk area later on this evening.

Storm Action Day status: A Storm Action Day will NOT be declared today.