Severe weather analysis - March 7, 2012
Thursday March 08, 2012
Not much is going on across the lower 48 after Friday's destructive tornado outbreak. However, a faint potential exists for some severe weather across portions of the Arklatex as well as perhaps northeastern Texas and extreme northwest Louisiana. Should this occur, it would be on Thursday. This is reflected in the thoughts of the Day 2 Convective Outlook recently issued by the Storm Prediction Center (SPC) in Norman, Oklahoma:
Figure 1. Latest Day 2 Convective Outlook issued by the Storm Prediction Center (SPC) in Norman, Oklahoma. Forecast valid from 1200Z Thursday March 08 to 1200Z March 09, 2012. For translational purposes, 1200Z would be 8:00 AM central standard time (CST).
The catalyst for this weather will be a developing mid- to upper-level trough now seen on water vapor imagery approaching west Texas. This trough is forecast by the reliable global and regional models to become positively-tilted as it gradually progresses eastward. There is already evidence of this happening on the aforementioned imagery. Although warm air advection (WAA) ahead of this system will be fairly large, with at least lower to mid 60s (F) dew points possible across the Arklatex and lower Mississippi Valley on Thursdasy, upper air soundings within the slight risk area indicates that a substantial mid-level capping inversion exists directly above this layer of abundant moisture in the lower troposphere. This cap is not forecast to break significantly during the day on Thursday. This, along with the likelihood of a pre-frontal linear band of convection/weak squall line, suggests the tornado threat is minimal. The primary threats instead appear to be damaging wind gusts and/or large hail.
In comparison to other severe events, and certainly compared to Friday's historic event, the severe weather threat with this system remains marginal at best.
Farther south, the inversion will be even greater, curbing the potential for significant destabilization within the pre-frontal warm sector. However, this trough is forecast to effectively stall over the western Gulf beyond Thursday/Friday, which could lead to a several day period of heavy rainfall. This could help to alleviate the ongoing drought across Texas:
Figure 2. Latest Texas drought map (February 28, 2012) as provided by the US Drought Monitor.
By Sunday/Monday, another significant perturbation within the belt of mid-latitude westerlies is forecast to move eastward and then east-northeast across the lower to middle Mississippi valleys. Not only does predictability remain expectantly low for this next system, it is likely that the several day period of cloud cover/heavy rains associated with the aforementioned system will preclude appreciable destabilization/vertical instability ahead of the cold front.
In short, no significant severe weather events appear likely for the next week or so, the isolated event on Thursday notwithstanding.