1PM Day 1 Convective Outlook for Thursday, February 26. THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE ARKLAMISS EASTWARD INTO WEST-CENTRAL ALABAMA
SUMMARY
Scattered severe thunderstorms capable of large hail will be possible from the ArkLaMiss into north-central Alabama, through early/mid-evening.
20z Update - ArkLaMiss/Deep-South
Based on latest surface observation trends, the Slight risk (level 2 of 5) has been expanded a small amount eastward across portions of west-central AL. Temperatures have warmed into the low to mid 70s amid low/mid 60s F dewpoints. Steep midlevel lapse rates atop the warm/moist boundary layer are supporting a corridor of around 1000 J/kg MLCAPE into west-central AL. This may support stronger/better organized updrafts and a risk for large hail.
The Marginal risk (level 1 of 5) has also been expanded north and eastward across northern and central AL. Trends in CAMs guidance (specifically FV3/RRFS members) suggest a couple of storms may develop further north. Furthermore, RAP forecast soundings appear to be representing the boundary layer well, and suggest any storm moving across northern into east-central AL could produce isolated hail.
For more details on short term severe potential, reference Mesoscale Discussion 119.
Deep South including ArkLaMiss to north-central Alabama
Visible-satellite imagery late this morning shows scattered to overcast cloud cover from southern AR/northern LA eastward into eastern AL. Surface temperatures are gradually warming through the mid 60s into the lower 70s deg F in areas void of extensive clouds, mainly from west-central AL westward.
A mid-level disturbance over the central High Plains is forecast to quickly move southeastward into the ArkLaMiss by late tonight. As the upper system approaches, a cold front draped from southeast OK eastward along the MS-TN border is forecast to accelerate southeastward this evening and through much of the central Gulf Coast states through tonight.
Modest mid-level cold-air advection will continue through the afternoon and steepen 700-500 mb lapse rates across MS/AL. The advection of the mid-level lapse rate plume and additional heating will combine to increase buoyancy (ranging from 1500+ J/kg SBCAPE west, to less than 500 J/kg east). Guidance is consistent in showing weak low-level flow, but strong mid/high-level winds will yield 40+ kt effective shear, supporting the potential for severe storms including some supercells as storms develop and intensify through mid/late afternoon. Both the prospects for appreciable destabilization and probable widely scattered coverage of an initial supercell storm mode, lend confidence for upgrading severe hail probabilities (Slight Risk). A gradual waning in storm intensity is expected through the evening as instability lessens and a transition to less organized storm modes occur.