SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0136 PM CST Thu Feb 11 2021 Valid 112000Z - 121200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Appreciable risk for severe weather is unlikely across the U.S. today. ...Southeast Louisiana into Georgia... A batch of thunderstorms extends from southeast LA into southwest AL as of 20Z, with periodic bowing structures noted earlier across southern MS. These storms are currently near the MLCAPE axis with 500-750 J/kg, and may be already peaking in intensity. Large-scale ascent is forecast to decrease later today, with storms also encountering weaker instability. Until then, a few strong wind gusts cannot be ruled out. ..Jewell.. 02/11/2021 .PREV DISCUSSION... /ISSUED 1030 AM CST Thu Feb 11 2021/ ...Discussion... Broad/low-amplitude cyclonic flow aloft within the polar stream will persist through the period, south of a strong/cold upper low residing over the Canadian Prairie. Meanwhile in the southern stream, weak perturbations will move eastward across Texas and the southeastern states, ahead of a larger short-wave trough moving into/across Mexico. At the surface, cold air continues to spread southward out of Canada, affecting a large portion of the country east of the Rockies. A baroclinic zone separating the polar air from the lingering/higher theta-e southern U.S. airmass is currently stretched from the Carolinas southwestward to the western Gulf of Mexico. This front will sag slowly southeastward with time, as cold air advances. Moderate mid-level flow is observed atop the higher theta-e airmass across portions of the Southeast. However, abundant cloud cover will continue to retard any appreciable heating, keeping the boundary layer slightly stable in most areas and limiting available CAPE to generally only a few hundred J/kg at best. The modest instability, combined with relatively weak flow in the lower troposphere, suggests that despite locally gusty winds, storms should remain sub-severe. As such, the MRGL risk over portions of northern Georgia and into South Carolina is being removed at this time. Farther to the southwest, into eastern Louisiana and southeastern Mississippi, a small area of greater low-level moisture is indicated southeast of the surface cold front -- supporting mixed-layer CAPE in the 500 to 1000 J/kg range. However, with modest shear, and storms expected to shift through this small zone of slightly more favorable thermodynamics over the next couple of hours, risk for any more than a briefly stronger updraft appears unlikely, and thus will not introduce MRGL risk across this area. Elsewhere, severe storms are not expected across the CONUS.
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