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Wednesday, October 27, 2021

SPC Oct 27, 2021 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1251 AM CDT Wed Oct 27 2021 Valid 271200Z - 281200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN LA... ...SUMMARY... Isolated to scattered severe thunderstorms capable of producing damaging winds and a few tornadoes should occur Wednesday into Wednesday night across parts of east/southeast Texas across Louisiana to the central Gulf Coast. ...Synopsis... Shortwave trough currently moving into the southern Plains will continues east-southeastward throughout the day while deepening and maturing. Surface low associated with this shortwave is currently over northwest OK. The expectation is for this low to move eastward just ahead of the upper trough through the day, before beginning to occlude later this evening. A secondary surface low will likely develop farther south and east (over southeast TX) during the afternoon, progressing eastward across southern LA throughout the late afternoon/evening. ...East TX through Lower MS Valley into the Central Gulf Coast... The line of storms currently extending from central OK southwestward into southwest TX is forecast to continue eastward across southeast OK/east TX this morning and through the lower MS Valley during the afternoon and evening. A very moist airmass will be in place across the Lower MS Valley ahead of this line of storms, with dewpoints likely in the low 70s across much of LA. Despite these moist low-level conditions, warm mid-level temperatures will keep buoyancy modest. In contrast to the modest thermodynamics, low-level kinematic profiles will be quite strong. Consensus among the guidance forecasts around 200 m2/s2 of 0-1 km storm-relative helicity throughout the warm sector preceding the convective line. These conditions will support the persistence of the convective line, which an attendant threat for damaging wind gusts and brief/embedded QLCS tornadoes. Additionally, these conditions support supercells with any discrete warm sector development. Confidence in discrete warm sector storms has increased enough to merit the delineation of a small 10% tornado probability across southern LA. The potential for embedded/QLCS tornadoes also appears to be maximized in this region. This tornado and damaging wind threat will shift eastward into southern MS/AL Wednesday evening and the FL Panhandle Wednesday night/early Thursday morning. Sufficient boundary layer-instability to support surface-based storms becomes more uncertain with eastward extent across these areas, and the line should eventually weaken late Wednesday night. ...Southwest/South-Central AR...Northwest LA... A low-topped convective line may develop Wednesday afternoon across parts of eastern OK/TX into western/southern AR along or just ahead of the cold front. Even though low-level moisture will be more limited across this area, cold mid-level temperatures associated with the upper trough may still support weak destabilization. Strong low/deep-layer shear suggest some threat for isolated damaging winds and perhaps even a brief tornado if the line develops. This threat will lessen Wednesday evening across AR owing to waning instability with the loss of daytime heating. ..Mosier/Squitieri.. 10/27/2021 Read more LIVE: spc.noaa.gov
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