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Monday, May 17, 2021

SPC May 17, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0255 PM CDT Mon May 17 2021 Valid 172000Z - 181200Z ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS THE TEXAS SOUTH PLAINS/WESTERN NORTH TEXAS AREA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL HIGH PLAINS INTO THE SOUTHERN PLAINS REGION... ...

SUMMARY... Severe thunderstorms remain likely across the southern Plains this afternoon and tonight. The potential for very large hail, a few tornadoes, and damaging winds will be focused across a broad part of west/northwest Texas. ...Discussion... Forecast areas and reasoning laid out in prior outlooks continue to adequately reflect current expectations overall, with respect to the evolving severe weather scenario. As such, little change to outlook lines is required at this time. The main exception is over southern Louisiana, where small/rotating cells persist near and east of a small mesolow in the vicinity of Calcasieu Lake, with at least one brief tornado reported. Given ample low-level shear, the very moist boundary layer, and presence of the mesolow, sufficient risk for additional/brief tornadoes warrants SLGT risk upgrade in this area. For additional short-term information, please refer to SWOMCD #652. Otherwise, aside from a slight westward expansion of 5% wind/2% tornado probability in north central New Mexico, no other substantive changes appear necessary to the current outlook. ..Goss.. 05/17/2021.


PREV DISCUSSION... /ISSUED 1138 AM CDT Mon May 17 2021/ ...

West/southwest/north Texas and southwest Oklahoma... An active severe-weather day is expected particularly across west/southwest Texas later this afternoon/evening. In the base of an eastward-moving upper trough, an east/northeastward-ejecting high-level jet analyzed over northern Mexico this morning will reach the southern High Plains by around peak heating/early evening, leading to a further strengthening of mid/high-level westerlies that are already seasonally strong (12Z Midland TX observed sounding). Related to convection overnight/early this morning across the Low Rolling Plains and north-central Texas, an outflow boundary continues to settle/decelerate south into the Permian Basin/Concho Valley including Midland/San Angelo areas, east-southeastward toward the Texas Hill Country. Considerable convective overturning and stabilization has occurred in association with this convection/outflow across the Low Rolling Plains and western North Texas, although steady modification/northward mixing of the boundary should occur especially across the Permian Basin and West Texas South Plains later today. It is in relative proximity to this boundary and the north/south-oriented dry line that will have the highest probability of intense surface-based storm development later today. Intense heating/ample convergence will likely lead to such development by late afternoon. These storms will move into an environment of very high instability (MLCAPE over 3000 J/kg), steep mid level lapse rates exceeding 8.0 C/km, and effective shear values of 40-50 kt. Intense supercells capable of very large hail (some hailstones in excess of 3" in diameter are viable) are expected, particularly within the Moderate Risk area across west/southwest Texas. Although low-level winds are not forecast to be overly strong, the residual influence of the outflow boundary and robust instability will support the possibility of a few tornadoes. Over time, storms should eventually cluster/organize this evening toward the Low Rolling Plains/Big Country with damaging wind potential also increasing as storms progress east-southeastward. ...

Southeast Colorado/south-central High Plains... A moist post-frontal environment in conjunction with low-level upslope flow will be conducive for at least isolated severe thunderstorms by mid/late afternoon initially across southeast Colorado/northeast New Mexico including the Raton Mesa vicinity. Although deep-layer shear will not strong, organized multicells and some transient supercells can be expected with large hail and possibly some tornado risk. These storms should move into additional parts of the region including the Texas/Oklahoma Panhandles and southwest Kansas by early evening with mostly a hail/wind risk continuing. ...

Southeast Texas/western Louisiana... A loosely organized cluster of storms persist across southeast Texas into western/southern Louisiana late this morning. While deep-layer shear and buoyancy are not overly strong, the moist environment and relatively strong low-level shear/SRH have been supportive of transient supercell circulations. This risk may continue this afternoon with at least some potential for a brief tornado and/or locally damaging wind gust, particularly in areas closer to the immediate coast. Read more LIVE: spc.noaa.gov
http://dlvr.it/RzryQ0


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