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Tuesday, May 25, 2021

SPC May 25, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0256 PM CDT Tue May 25 2021 Valid 252000Z - 261200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHERN AND CENTRAL PLAINS AND IN THE UPPER MISSISSIPPI VALLEY... ...SUMMARY... Scattered severe thunderstorms with large hail and damaging winds are possible in parts of the upper Mississippi Valley, western Great Lakes, southern High Plains and central Plains. ...DISCUSSION... The main change to the outlook for this issuance is to remove the slight risk area from the Arrowhead of Minnesota and from Lake Superior. The airmass is stable over Lake Superior. Cells that move over the water could still obtain a marginal wind damage and hail threat although an organized severe threat is not expected. Also, the western edge of the marginal risk area has been moved a bit eastward across far eastern Minnesota. ..Broyles.. 05/25/2021 .PREV DISCUSSION... /ISSUED 1146 AM CDT Tue May 25 2021/ ...Central/Southern Plains... Late afternoon to evening thunderstorm development is still anticipated with isolated to widely scattered coverage along the dryline from the Texas Trans-Pecos north towards the composite front/outflow intersection in the Texas South Plains/Panhandles into south-central Kansas. Although mid-level westerlies will remain weak under the influence of modestly building upper heights, moderate to strong destabilization is expected this afternoon with ample MLCAPE generally on the order of 2000-3000 J/kg. While deep-layer shear will be modest, a few organized multicell clusters with embedded supercell structures should prove favorable for isolated to potentially scattered large hail and severe wind through this evening, with the likely evolution of multiple southeastward-moving clusters this evening. Given the degree of buoyancy and steepness of lapse rates across the Permian Basin to Concho Valley, and the influence of the modifying outflow across the West Texas South Plains towards the Edwards Plateau, significant severe appears most possible in these regions. ...Upper Great Lakes... A shortwave trough over southern Manitoba/northern North Dakota will modestly amplify as it continues east-southeastward along the International Border toward the Lake Superior vicinity by tonight. Primary surface cyclogenesis will occur over northern Ontario, while a cold front progresses eastward and reaches a northwest Wisconsin/southeast Minnesota to northwest Iowa corridor by around peak heating. Although plentiful cloud cover persists across the warm sector at late morning, gradual clearing will occur with ample heating and 60s F surface dewpoints likely yielding 1000-2000 J/kg MLCAPE by mid/late afternoon. It appears adequate low-level convergence will be present for isolated/widely scattered thunderstorm development initiating across the Minnesota Arrowhead and western Wisconsin and possibly southeast Minnesota by around 20-22Z. Relatively long hodographs (40-55 kt effective shear) related to nearly unidirectional southwesterly winds will support some initial supercells capable of severe hail and possibly some tornado risk. Strengthening flow in the mid-levels should otherwise support the possibility of upscale growth into organized clusters with embedded mid-level updraft rotation. Overall convective intensity should wane into late evening/overnight as storms approach the Lake Michigan vicinity. ...Northeast Texas/ArkLaTex... Related to persistent/generally weakening convection, multiple weak MCVs appear to exist across north-central Texas and eastern Oklahoma. Preceding these MCVs and a linear cluster of storms across north Texas (near the DFW Metroplex at late morning), the air mass is moist (upper 60s to lower 70s F surface dewpoints) and will likely become moderately unstable this afternoon. A renewed intensification of storms seems probable this afternoon as the boundary layer destabilizes. Some of these stronger storms will be capable of isolated wind damage, while the moist environment and residually strong MCV-related low-level winds could support a brief tornado risk. ...West New York/Northwest Pennsylvania... Strong heating is expected across western portions of New York/Pennsylvania which will allow surface temperatures to warm towards the low 80s in the lee of Lake Erie. Although deep-layer flow will not be that strong, steep low-level lapse rates and MLCAPE around 500 J/kg could support a couple robust cells capable of producing locally damaging winds. ...Southeast Oregon/southern Idaho... Forcing for ascent related to an eastward-moving shortwave trough coupled with a semi-moist environment and differential heating will contribute to increasing thunderstorm potential this afternoon, some of which may be strong to locally severe. Sufficient moisture/buoyancy may exist for hail, particularly across southeast Oregon into southwest Idaho, while a well-mixed boundary layer and strengthening mid-level southwesterly winds may contribute to some strong thunderstorm wind gusts. Read more LIVE: spc.noaa.gov