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Monday, May 24, 2021

SPC May 24, 2021 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0257 PM CDT Mon May 24 2021 Valid 242000Z - 251200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHERN HIGH PLAINS AND CENTRAL PLAINS... ...SUMMARY... Scattered severe thunderstorms are possible, late this afternoon through this evening, over parts of the central Plains into the southern High Plains. Other strong to severe storms are possible across the Mid-Atlantic States and upper Mississippi Valley. ...DISCUSSION... A couple of changes have been made to the outlook for this issuance. The first change is to remove the slight risk from parts of northeast Nebraska. Convection is not expected to develop in northeast Nebraska until after dark when instability will be less favorable for a severe threat. The slight risk is focused across south-central and east-central Nebraska where the combination of instability and deep-layer shear is forecast to be more favorable for supercells. The second change is to adjust the marginal risk area eastward across southeast Nebraska and west-central Iowa, to account for a chance of isolated severe convection in the overnight hours. ..Broyles.. 05/24/2021 .PREV DISCUSSION... /ISSUED 1129 AM CDT Mon May 24 2021/ ...Central Plains to southern Minnesota/northern Iowa... A southwest/northeast-oriented front has generally stalled across the region, with low/some middle 60s F surface dewpoints near and southeast of this front. A northeastward-moving shortwave trough/speed max will at least glancingly influence the frontal zone by around peak heating. Front aside, a lingering outflow boundary/zone of differential heating to the northeast of a southeast Colorado surface low and near/southeast of the synoptic front may be a particular focus for intense storm development later this afternoon across western Kansas. Sufficient deep-layer shear will exist in vicinity of the front/outflow to support a mixed mode of multicell clusters and supercells as storms develop during the mid to late afternoon. Large hail/damaging winds will be possible, and some tornado potential will also exist, particularly in vicinity of the western Kansas boundary late this afternoon/early evening. As the low-level jet increases this evening, modest upscale-type storm organization may occur across western toward west-central/north-central Kansas, while additional late-night development is also plausible from far eastern Colorado into northern Kansas/far southern Nebraska, with at least some continued potential for locally severe hail/wind. ...Southern High Plains... Scattered thunderstorms will likely develop across the higher terrain of the Texas Trans-Pecos and along the front/dryline from southeast New Mexico into the western Oklahoma/Texas Panhandles late this afternoon. Semi-steep mid-level lapse rates atop the western periphery of upper 50s/low 60s F surface dewpoints will support upwards of 1500-2500 J/kg MLCAPE by peak heating. Low/mid-tropospheric winds will be relatively weak (20 kt or less) but ample instability will support some intense multicells, including the possibility of upscale quasi-linear growth through early/mid evening across the west/northwest Texas Plains and southern Texas Panhandle. A combination of large hail and severe-caliber winds can be expected. ...Central Virginia/eastern West Virginia to North Carolina... A west/southwestward-moving backdoor cold front will influence the region with a moist (60s F surface dewpoints) and moderately unstable environment along and west/south of the front this afternoon. Influenced by a subtle southeastward-moving mid-level disturbance, initial thunderstorm development/intensification is most probable this afternoon along the West Virginia/Virginia border region and Blue Ridge vicinity, with storms subsequently spreading generally southward into other parts of southern Virginia and northern North Carolina through late afternoon and early evening. As much as 30 kt of effective shear, maximized in the immediate vicinity of the front, and a warm/well-mixed boundary layer will support the possibility of isolated damaging wind gusts. ...Northern Wisconsin... The region will be influenced by steady height falls and strengthening southwesterly winds aloft in advance of the upper trough centered over the Canadian Prairies and northern High Plains/Dakotas. A warm front will continue to spread northward across the northern half of Wisconsin toward the Upper Peninsula of Michigan. A regional maximization of modest destabilization and somewhat stronger deep-layer/low-level shear should occur across northwest Wisconsin in vicinity of the warm front, where some transient supercells will be possible late this afternoon and early evening. Read more LIVE: spc.noaa.gov
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