SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0707 AM CDT Sun May 23 2021 Valid 231300Z - 241200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS WESTERN SD/NE... ...SUMMARY... Scattered to numerous severe thunderstorms are expected across a large portion of the western Great Plains. The most likely corridor for a few tornadoes and significant severe wind/hail is from western South Dakota to the central High Plains. ...Western/central SD to the CO/KS border... A surface cyclone in the lee of the Front Range will deepen as it tracks north-northeast into western SD by this evening. Northward advancement of the low in tandem with the surface warm front will result in poleward advection of upper 50s to lower 60s surface dew points towards the SD/ND border. Moderately steep mid-level lapse rates of 7-7.5 C/km should support an increasingly expansive plume of moderate buoyancy with MLCAPE of 1000-2000 J/kg by peak heating. Pronounced mid-level height falls will overspread the region as a vort max embedded within the basal portion of the broader trough over AZ ejects northeast. Accompanied by an intense speed max, thunderstorms will rapidly develop by early to mid-afternoon within a strengthening deep-layer shear regime. Supercells will be favored initially but a quick transition into a northeast-moving QLCS is expected near the WY/SD/NE/CO border areas given the meridional flow regime. Large hail will be likely mainly early, with severe wind gusts becoming the primary hazard as upscale growth occurs across western portions of SD/NE. The potential for a few tornadoes is apparent across three primary corridors within the ENH and SLGT risk regions. First, any storm in proximity to the surface cyclone and warm front, where locally enhanced 0-1 km SRH (at or above 200 m2/s2) will exist. Second, embedded QLCS circulations are also possible as the line matures during the late afternoon to early evening. Finally to the south of the QLCS, a couple discrete supercells may persist through about dusk near the CO/KS border amid plentiful low-level moisture/SRH. ...Southern High Plains... Isolated to scattered thunderstorms are expected to develop during the afternoon in the vicinity of the dryline from the Raton Mesa vicinity to the Trans-Pecos of far west TX. A mix of supercells and multicell structures will be most favored in the Raton Mesa vicinity along the glancing periphery of the ejecting trough. Large hail, severe wind gusts, and a tornado or two are possible. ...Northeast... Convective coverage will likely remain sparse owing to modest convergence along a predominately west/east-oriented cold front, which will be pushing south across the region this afternoon. Despite weak mid-level lapse rates, surface temperatures warming into the 80s amid upper 50s to low 60s dew points should support weak buoyancy with MLCAPE of 250-750 J/kg. Along the periphery of a mid-level speed max ejecting across northern ME, adequate and nearly unidirectional deep-layer shear will exist for a few cells capable of producing locally damaging winds. ..Grams/Mosier.. 05/23/2021 Read more LIVE: spc.noaa.gov
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