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Friday, May 21, 2021

SPC May 21, 2021 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1130 AM CDT Fri May 21 2021 Valid 211630Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE CENTRAL HIGH PLAINS... ...SUMMARY... Severe thunderstorms are most likely across northeast Colorado and the Nebraska Panhandle during the late afternoon to early evening. Very large hail and a couple tornadoes are possible. ...Central High Plains to the Dakotas... A weak disturbance coincident with neutral/slightly falling upper heights and strengthening south-southwesterly winds aloft will influence the region into this afternoon and evening. Late afternoon thunderstorm development appears most probable over northeast Colorado into the Nebraska Panhandle in the vicinity of a lee cyclone and slow-moving cold front. Robust boundary-layer heating near the dryline with surface temperatures warming through the 80s F should contribute to moderate MLCAPE of 1000-1500 J/kg along the western edge of 50s F surface dew points. Very steep mid-level lapse rates (8-9 C/km) and strengthening mid-level south-southwesterlies with the impinging of a speed max from the Four Corners should contribute to some isolated semi-discrete supercells capable of significant severe hail and possibly a couple tornadoes. Convection should tend to consolidate into a cluster during the evening with some increased wind potential, although convection may largely propagate towards the cold side of the sharp baroclinic zone. ...Southern High Plains... Isolated high-based convection should develop along the lee trough by late afternoon. Isolated severe wind gusts will be the primary hazard, given the very warm and deeply mixed boundary layer and moderate southerly low to mid-level flow. This threat will be diurnally driven and should eventually diminish with time this evening, although a secondary round of isolated thunderstorms could occur late tonight/early Saturday mainly across northeast New Mexico as additional forcing for ascent glances the region. ...Southern Idaho/western Wyoming... The exit portion of a strong polar jet will influence the region in advance of the upper trough centered over the Great Basin. Forcing for ascent coupled with adequate moisture and steep lapse rates will contribute to an afternoon-maximized potential for isolated/widely scattered low-topped thunderstorms. Some hail and gusty winds may occur on a localized basis. ...Upper Mississippi Valley/Great Lakes... A regime characterized by deep moisture and modestly enhanced low to mid-level flow will persist within a broad warm conveyor from the central Gulf Coast to the Upper Great Lakes. An MCV near the Lower Missouri Valley/eastern Iowa should move northeast with pockets of weak destabilization possible ahead of it. Weak mid-level lapse rates will be a limiting factor and convection may largely remain in the form of low-topped showers. But a few updrafts might sufficiently deepen for transient low-level rotation capable of producing a brief weak tornado. ...Southwest Louisiana/southeast Texas... Low-level hodographs should slowly shrink in size as winds subside through the day. However, an increase in low-topped showers and thunderstorms is expected into this afternoon in association with an MCV drifting northwest from the northwest Gulf. Temporal overlap should exist for the potential of a few updrafts with transient low-level rotation capable of producing a brief weak tornado. ..Guyer/Kerr.. 05/21/2021 Read more LIVE: spc.noaa.gov