SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0739 AM CDT Fri May 21 2021 Valid 211300Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS NORTHEAST CO AND THE NE PANHANDLE... ...SUMMARY... A few 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... Late afternoon thunderstorm development appears most probable over northeast CO into the NE 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 should contribute to moderate MLCAPE of 1000-1500 J/kg along the western periphery of 50s 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 yield a few discrete supercells capable of significant severe hail and a couple tornadoes. Convection should tend to consolidate into a cluster during the evening, but may largely propagate towards the cold side of the sharp baroclinic zone. This renders lower confidence in sustaining greater severe coverage farther north across the Dakotas. ...Southern High Plains... 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. ...Upper MS 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 MO Valley 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 LA and southeast TX... 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. ..Grams/Mosier.. 05/21/2021 Read more LIVE: spc.noaa.gov
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