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Thursday, August 19, 2021

SPC Aug 19, 2021 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1241 AM CDT Thu Aug 19 2021 Valid 191200Z - 201200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE CENTRAL AND NORTHERN HIGH PLAINS... ...SUMMARY... Scattered severe thunderstorms are expected across portions of the central and northern High Plains later this afternoon and tonight. ...Central/Northern High Plains... Water-vapor imagery depicts a well-defined upper trough over the interior northwest/Great Basin region. This feature is forecast to gradually shift east through the day1 period as 50+kt 500mb flow translates through the base of the trough over southern UT, then spreads downstream across northern CO during the evening. Associated mid-level height falls will develop across the High Plains late, which should aid strengthening LLJ across western KS into south-central SD. Boundary layer is seasonally moist across the High Plains at 05z with lower 60s surface dew points observed from eastern CO into the NE Panhandle. Higher moisture content should advect a bit farther northwest over the next 12-18hr before significant afternoon convection develops ahead of the aforementioned trough. A substantial amount of convection is expected to persist through sunrise across eastern UT/western CO into WY with some intensification possible ahead of the front where boundary-layer heating is expected. However, it appears boundary-layer destabilization will be maximized by 21z and CINH will be removed across northeast CO into the NE Panhandle. Forecast sounding at SNY from the NAM exhibits around 3000 J/kg MLCAPE with roughly 1km southeasterly low-level flow and veering through a deep layer. This profile favors supercells and latest thinking is discrete storms should be common, especially early in the convective cycle. Have introduced 5% tornado probabilities across this region to account for potentially tornadic supercells into the evening. In addition, large hail and severe wind gusts appear possible with storms that form ahead of the sagging cold front. ...Southern New England... Remnants of tropical cyclone Fred have spread into the northern Middle Atlantic region early this morning. A well-organized band of convection continues ahead of the weak circulation and currently arcs from the lower Hudson Valley into extreme southeast PA. This activity should propagate into western portions of southern New England early in the period before translating off the Atlantic Coast by early afternoon. It's not clear appreciable heating will be noted in the wake of this early-day activity, and veering low-level flow with poor lapse rates do not favor organized severe later in the day. The primary threat for a brief tornado appears to be with convection prior to about 20z. ..Darrow/Lyons.. 08/19/2021 Read more LIVE: spc.noaa.gov
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