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Wednesday, August 18, 2021

SPC Aug 18, 2021 1730 UTC Day 2 Convective Outlook

SPC 1730Z Day 2 Outlook Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1205 PM CDT Wed Aug 18 2021 Valid 191200Z - 201200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHEAST CO...SOUTHEAST WY...WESTERN NE AND SOUTHWEST SD... ...SUMMARY... A few strong/severe storms may occur from the central and northern High Plains region into the Dakotas Thursday afternoon and evening. ...Central Rockies to Northern Plains... An upper low/trough over the Great Basin/Intermountain West region will slowly migrate eastward toward the Rocky Mountains and adjacent High Plains on Thursday/Thursday night. An associated belt of enhanced southwesterly deep layer flow ahead of the trough will overspread much of CO into eastern WY and the central/northern High Plains. At the surface, a cold front will extend from the central Dakotas into eastern CO Thursday morning. The front will not progress much until later in the period when stronger height falls overspread the region and a deepening lee low develops over eastern CO during the late afternoon/evening. As this occurs, strong low level warm advection will maintain 60s F dewpoints ahead of the front (lower further west across higher terrain in CO/WY) and a south/southwesterly low level jet will increase during the evening across the central/northern High Plains vicinity. Thunderstorms are expected to develop over the higher terrain of western/central CO into WY by late morning/early afternoon closer to stronger ascent near the upper low. Steepening low level lapse rates and moderate vertical shear will support storms capable of hail and strong gusts. Stronger heating and higher dewpoints further east over the High Plains will aid in additional thunderstorm development and/or maintain activity moving off higher terrain during the late afternoon. Initial more discrete cells will be capable of large hail and damaging gusts. Toward evening, the increasing low level jet may support organized clusters growing upscale into one or more bowing segments, increasing potential for damaging gusts. ...Southern New England... Showers and thunderstorms associated with the remnant low from former Tropical Depression Fred will be ongoing Thursday morning across parts of southern New England. A tropical airmass will be in place over the region with favorable low level shear for storm rotation. Instability is expected to remain weak across the region, but given a deep, moist boundary layer and effective SRH values around 125-200 m2/s2, a couple of brief spin-ups could occur along the eastern periphery of the low as the system tracks north/northeast through the afternoon. ..Leitman.. 08/18/2021 Read more LIVE: spc.noaa.gov
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