Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Aug 26 2024 05:59:58 ACUS01 KWNS 260559 SWODY1 SPC AC 260558 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1258 AM CDT Mon Aug 26 2024 Valid 261200Z - 271200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR CENTRAL AND SOUTHERN SOUTH DAKOTA...CENTRAL AND SOUTHERN MINNESOTA...AND WESTERN WISCONSIN... ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF THE CENTRAL HIGH PLAINS TOWARD THE UPPER MISSISSIPPI VALLEY...AND OVER PORTIONS OF SOUTHERN NEW ENGLAND... ....SUMMARY... Severe storms are expected to evolve within a zone extending from the northern/central High Plains eastward to Wisconsin this afternoon into tonight. Large to very large hail, a few tornadoes, and swaths of severe, potentially damaging, gusts are expected, especially across South Dakota into Minnesota. A few severe storms producing strong gusts and hail are also expected across southern New England. ....Synopsis... A pronounced mid-level trough will eject into the Plains and approach the Upper MS Valley while pivoting around a broader anticyclone aloft today. Meanwhile, another mid-level trough over New England will gradually eject into the Atlantic through the day. Several rounds of scattered to potentially widespread thunderstorm development are likely ahead of the upper trough over the Plains/Upper MS Valley this afternoon and evening. Given adequate wind shear and strong to extreme buoyancy preceding the storms, several strong to severe thunderstorms are expected, with all severe hazards likely, especially over SD into central and southern MN. Strong mid-level flow and corresponding modest buoyancy pivoting around the upper trough in the Northeast will foster some severe potential as well. ....Northern Plains into the Upper MS Valley... Multiple rounds of severe thunderstorms are expected across the northern Plains into the Upper MS Valley this afternoon into tonight. Semi-discrete supercells are likely to develop north of a surface low centered along the SD/IA border, along a west-to-east oriented baroclinic zone. Along this boundary, surface dewpoints in the upper 70s F, overspread by 8-9 C/km mid-level lapse rates, will contribute to extreme buoyancy (i.e. MLCAPE reaching at least 4000-5000 J/kg), especially over eastern SD toward the MN/IA border. Coinciding with this extreme buoyancy are modestly curved and elongated hodographs, with at least 35-45 kts of effective bulk shear. As such, initial supercell structures will be capable of all severe hazards, including hurricane-force gusts in forward-flank and rear-flank downdraft regions, and 2+ inch diameter hail. As storm cold pools merge, a bow echo MCS is likely across eastern SD that will track into central/southern MN into the Upper MS Valley. This bow echo is expected to produce a corridor of severe gusts, some of which may exceed 75 mph. A few tornadoes also cannot be ruled out, either with initial semi-discrete supercells, or with line-end or leading-line mesovortices embedded in the bow echo. Rapidly merging thunderstorm clusters across western into central SD are poised to track near where the initial supercells/bow echo should occur. By the time these storms reach this zone, they should have already grown upscale into an MCS (perhaps even a bow echo) accompanied by severe gusts (and a 75+ mph gust cannot be ruled out with these storms as well). A Category 3/Enhanced risk has been expanded over much of central SD to western WI to account for multiple, organized severe wind swaths. ....Central and Northern High Plains... Orographic lift and strong deep-layer ascent immediately preceding the ejecting mid-level trough will support convective initiation over the central and northern High Plains. Scattered to potentially widespread thunderstorms will rapidly progress toward the northern Plains (behind earlier rounds of storms), amid a dry and deep boundary layer characterized by steep low-level lapse rates, and overspread by 30-40 kts of effective bulk shear. Several multicells and supercells are expected by mid to late afternoon, with severe gusts and perhaps large hail accompanying the stronger storms. Clusters of storms may move eastward from WY and northeastward from eastern CO/western KS, possibly merging in the process. Should this occur, then one or more MCSs may develop, possibly accompanied by more focused corridors of severe-gust potential, especially over western into central SD by evening. ....Portions of New England into the Mid Atlantic... A 500 mb impulse/speed max will pivot around the backside of the mid-level trough and overspread portions of the Hudson Valley today, encouraging convective initiation in two zones. First, scattered multicells and perhaps transient supercells should initiate over New England and track southeast toward Cape Cod and Long Island through the afternoon. The stronger mid-level flow will contribute to straight/elongated hodographs and accompanying 30-40 kts of effective bulk (speed) shear. Strong gusts and large hail will accompany the stronger storms. The best chance for any severe wind/hail will be over southern New England, where over 1000 J/kg MLCAPE may overlap the stronger vertical shear to support stronger, longer-lived updrafts. Secondly, a cluster of multicellular/supercellular storms may develop ahead of the 500 mb speed max over the central Appalachians and track southeast toward the Atlantic Coast. Given modest low-level lapse rates and hodograph elongation, strong wind gusts may accompany these storms as well. ...Squitieri/Darrow.. 08/26/2024 $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .