Severe Storm Outlook Narrative (AC)
Issued by NWS
Issued by NWS
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064 ACUS01 KWNS 031630 SWODY1 SPC AC 031628 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1128 AM CDT Wed Jul 03 2024 Valid 031630Z - 041200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN/CENTRAL PLAINS...AND THE OZARKS INTO PORTIONS OF THE OHIO VALLEY... ...SUMMARY... Scattered severe thunderstorms appear possible this afternoon and evening across parts of the northern/central High Plains, and from the Ozarks into the Ohio Valley. The most favorable corridor for isolated very large hail and significant severe wind gusts is centered on the central High Plains. ...Synopsis... An upper trough will continue moving eastward across Ontario and the Great Lakes today, while an upper high remains centered over the Southeast. Farther west, a separate mid-level shortwave trough will advance east-southeastward from the northern Rockies to the northern/central High Plains through tonight. Multiple convectively augmented mid-level vorticity maxima will move generally east-northeastward across the central Plains into the mid MS and OH Valleys. At the surface, a cold front extends from the OH Valley southwestward to the southern Plains. Weak lee cyclogenesis is forecast to occur across the central High Plains through late this afternoon, and modest low-level moisture return is anticipated to the north of the front and east of a weak surface lee trough across parts of the northern/central Plains. ...Northern/Central Plains... Morning clouds and lingering convection across parts of the central Plains will hamper the development of instability today, especially with eastward extent into NE/KS. Even so, pockets of filtered daytime heating will occur across the northern/central High Plains along and east of the surface lee trough. With steepened mid-level lapse rates present over eastern CO/WY into western SD/NE, a narrow zone of moderate instability is forecast to be in place prior to robust convective initiation this afternoon. Initial development should occur along the length of the lee trough from parts of western NE into eastern CO. A somewhat separate area of convection may also develop from northeastern WY to the Black Hills, as large-scale ascent preceding the mid-level shortwave trough overspreads this region. Modest low-level east-southeasterly flow will quickly veer to westerly at mid/upper levels, with some strengthening and hodograph elongation. Corresponding strong deep-layer shear will support supercells initially, with attendant threat for large hail. Given relatively cool temperatures aloft and the presence of steep mid-level lapse rates, isolated very large hail greater than 2 inches in diameter appears possible. A small zone with favorable overlap of moderate instability, strong deep-layer shear, and sufficient low-level shear remains apparent over parts of the NE Panhandle into northwest NE. This area may have a locally greater threat for a couple of tornadoes with any supercells that can persist late this afternoon into the early evening, assuming the boundary layer does not become too well mixed. Otherwise, upscale growth/clustering appears probable this evening as convective outflows aggregate into the central Plains. Severe/damaging winds should become the main threat as this occurs, with isolated significant gusts up to 75 mph possible if a more consolidated bow/MCS can develop. Confidence in this occurring still remains somewhat low, but the best chance for a more concentrated corridor of severe winds remains across parts of eastern CO into southwest NE and northwest KS this evening. ...Ozarks to the Ohio Valley... A rather moist low-level airmass remains present along/south of the front today, with surface dewpoints generally in the low to mid 70s, and precipitable water values around 1.75-2.2 inches. A fair amount of convective cloud debris is present along/near the front across the mid MS Valley. This will tend to slow diurnal destabilization to some extent across this area. Mid-level lapse rates are also expected to remain poor. Still, moderate to locally strong instability and steepened low-level lapse rates are forecast to develop through peak afternoon heating along/south of the front, which will extend from the Ozarks northeastward into parts of the OH Valley. Low-level winds are expected to remain generally weak, but a modest increase in southwesterly winds at mid levels should foster sufficient deep-layer shear to support some updraft organization. Mainly multicell clusters should develop this afternoon, focused along the front. Some of this activity may produce scattered damaging winds through early evening before eventually weakening. Morning guidance shows a greater concentration of thunderstorms with clustering potential across the Ozarks into the mid MS Valley. ..Gleason/Thornton.. 07/03/2024 $$