Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jul 24 2023 12:58:43 ACUS01 KWNS 241258 SWODY1 SPC AC 241257 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0757 AM CDT Mon Jul 24 2023 Valid 241300Z - 251200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS MORNING OVER PARTS OF WESTERN/CENTRAL MISSOURI AND EXTREME EASTERN KANSAS... ....SUMMARY... Thunderstorms associated with strong wind gusts and hail will be possible today across parts of the lower Missouri Valley, mid to upper Mississippi Valley, Ohio Valley and Northeast. ....Synopsis... The fundamental mid/upper-level pattern will change little through the period, featuring a mean trough in the East, and a strong anticyclone centered on a roughly 600-decameter 500-mb high near FRM. Ridging will persist north of the high to the western Canadian prairies, with slight eastward shift as a strong synoptic-scale cyclone moves inland over southwestern/central BC. A series of subtle perturbations will traverse the cyclonic flow around the eastern trough, some (such as a possible MCV evolving from convection now over the lower Missouri Valley) being convectively augmented/generated. At the surface, 11Z analysis showed a wavy, quasistationary frontal zone from a low over coastal NC northeastward across the Atlantic, and southwestward over southern GA. Another nearly stationary to war front was drawn from southeastern MT across central NE to northwestern and central MO. This front is being modulated over the MO Valley by outflow from an MCS that developed atop the elevated slope of this front. ....Lower Missouri Valley region to Ohio Valley... An MCS with a history of severe gusts and large hail is moving southeastward through the northwestern MO/northeastern KS region, and may continue to pose a severe threat for a few more hours. See Severe Thunderstorm Watch 543, and related mesoscale discussions, for the latest near-term guidance on this activity. Scattered thunderstorms in clusters are expected to develop amid the mid/upper-level cyclonic flow, from the mid Mississippi Valley region over the lower Ohio Valley. Activity also may develop ahead of the MCV from the morning activity. Convection should be predominantly diurnal, with greatest coverage this afternoon in the form of multicellular clusters offering at least isolated damaging to severe gusts, and isolated large hail. A corridor of 2000-3500 J/kg MLCAPE, supported by surface dewpoints commonly in the upper 60s to low 70s F, should develop by midafternoon, atop steep lapse rates in the subcloud mixed layer (for gust support). However, only around 25-30 kt effective-shear magnitudes are expected over most of the area. Boundaries from morning clouds/convection, once settled into position for the strongest daytime heating and minimal MLCINH, may focus convection. More-concentrated, mesobeta-scale severe potential may develop within this broad swath; but for now, too much uncertainty remains to assign greater unconditional probabilities, aside from the short-term projected path of the ongoing Missouri Valley MCS. ....Northeastern CONUS... Widely scattered to scattered multicellular thunderstorms are expected to develop from midday through afternoon over a broad swath of the Northeast, from the eastern lake-breeze regime of Lake Erie across NY to western New England, and southwestward toward the northern VA Blue Ridge region. The environment will be supported aloft by weak large-scale ascent preceding the mid/upper-level trough, Despite being north of the front, favorable moisture is expected (surface dewpoints mainly 60s F) to combine with diurnal heating to weaken CINH. Broad low-level convergence is forecast across the region, aiding in potential thunderstorm coverage. While vertical shear should remain modest, favorable boundary-layer lapse rates will exist to support potential for damaging to isolated, marginally severe gusts. ....Upper Mississippi Valley... Diurnal heating, residual boundary-layer moisture northeast of the warm front, and weak large-scale lift preceding a northwest-flow perturbation aloft, each should contribute to potential for widely scattered thunderstorms this afternoon. Deep-layer shear will be favorable across this region, given strong veering of winds with height from the surface through mid/upper levels, and strong upper/anvil-level flow. However, modest midlevel lapse rates and lack of more substantial moisture should keep MLCAPE below about 800 J/kg over most of the area. A well-mixed subcloud/boundary layer may support strong/damaging gusts in the most vigorous cells. ....Western CONUS... Isolated to widely scattered, mainly afternoon to early evening thunderstorms are possible over a large area of the West, especially in the monsoonal easterlies of southern AZ, and in southwesterly gradient flow over the northern Rockies/northern UT region, well ahead of the landfalling BC cyclone. While isolated strong-severe gusts cannot be ruled out atop a very deep/well-mixed subcloud layer this afternoon, overall potential looks too nebulous/unfocused to target a specific unconditional area at this time. ...Edwards/Mosier.. 07/24/2023 $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. 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