Subj : DAY1 Enhanced Risk Plains To : All From : Dumas Walker Date : Thu Jun 27 2024 08:03 am ACUS01 KWNS 271257 SWODY1 SPC AC 271256 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0756 AM CDT Thu Jun 27 2024 Valid 271300Z - 281200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF THE CENTRAL AND NORTHERN HIGH PLAINS... ....SUMMARY... The greatest severe-thunderstorm threat is over parts of the northern/central High Plains this afternoon and evening. Gusts near 80 mph, damaging hail greater than 2.5 inches and a few tornadoes are possible. ....Synopsis... The mid/upper-level pattern will feature a progressive northern stream, with troughs initially located over the inland Pacific Northwest and over the Northeast. A series of phased vorticity maxima extend from the Northeastern trough southwestward across the central/southern Appalachians to parts of MS/LA in recent moisture- channel imagery. This feature should shift eastward to the eastern Carolinas, southern GA and coastal MS by 00Z, becoming stationary tonight across GA and the Gulf Coast east of LA, but moving offshore from NC and SC. The Northwestern trough will move eastward astride the international border, with a closed 500-mb low forming and moving over extreme southern parts of AB/SK tonight. By 12Z tomorrow, the trough should extend from the southern SK low across central MT to southern ID. Though the flow will remain nearly zonal well to its southeast over the central High Plains, height falls are expected to extend as far south as parts of the OK/TX Panhandles. At the surface, the 11Z analysis showed a cold front across western MT, central ID and northern CA, and a warm front from near HVR across east-central MT, western/southern SD and northern NE. Cyclogenesis will continue over MT through the day, shifting eastward. By 00Z, the main low should reach the MT/ND border area roughly between GDV-DIK, with cold front southwestward across northwestern WY, southeastern ID and central NV. A dryline should sharpen over the High Plains through the day, and by 00Z, extend from near the MT/SD line across eastern CO to the western TX Panhandle. The warm front should extend from the low southeastward over the western Dakotas and central parts of NE/KS, becoming diffuse and fragmented farther southeast. A lingering segment of a separate front should be quasistationary and act as a surface trough/convergence zone across southern parts of AL/GA and the central/eastern Carolinas. ....Great Plains... Scattered thunderstorms are expected to develop in multiple episodes over the northern/central Plains, probably leading off with cold-frontal initiation from late morning through afternoon across parts of western/central MT, where large-scale lift will be strongest with the approach of the northwestern trough aloft. This activity -- which may arise from the same vertical-motion field now associated with convection in higher elevations of southwestern MT -- should move generally eastward over the Plains, with upscale organization possible. Severe gusts (some exceeding 70 mph) and sporadic hail (some exceeding 2 inches diameter) will be the main concerns. Subsequent development is expected closer to the surface low, dryline and warm front over the northeastern MT/western Dakotas area this afternoon/evening, also posing a threat for large to very large hail and severe gusts. Tornado potential will be relatively maximized with any discrete or embedded supercell(s) moving into the plume of greatest low-level moisture and backing of surface flow near the low and warm front (east of the dryline). Deep-layer shear should strengthen throughout the day ahead of the cold front, across the central/northern High Plains, while heating gradually weakens MLCINH, and regional lift increases in relation to low-level cyclogenesis. This will combine with a plume of favorable low-level moisture (dewpoints generally in the 60s F by mid/late afternoon) to support a corridor of MLCAPE in the 1000-2000 J/kg range near and just west of the warm front. Effective-shear magnitudes in the 40-55-kt range (strongest on the northern areas) will support supercell potential, with longer hodographs west of the warm front favoring destructive-hail production. One or more storm clusters may evolve and grow upscale into MCS activity this evening, further reinforcing the wind potential, with support from moisture transport and enhanced storm-relative flow of a 40-50-kt LLJ. Convection should be more isolated southward down the dryline and lee trough into the western KS/OK Panhandle region, with deep shear also weakening southward. However, intense surface heating and somewhat high LCL will foster boundary-layer conditions suitable for at least isolated severe gusts and hail. Some clustering and mesobeta-scale cold-pool aggregation may occur to maximize severe-wind potential for a few hours sub-regionally. ....UT and western parts of CO/WY... Widely scattered to scattered thunderstorms are expected to form atop a seasonally moist, well-heated and weakly capped boundary layer this afternoon, offering locally severe gusts, isolated large hail, and a marginal/conditional tornado threat. This activity should develop as height falls spread over the area related to the Northwestern trough, along/ahead of the surface cold front. Diurnal heating will reduce MLCINH substantially, especially in the presence of moisture characterized by 50s F surface dewpoints remaining in many basins/valleys through the heating mixing cycle, while orographic forcing also aids lift locally. That moisture, combined with steep low/middle-level lapse rates, will support MLCAPE of 500-1500 J/kg, atop favorable subcloud thermal profiles to support downdraft accelerations to severe levels. Although environmental flow should be nearly unidirectional through most of the troposphere, terrain-forced backing will enhanced deep shear locally, with effective-shear magnitudes generally in the 25-40-kt range. Mostly multicells and a few supercells are possible. ....Southeast... Widely scattered to scattered thunderstorms should develop this afternoon into early evening, from the NC Coastal Plain southwestward to southern portions of AL/GA. Damaging to isolated severe gusts will be the main concern. Activity should develop most densely near the remnant front/convergence zone as the mid/upper trough closely approaches, as well as along sea-breeze, outflow and differential-heating boundaries south/southeast of the front. Despite weak midlevel lapse rates, a combination of strong diurnal heating and rich low-level moisture (with surface dewpoints commonly in the upper 60s to mid 70s F) should yield MLCAPE in the 1500-2000 J/kg range. Weak low/middle-level flow will limit vertical shear substantially, and convection should be multicellular in nature with some clustering and local cold-pool development possible. Though moist-, subcloud layers nonetheless should be well-mixed, supporting strong/locally severe downdrafts. ...Edwards/Bunting.. 06/27/2024 $$ --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (21:1/175) .