Subj : DAY2SVR: Nws Storm Prediction Center Norman Ok To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jun 18 2023 17:32:21 ACUS02 KWNS 181732 SWODY2 SPC AC 181730 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1230 PM CDT Sun Jun 18 2023 Valid 191200Z - 201200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHEAST... ....SUMMARY... Severe thunderstorms capable of producing mainly damaging winds will be possible across parts of the central Gulf Coast states into Georgia and north Florida on Monday. Additional isolated strong to severe thunderstorms also are possible into eastern Tennessee and parts of the Carolinas, central Texas, and the northern Plains. ....Synopsis... A weak upper trough/low centered over the lower OH Valley should advance slowly eastward on Monday. A belt of 35-50 kt west-northwesterly mid-level flow on the south/southwest flank of the upper low is forecast to persist over much of the lower MS Valley and Southeast. An occluded surface low over the lower OH Valley Monday morning should weaken further through the day as it develops towards the TN Valley and southern Appalachians. A very moist low-level airmass should persist from central/east TX into the lower MS Valley and Southeast. ....ArkLaTex into the Southeast... Latest guidance suggests thunderstorms across the Southeast will probably be in a weakening phase Monday morning. Still, this activity will spread southeast into a destabilizing airmass through late morning and early Monday afternoon. Convection should increase in intensity as the boundary layer becomes moderately to strongly unstable as diurnal heating occurs. Severe/damaging gusts will be the main hazard associated with this activity given its mainly linear/cluster nature and as low-level lapse rates steepen. The Slight Risk has been expanded eastward into more of east/coastal GA and north FL, as most high-resolution models show robust clusters moving across these areas Monday afternoon. Isolated large hail may also occur with the strongest embedded cores. There is still considerable uncertainty regarding the westward extent of severe potential. Some guidance suggests convection may build westward along the weak surface boundary into LA. However, capping also will be stronger to the west, and convection may tend to remain rather isolated. Have opted to expand the Marginal Risk into the ArkLaTex for possible elevated convection late Monday night. As waves of large-scale ascent pivot around the upper low, additional bands of thunderstorms are expected further north and east across eastern TN into the Carolinas. Instability will be weaker with northward extent. However, steepening low-level lapse rates and a high PW environment may support sporadic strong/damaging wind gusts. Additional clusters of strong storms may develop along sea-breeze boundaries across the FL Peninsula. Water-loaded downdrafts may pose a risk for strong gusts here as well, along with occasional hail. ....Central Texas... Upper ridging is expected to remain in place over the southern Plains Monday, with large-scale subsidence generally prevailing. Even so, a dryline is forecast to mix eastward across central TX through late Monday afternoon. Temperatures will likely soar into the 100s via strong daytime heating along the length of the dryline. Most high-resolution guidance continues to show at least isolated thunderstorms initiating along the dryline across central TX by late Monday afternoon. Any convection that can be sustained will have the potential to become a supercell, as northwesterly flow strengthening with height at mid/upper levels will provide 40-50 kt of effective bulk shear. Given the presence of steep mid-level lapse rates and moderate to strong instability, isolated large hail may occur with any supercell. Severe/damaging winds also appear possible, as the boundary layer should be very well mixed, with steepened low-level lapse rates due to the robust diurnal heating. The spatial and temporal extent of the severe threat will likely be constrained by increasing MLCIN with eastward extent and nocturnal cooling of the boundary layer. Given latest trends in high-resolution guidance, have expanded the Marginal Risk a bit. But, confidence in greater coverage of severe thunderstorms remains too low to include higher severe hail/wind probabilities. ....Eastern Montana into North Dakota... A pronounced upper trough/low over the Pacific Northwest and western Canada should undergo some amplification across the western CONUS on Monday. A southwesterly mid-level jet is forecast to overspread parts of the northern High Plains through the period. Low-level moisture should gradually increase through Monday afternoon from eastern MT into ND along/east of a weak front. Large-scale ascent associated with the mid/upper-level jet may encourage isolated thunderstorms to develop across northern WY near the Bighorn Mountains. If it develops, this convection would spread quickly northeastward across eastern MT and into parts of western/central ND through Monday evening. Even though instability should remain fairly weak, deep-layer shear appears strong enough to support supercells with attendant threat for large hail and severe wind gusts. With most high-resolution guidance suggesting 1 or 2 supercells will develop, have added low hail/wind probabilities across this region. ...Gleason.. 06/18/2023 $$ = = = 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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