Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jul 20 2023 13:02:08 ACUS01 KWNS 201302 SWODY1 SPC AC 201300 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0800 AM CDT Thu Jul 20 2023 Valid 201300Z - 211200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS MIDWEST/GREAT LAKES AND SOUTH-CENTRAL HIGH PLAINS... ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE TENNESSEE VALLEY AND SOUTHEAST... ....SUMMARY... Scattered severe thunderstorms are expected near the Colorado Front Range into the central/southern High Plains, with other severe storms across the Midwest/Great Lakes, as well as the Tennessee Valley and Southeast States. ....Front Range/South-central Plains... A relatively active severe-weather day is expected across the region from mid/late afternoon into tonight. A shortwave trough/speed max over northern Utah/southern Wyoming and northwest Colorado this morning will continue eastward today, and then more southeastward tonight as wave amplification occurs. Surface low development across southeast Colorado will enhance moist low-level upslope flow into the Colorado/northeast New Mexico and southeast Wyoming Front Range today. Scattered thunderstorms are expected to initially develop over the higher terrain/Front Range areas by around mid-afternoon. Moderate to locally strong buoyancy and relatively strong mid/high-level westerlies (40+ kt effective shear) will support initial supercells capable of large hail, with some hailstones greater than 2 inches in diameter. Storms will generally increase in coverage/intensity as they move east-southeastward late this afternoon into evening. With time, a bowing MCS is expected to develop across far eastern Colorado into western Kansas and shift east/southeast into tonight along a strong instability gradient/baroclinic zone oriented near the Oklahoma/Kansas border vicinity. Once clustering and upscale development occurs, a swath of damaging wind (with some gusts greater than 75 mph) could occur, with the greatest potential for significant-caliber wind gusts appearing to be from around 23z through 06z. ....Great Lakes/Ohio Valley/Northeast States... A progressive shortwave trough near Lake Superior early this morning will continue east-southeastward today, with a belt of seasonally strong west-northwesterly winds aloft overspreading the majority of the Midwest/Ohio Valley and Tennessee Valley through this evening. A related surface low will cross Michigan into Ontario, while an east/southeastward-advancing front spreads across the Midwest/Great Lakes toward the Mid-South/Tennessee Valley. A preceding warm front will spread north-northeastward today toward Lower Michigan and the Lake Erie vicinity, allowing for appreciable boundary layer moistening from the southwest by peak heating. Mid 60s to low 70s F dewpoints will reside beneath semi-steep mid-level lapse rates, supporting a corridor of strong destabilization (MLCAPE to 3000 J/kg), especially across parts of Indiana into western/northern Ohio and southern Lower Michigan. Some stronger/potentially severe storms could occur as early as this morning, but the primary scenario is expected to be gradually increasing and intensifying thunderstorm development this afternoon, initially across northern/western Lower Michigan and northern Indiana, with these storms spreading east-southeastward while additional development occurs southwestward near the advancing cold front across Indiana/Ohio. Moderate to locally strong buoyancy coincident with moderately strong westerlies aloft /40+ kt effective shear/ will support some initial supercells capable of large hail, particularly across southern Lower Michigan and northern portions of both Indiana/Ohio. This same corridor is also most likely to see the greatest coverage of storms, particularly with eastern extent, as storms mergers occur and grow upscale by late afternoon/early evening with an increased damaging wind potential. Some tornado risk will exist as well. At least some lingering severe potential should spread east-southeastward through late tonight over the upper Ohio River Valley toward the northern Appalachians including New York/Pennsylvania through the early morning hours of Friday. A relatively moist air mass and relatively weak nocturnal inhibition, as far north as northern Pennsylvania and southern New York, coupled with strengthening deep-layer/low-level winds, could support storms capable of damaging winds/some hail and possibly a tornado risk. ....Tennessee Valley to Georgia/South Carolina... For short-term details, see Mesoscale Discussion 1638. Multiple corridors of severe-weather potential may evolve across the region today into tonight. Initially, a slow-moving but semi-organized storm cluster has evolved overnight and persists across eastern Tennessee/western North Carolina this morning, while more extensive convection exists across a broad part of southern Missouri. These corridors of convection, particularly for areas to the their south/east, and related MCVs will influence downstream convection development and persistence into a diurnally destabilizing boundary layer into the afternoon. Storm organization will be supported by notably strong mid-level west-northwesterly winds aloft for the season, as sampled by the 12z observed sounding from Nashville /40+ kt winds between 3-6km AGL/. Multiple corridors of generally southeastward-moving storm clusters, perhaps materializing as one or more upscale-growing MCSs, should spread across the region today, with some additional strong/severe storms possible late tonight across the Mid-South/Tennessee Valley. ...Guyer/Kerr.. 07/20/2023 $$ = = = 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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .