Subj : DAY2SVR: Nws Storm Prediction Center Norman Ok To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jul 20 2023 17:32:12 ACUS02 KWNS 201732 SWODY2 SPC AC 201730 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1230 PM CDT Thu Jul 20 2023 Valid 211200Z - 221200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE LOWER MISSISSIPPI VALLEY INTO THE SOUTHEAST... ....SUMMARY... Strong to severe severe thunderstorms appear possible over parts of the Southeast, Mid-Atlantic into New England, southern/central High Plains, and Southwest on Friday. The greatest potential for scattered damaging winds should exist from parts of the lower Mississippi Valley into the Southeast. ....Synopsis... Upper ridging will persist Friday over much of the Southwest into the northern Rockies. Downstream, an upper trough should move slowly northeastward across the Mid-Atlantic and New England through the period. Between these two features, a broad zone of modestly enhanced mid-level west-northwesterly flow will remain over much of the Plains and eastern states. At the surface, a weak low over northern NY/southern Ontario should develop slowly northeastward through the day in tandem with the upper trough. Attendant cold front extending southward from the surface low across the East Coast states should bend westward across the Southeast into the lower MS Valley. Rich low-level moisture, and appreciable severe potential, should remain confined along/south of this front Friday. ....Lower Mississippi Valley into the Southeast... Thunderstorms posing some threat for strong/gusty winds should be ongoing Friday morning across parts of eastern OK into western AR. This activity will likely be tied to a convectively enhanced mid-level shortwave trough forecast to advance quickly east-southeastward across the lower MS Valley and Southeast through the day. It remains unclear whether this small bowing cluster will persist or slowly weaken through Friday morning as it approaches the Mid-South/lower MS Valley. If it can be maintained and eventually restrengthen as it progresses east-southeastward, then a corridor of greater damaging wind potential is evident from near Memphis TN to the Atlantic Coast, along/south of the weak front and outflow from prior convection. Moderate instability should develop through Friday afternoon across this area with robust diurnal heating of a moist low-level airmass. Modestly enhanced mid-level flow and around 25-40 kt of deep-layer shear will promote convective organization, with the internal dynamics of the MCS or remnant MCV also providing some enhancement to the low/mid-level winds. There also appears to be some potential for additional robust thunderstorm development along the outflow of the morning activity. Regardless of which scenario plays out, enough model guidance suggests potential for scattered strong to severe thunderstorms capable of producing mainly damaging winds to justify adding a Slight Risk. Some threat for hail may also exist with the more robust updrafts. ....Mid-Atlantic into New England... Showers and isolated thunderstorms will probably be ongoing at the start of the period across parts of the Mid-Atlantic into NY, related to convection from today that is forecast develop over the Great Lakes/OH Valley. In the wake of this morning activity, most guidance shows at least modest destabilization occurring ahead of a weak front that should advance slowly eastward through the day. Additional thunderstorms should develop by Friday afternoon along and ahead of this front in a weakly to moderately unstable environment. Even though mid-level winds do not appear overly strong, enough flow and related effective bulk shear should be present for modest updraft organization. Isolated damaging winds and hail may occur with the strongest convection. Based on latest guidance, the Marginal Risk has been expanded northward to include more of the Mid-Atlantic and parts of New England. ....Southern/Central High Plains... Model guidance indicates strong heating and orographic ascent will favor isolated to scattered thunderstorms developing Friday from eastern WY southward to the Raton Mesa vicinity in northeastern NM. Isolated convection may also develop across western NE along/south of a weak surface boundary. It appears a relative minimum in overall thunderstorm coverage may exist south of the Palmer Divide in CO to near the CO/NM border. Still, steep low/mid-level lapse rates and strengthening mid/high-level northwesterly flow with height across the southern/central High Plains should act to organize a few of the stronger updrafts. Isolated large hail and severe gusts should be the primary risks. This activity will likely weaken during the evening as it moves further south-southeastward into the High Plains. .... Southeastern Arizona... Isolated to perhaps widely scattered thunderstorms should develop over the higher terrain of southeastern AZ and vicinity by late Friday afternoon. Large surface temperature-dewpoint spreads are forecast, and this activity will likely remain high-based. Even though deep-layer shear should remain modest, some of this convection could produce isolated severe/damaging winds given the dry sub-cloud layer potential for evaporatively cooled downdraft accelerations. ...Gleason.. 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) .