Subj : DAY2SVR: Nws Storm Prediction Center Norman Ok To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Aug 12 2023 17:19:11 ACUS02 KWNS 121719 SWODY2 SPC AC 121717 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1217 PM CDT Sat Aug 12 2023 Valid 131200Z - 141200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN AND CENTRAL PLAINS TO THE MIDDLE MISSISSIPPI...LOWER OHIO AND TENNESSEE VALLEYS... ....SUMMARY... Severe thunderstorms are possible Sunday from portions of the southern and central Plains into the Middle Mississippi, Lower Ohio and Tennessee Valleys. A mid/upper shortwave trough is forecast to develop south and east across the northern/central Plains on Sunday, becoming oriented from MN/WI to KS/OK by Monday morning. Ahead of this main wave, a lead shortwave impulse and convective enhanced vorticity maxima near the mid/lower MO Valley Sunday morning is expected to shift east across Mid-MS/Lower OH valley vicinity through the afternoon/evening, becoming oriented over VA/NC by Monday morning. At the surface, a moist airmass with dewpoints from the mid 60s to mid 70s F will be in place from the central/southern Plains through much of the Mid-South and Southeastern U.S., with a corridor of 60s F dewpoints expanding into New England. A cold front will be oriented southward from a low over Quebec and extending through western New England during the morning and along the Mid-Atlantic coastal vicinity. The western extent of the front will extend roughly along the Mid/Lower OH Valley to the Mid-MS Valley from northern KY into southern IN/IL and central MO, though this position is more uncertain, and the boundary may lift northward a bit as an effective warm front due to a strong warm advection regime during the day ahead of the main mid/upper shortwave trough. Another surface low is forecast to spread east across SD into MN/IA. A cold front attendant to this low will develop southeast across the central Plains, extending from eastern NE to western KS by 00z. Complicating the forecast scenario for Sunday is convection likely ongoing at the beginning of the period somewhere across the Ozarks vicinity. The location of this convection will depend on the evolution of an expected MCS over KS/OK in the Day 1 (Saturday) period. Outflow from this activity will extend across northern OK to southern MO. These multitudes of surface boundaries will be a focus for severe thunderstorm potential across the Northeast, and from the central/southern Plains to the Mid-MS/Lower OH Valley areas. ....Central/Southern Plains to MS/OH/TN Valleys... Ongoing convection across MO will shift east/southeast through the morning/early afternoon. The evolution of this activity is a bit uncertain. Some guidance shows a weakening trend through the morning, while other solutions maintain some form of clustering or MCS into portions of KY/TN. The downstream airmass will be very moist and strongly unstable while 0-6 km shear increases with time. If this convection persists, or new convection develops along outflow associated with this activity, some severe risk (mainly damaging wind/hail) will be possible into KY/TN and vicinity. The Slight (level 2 of 5) and Marginal (level 1 of 5) have been expanded some to the east/southeast to account for this potential. During the afternoon, convection is expected to develop over the southern High Plains in a moist upslope flow regime. This activity will pose a risk for severe gusts given a deeply mixed boundary-layer to around 700 mb. Clustering of this activity may develop eastward toward residual outflow across northern OK with time. At the same time, the central Plains cold front will develop southeast, triggering convection from the Mid-MO Valley to central KS. As the cold front and outflow merge from northern OK/southern KS into central/southern MO during the evening, convection will increase in a mixed mode scenario with semi-discrete cells and line segments/bows possible. Where semi-discrete convection is maintained, tornado potential will be increased. This appears most likely across parts of central/southern MO near the quasi-triple point/intersecting surface boundaries. The most likely hazard will be damaging gusts given the strongly unstable environment amid seasonally strong vertical shear and an increasing low-level jet during the evening. Sporadic large hail is also possible. There may be a corridor of Enhanced (level 3 of 5) risk potential somewhere from northern OK/southern KS into central/southern MO, but confidence remains too low to upgrade the risk area at this time given uncertainty in morning convection and position of surface boundaries. ....New England... Low to mid-60s F surface dewpoints will be in place ahead of the eastward-advancing cold front. This will support MLCAPE to around 1500 J/kg amid effective shear values around 30-40 kt. Modest midlevel lapse rates and elongated/straight hodographs suggest sporadic hail near 1 inch will be possible with strongest cells. Locally strong/damaging gusts also may accompany the strongest activity. ...Leitman.. 08/12/2023 $$ = = = 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) .