Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu May 18 2023 04:55:04 ACUS01 KWNS 180455 SWODY1 SPC AC 180453 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1153 PM CDT Wed May 17 2023 Valid 181200Z - 191200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE SOUTHERN/CENTRAL PLAINS...THE UPPER MIDWEST...AND THE TENNESSEE VALLEY... ....SUMMARY... Strong thunderstorms may impact parts of the southern Great Plains, the Upper Midwest, and the Tennessee Valley this afternoon and evening. Isolated strong gusts and hail may accompany some of these storms. ....Upper Midwest... A closed upper low over south-central Canada early this morning is forecast to dig southeast across the northern Plains and Upper Midwest through early Friday morning. The surface reflection of this feature will remain modest, though a cold front extending from western MN into central NE around midday will develop east and south through the afternoon/overnight. Boundary layer moisture will remain modest with forecast dewpoints from the mid 50s to near 60 F, but this should be sufficient to aid weak destabilization ahead of the front. Steep low-level lapse rates and around 30 kt effective shear magnitude will foster perhaps bowing structures with isolated strong/locally damaging gusts possible for a few hours from late afternoon to early evening. ....Southern Plains vicinity... Somewhat neutral mid/upper height tendencies to perhaps modest ridging is expected to prevail south of the Upper Midwest trough and east of a more evident upper trough near Baja. However, most guidance shows a weak perturbation migrating east from the southern Rockies into the southern High Plains through the afternoon/evening. Boundary-layer moisture will remain rather modest for this time of year, with 50s to low 60s F dewpoints as far north as western KS/far eastern CO. Heating and modestly steep midlevel lapse rates will support afternoon MLCAPE values from 1000-2000 J/kg. Vertical shear will remain weak, but some increase in a 850-700 mb flow toward 00z could support 25-35 kt effective shear magnitudes. Clusters/transient supercells will pose a risk for strong outflow winds and marginally severe hail. Some guidance suggests thunderstorms could develop into a forward propagating cluster into western OK as the low level jet modestly increases. This could briefly increase strong gust potential before increasing boundary-layer inhibition related to nocturnal cooling ensues. ....TN Valley vicinity... Generally weak deep-layer flow will preclude organized convection across the Southeast today. However, a weakening shortwave trough will migrate across the region, with some strengthening of upper level winds forecast. A seasonally moist airmass will be in place and a zone of stronger differential heating is forecast across parts of northern/central AL. Forecast hodographs are modestly elongated as winds increase with height above 700 mb and effective shear magnitudes around 25 kt may support brief strong cells capable of hail. Steep low-level lapse rates and light 0-2 km winds also may foster a few strong downbursts. ...Leitman/Weinman.. 05/18/2023 $$ = = = 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) .