Subj : DAY2SVR: Nws Storm Prediction Center Norman Ok To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Apr 20 2023 17:27:12 ACUS02 KWNS 201727 SWODY2 SPC AC 201725 Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1225 PM CDT Thu Apr 20 2023 Valid 211200Z - 221200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FRIDAY INTO FRIDAY EVENING ACROSS PARTS OF THE UPPER OHIO VALLEY INTO LOWER GREAT LAKES...AND ACROSS PARTS OF THE UPPER TEXAS COAST INTO LOWER MISSISSIPPI VALLEY... ....SUMMARY... Strong thunderstorms on Friday may impact parts of the upper Ohio Valley into lower Great Lakes region, and the upper Texas coastal plain into lower Mississippi Valley, accompanied by at least some risk for severe weather. ....Synopsis... Models indicate that a more prominent blocking regime will continue to evolve across eastern North America into the northwestern Atlantic through this period and beyond. As a result, it appears that amplified mid-level troughing across the Great Plains and Mississippi Valley early Friday will make only slow further eastward progression across and east of the Mississippi Valley through early Saturday. The center of an associated broad, modestly deep and occluding surface cyclone is forecast to gradually weaken across the Upper Midwest into adjacent Great Lakes region. However, it is possible that similar secondary surface cyclogenesis may commence by late Friday night across the Allegheny Plateau vicinity, as a couple of short wave perturbations pivot around a lingering mid-level cyclonic circulation across the Upper Midwest. An initial surface cold front advancing eastward through the Ohio Valley during the day Friday may provide the focus for the developing surface low. It appears that the trailing flank of the this front may slow and weaken across the lower Mississippi Valley through lower Rio Grande Valley vicinity, while a reinforcing cold intrusion makes progress through the lower Ohio/middle Mississippi Valleys and central Great Plains. At the same time, dry/potentially cool air, associated with surface ridging shifting off the south Atlantic coast, may be slow to lose influence across much of the Southeast. ....Upper Ohio Valley into lower Great Lakes vicinity... Pre-frontal boundary-layer moistening appears likely to remain rather modest. However, models suggest that a narrow corridor of stronger daytime boundary-layer heating and mixing will become sufficiently unstable to support at least scattered afternoon thunderstorm development, aided by favorable forcing for ascent downstream of the approaching large-scale mid-level trough axis. Based on forecast soundings the risk for severe hail appears negligible, but downward mixing of 30-50+ kt south-southwesterly flow (within the 850-500 mb layer) in convective downdrafts may contribute to at least some potential for damaging wind gusts into early Friday evening. ....Upper Texas coastal plain into lower Mississippi Valley... It appears that fairly extensive, but weakening, pre-frontal thunderstorm activity may be ongoing at 12Z Friday across parts of the lower Mississippi Valley into areas near or offshore of upper Texas coastal areas, in the presence of modest and/or weakening southerly lower/mid-tropospheric flow. With the Southeastern surface ridging also slow to lose influence, the extent of any subsequent severe weather potential for Friday remains unclear. Mid-level forcing for ascent associated with a notable short wave impulse forecast to pivot east-northeast of the southern Great Plains Red River Valley may be mostly glancing. However, with sufficient boundary-layer heating and destabilization, a pre-frontal corridor of strong to severe thunderstorm development appears possible Friday afternoon and evening, beneath strengthening westerly mid-level flow (50-70+ kt around 500 mb). This may include supercells posing a risk for large hail and some potential for a tornado. Due to lingering uncertainties, severe weather probabilities are currently being maintained at 5 percent. However, it is possible that probabilities could still be increased in later outlooks for this period, particularly across parts of central/northern Louisiana into central Mississippi. ...Kerr.. 04/20/2023 $$ = = = 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) .