Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Feb 27 2023 12:58:26 ACUS01 KWNS 271258 SWODY1 SPC AC 271257 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0657 AM CST Mon Feb 27 2023 Valid 271300Z - 281200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF ILLINOIS ACROSS MUCH OF OHIO... ....SUMMARY... Thunderstorms may produce damaging gusts across the Ohio Valley today. At least a few tornadoes are also possible, especially across Ohio this afternoon. ....Synopsis... A substantial mid/upper-level trough -- with several embedded shortwaves and vorticity maxima -- will move eastward over the coastal Pacific Northwest and northern CA through the period, contributing sufficient low/middle-level instability to support general thunder potential there. A downstream, progressive, split-flow pattern is apparent, with the split related to a strong shortwave trough and embedded/intermittent cyclone now over MO/IA. This perturbation should move east-northeastward across IL, IN, OH, and western/northern KY through 00Z, with substantial weakening thereafter into the Mid-Atlantic. The associated surface low was analyzed at 11Z over northwestern MO, with cold front arching across southeastern MO, central AR, to south-central TX. A warm front was drawn across southern IL to eastern TN. The warm front will shift northeastward diffusely/erratically today through the Ohio Valley, given counterbalancing effects of : 1. Areas of precip to its north, but also 2. Intense low-level warm advection atop the shallow-sloped frontal surface, in the vigorous mass response to the mid/upper trough. By 00Z, the surface low should reach southern Lake Michigan in occluded form, with another low close to the mid/upper trough over northern OH, and warm front southeastward over southwestern PA. The cold front should extend into south-central OH, the southern Appalachians, western AL, central MS, and central LA, becoming quasistationary and somewhat frontolytic from the Delta region west-southwestward. By the end of the period, either warm-frontal movement or reformation farther north is expected for the western lobe of the frontal zone, into a low developing across northwestern OK. ....Ohio Valley region... Multiple episodes of thunderstorms are expected across the area through afternoon, beginning with elevated, non-severe precip and isolated to widely scattered embedded thunderstorms now over parts of WI, central/northern IN, southwestern MI, to western OH. Behind this activity, an initially loosely organized arc of precip/showers and isolated thunderstorms was evident ahead of the cold front, and crossing the warm front, over parts of central/southern IL to western KY. This activity -- the remnants of the previous days' damaging MCS over the southern Plains and Ozarks -- will proceed east-northeastward through the region into a weakly destabilizing airmass today. That destabilization will result from both warm advection/frontal passage and very muted diurnal heating, which in combination with strengthening deep-layer winds/shear, may help to organize this activity better. Isolated damaging gusts would be the main concern. Finally, an arc of relatively low-topped convection is possible nearer to the cold-core region of the mid/upper perturbation this afternoon, sweeping eastward over portions of IN/OH into a very narrow plume of destabilization behind the previous convective round. Damaging gusts and a couple tornadoes are possible. MLCAPE in the 200-700 J/kg range may develop, amidst hodographs that will be shrinking with time but still favorably large to support supercell and bow-echo potential. The most-favorable parameter space still appears to be possible over parts of eastern IN into central/southern OH this afternoon. As often is the case with the northern (poleward) and eastern (downshear) parts of wind outlooks in particular, considerable mesoscale uncertainty exists on when (and how much) MLCINH becomes "too much" to permit substantial momentum transfer through weak low-level lapse rates to the surface. Once the weakening of convection occurs, it could be rapid, given the nocturnal stabilization in the evening, weakening of the parent mid/upper trough after 00Z, and nearly negligible buoyancy progged over those fringe areas. Current indications are that the unconditional potential will decrease toward Lake Erie and western PA. Somewhat more buffer was given between the 5% and 15% areas by some modification of the latter, and this may continue in succeeding outlooks if progs and/or mesoscale diagnostics trend slower and/or more westerly with the bulk of gust threat. ...Edwards/Kerr.. 02/27/2023 $$ = = = 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) .