Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Feb 09 2023 12:48:48 ACUS01 KWNS 091248 SWODY1 SPC AC 091246 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0646 AM CST Thu Feb 09 2023 Valid 091300Z - 101200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ALONG THE NORTHEASTERN GULF COAST AND VICINITY...AND FROM PARTS OF THE OHIO VALLEY TO LOWER GREAT LAKES... ....SUMMARY... Isolated damaging thunderstorm gusts and a brief tornado are possible across the northeastern Gulf Coast and vicinity. Isolated severe gusts may occur from parts of the Ohio Valley to Lower Great Lakes. ....Synopsis... A progressive, highly amplified mid/upper-level synoptic pattern prevails, featuring a mean trough in the central CONUS. This trough will be maintained as one strong shortwave exits, and another enters. The exiting perturbation is apparent in moisture-channel imagery as a compact cyclone centered over eastern MO, with a negatively tilted trough from northwestern MO to southernmost IL. This feature should move northeastward to Lower MI by 00Z, before becoming entrained into northern-stream westerlies and turning eastward across southeastern Canada. Meanwhile, shortwave troughs now evident over the western Dakotas, and from southeastern WY across CO to the Four Corners, will phase/merge today. This will lead to a well-developed synoptic trough by 00Z from NE across southeastern CO and northeastern to southwestern NM. By 12Z, the trough should extend from central MO across OK to far west TX, at least temporarily phasing with a northern-stream perturbation digging southeastward to the western Upper Great Lakes region. At the surface, 11Z analysis showed a 996-mb low near UIN, with occluded/cold front arching across western KY, the MS/AL border region, to southeastern MS, southeastern LA, and the northwestern Gulf. The cold front is expected to proceed northeastward up the Ohio Valley and lower Great Lakes through the period, while crossing the central/southern Appalachians. By 00Z, the front also should reach southeastern AL, the western FL Panhandle, and the north- central/west-central Gulf. By 12Z, the front should reach the western Carolinas, central GA and the central FL Panhandle. ....Northeastern Gulf Coast and vicinity... Satellite and composite-radar trends indicate a broad, weakening area of mainly residual showers, with isolated lightning still possible, within about 60-90 nm behind an outflow boundary analyzed from near CSG-DHN-DTS and southwestward over the Gulf, between the Mississippi River mouth and rig station KIKT. This activity no longer offers a severe threat, and is expected to continue gradual breakup/dissipation through the remainder of the morning as it moves into unfavorably stable low and middle-level profiles somewhat similar to those sampled by the 12Z TLH sounding farther east. Scattered to widely scattered thunderstorms are expected to develop from midday through afternoon tonight -- both in the wake of the morning convective band near the cold front, and perhaps along part of the residual outflow boundary near/over the Gulf, where return of some favorably modified marine boundary layer will have occurred. The most vigorous few cells may pose an isolated threat of damaging to marginally severe gusts or a brief tornado. Modest prefrontal diurnal heating (limited in extent and duration by lingering cloud cover), combined with low-level warm and moist advection in the return-flow sector behind the morning precip, will contribute to steepening of low-level lapse rates. Meanwhile, time series of forecast soundings show a degree or two C cooling of mid/upper-level lapse rates. Overlaid, these processes yield around 500-1000 J/kg MLCAPE for dewpoints generally recovering into the mid/upper 60s F. Though substantial deep-layer lift will remain well north and northwest of the area, weak MLCINH, combined with loft along the front and prefrontal boundaries, will support convective development. Modest boundary-layer flow will limit hodograph size, but sufficient mid/upper flow will remain to support areas of 30-40-kt effective-shear magnitudes. ....Ohio Valley to Lower Great Lakes... A low-topped band of strongly forced convection is evident this morning in an arc near the cold front, from eastern IL across western KY to northwestern middle TN. The strongest part of this band should cross portions of IN, OH, and perhaps southern Lower MI through the day, offering a threat for damaging to isolated severe gusts. Most of this activity will have no thunder, with forecast soundings suggesting MUCAPE less than 500 J/kg just below icing layers suitable for lightning generation, or barely extending into that thermal stratum. Though vigorous low-level theta-e advection will lessen its depth, a near-surface stable layer is likely to be maintained over most of the area, rendering the wind threat sporadic and isolated, where only the most vigorous downdrafts can transfer enough momentum down from strong low/middle-level flow to punch gusts at or near severe limits through to the surface. ...Edwards/Leitman.. 02/09/2023 $$ = = = 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) .