Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Apr 06 2023 12:54:52 ACUS01 KWNS 061254 SWODY1 SPC AC 061253 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0753 AM CDT Thu Apr 06 2023 Valid 061300Z - 071200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF THE MID-ATLANTIC REGION... ....SUMMARY... Damaging thunderstorm gusts and isolated large hail are possible over portions of the Mid-Atlantic region this afternoon. ....Synopsis... In mid/upper levels, a cyclone now located over northwestern ON will eject northeastward across the southern Hudson/northern James Bays through 00Z, while weakening, then become an open-wave trough over northern QC overnight. The trailing synoptic-scale trough will follow the cyclone northeastward through the period, moving across the Upper Great Lakes while also weakening substantially. In its wake, height rises are expected over most of the southern and central Plains, while modest falls will occur over the Mid-Atlantic and Northeast under the trough's glancing/southeastern influence. A southern-stream trough is apparent in moisture-channel imagery over southern CA and northern Baja, southward over Pacific waters west of central/southern Baja. This trough is expected to move only slowly eastward through the period, reaching Sonora and the southern Gulf of California by 12Z tomorrow. Despite broader-scale height rises, the southwesterly flow to the trough's east (across south Texas) will be traversed by a series of minor vorticity lobes -- some convectively enhanced or generated. At the surface, 11Z analysis showed a cold front from northern NY southwestward across western PA, the OH/WV border region, eastern parts of KY/TN, and southwestern MS, becoming quasistationary across southwestern LA Gulf shelf waters off the TX Coast. By 00Z, the cold front should extend from southeastern New England across eastern VA, northern GA, and southern parts of MS/LA, becoming quasistationary across waters near the TX Coast, not far from present position. Slight southward shift of the western Gulf Coast segment of the front is possible late in the period with some reinforcing cold advection to its north, but overall, little movement is expected. Meanwhile, by 12Z, the front should clear all the Atlantic Coast north of southern NC. ....Mid-Atlantic and vicinity... Scattered thunderstorms are expected to develop along/ahead of the front this afternoon -- mainly over the Piedmont region to Fall Line -- atop an increasingly moist, diurnally unstable and weakly capped boundary layer. This activity should move generally east- northeastward across the outlook area, offering mainly damaging gusts, with isolated large hail also possible. Surface dewpoints in the low/mid 60s F should become common across most of the Delmarva Peninsula, MD, VA and NC from the Piedmont to the Coastal Plain and Tidewater regions through the day. This in concert with unsteady but progressive diurnal heating under patchy cloud cover, will contribute to MLCAPE generally in the 1000-1500 J/kg range. Gradient flow aloft, beneath the aforementioned slight height falls, should help to sustain 40-50-kt effective-shear magnitudes, despite southwesterly surface flow and lack of directional change with height. This will support a mix of multicell clustering, quasi-linear and at least transient supercell modes as activity moves toward the coast late this afternoon into early evening. Steep low-level lapse rates associated with the heating/mixing process will augment strong-severe gust potential under the best-organized activity. The western/northern parts of the outlook areas were reoriented somewhat to conform closer to the geometry of the expected convective-initiation zone. ....South TX to southeastern LA/southern MS... Episodes of widely scattered to scattered thunderstorms are expected throughout the period over south TX, with isolated severe hail possible. As with a swath of convection/precip now apparent from between MFE-LRD northeastward past the UTS area, the main forcing for ascent should be the elevated frontal surface, overlain by sporadic shots of DCVA with the subtle vorticity lobes mentioned above. Changes in height of that frontal surface, and of the UVV along it, may lead to LFC at somewhat higher or lower levels than where the main band currently is located, indicating some convective potential either closer to or farther from the surface front as well. Low-level moisture transport and warm advection will continue to supply favorable inflow-layer theta-e for this activity, whose somewhat dense and messy modal character will inhibit even greater severe potential, despite favorable deep shear. Forecast soundings reasonably indicate around 1000-1500 J/kg peak MUCAPE (locally higher) rooted generally between 700-850 mb, amidst 45-60 kt effective-shear magnitudes. This suggests that wherever cells can sustain relatively undisturbed inflow long enough to mature, storm-scale organization/rotation is possible above the stable low levels, locally increasing hail potential. Isolated strong gusts or near-severe hail cannot be ruled out farther east over southeastern LA or southern MS near the front, especially on the warm side where a diurnally heated/mixed boundary layer will be present. However, in the absence of substantial mid/upper-level support and related low-level mass adjustments, hodographs will remain small, with around 35 kt effective-shear magnitudes, and uncertainties on coverage of thunderstorms. For now, potential appears non-zero, but too conditional for a categorical outlook area. ...Edwards/Smith.. 04/06/2023 $$ = = = 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) .