Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Sep 07 2023 12:44:11 ACUS01 KWNS 071244 SWODY1 SPC AC 071242 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0742 AM CDT Thu Sep 07 2023 Valid 071300Z - 081200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE MID-ATLANTIC AND NEW ENGLAND... ....SUMMARY... Potential for locally damaging wind gusts and marginal hail will be possible across the Northeast, and southwestward into the Southeast. Gusty winds and hail may also occur locally over parts of the central and southern Plains and Arklatex area. ....Synopsis... The mid/upper-level pattern will be characterized by a progressive northern stream, along with amplification of western mean ridging and eastern troughing through the period. A shortwave trough now over the Upper Great Lakes should move slowly eastward to northeastward and weaken gradually. However, in the northwest-flow belt to its southwest, another well-developed perturbation -- now over the lower Ohio Valley and AR -- will intensify as it moves toward the southern Appalachians and Tennessee Valley region today. By 00Z, the trough should be near an axis from JKL-CHA-SEM, then to an AVL-MCN-AAF axis by 12Z. Farther northwest, another shortwave trough -- evident in moisture- channel imagery over portions of WY -- should pivot east- southeastward out of the building mean ridge, and reach near a PIR-OGA-ITR axis by 00Z. The trough then should turn southeastward, reaching IA, northern MO and eastern KS by the end of the period. The 11Z surface analysis showed frontal-wave lows over southwestern QC and southern Lake Huron, with a cold front southwestward from the latter across eastern parts of OH/KY/TN, northern MS, and southern AR, becoming quasistationary westward over the Red River region to the TX Panhandle. The western segment of this boundary should move slowly northward over OK through the period, while the remainder shifts southward across northern/central LA, and southeastward over parts of AL/GA the western Carolinas, western/central VA, and central/eastern parts of PA/NY. A High Plains lee trough -- already well developed over the from eastern MT to northeastern NM -- will shift eastward to the Black Hills, western NE Sandhills and western KS through the afternoon. ....Atlantic Seaboard... Widely scattered to scattered thunderstorms -- both discrete and in forward-propagating small clusters -- may move northeastward over the outlook area from midday through early evening. Damaging to isolated severe gusts are the main concern, though a couple marginally severe instances of hail may occur also. Isolated to widely scattered, non-severe thunderstorms already are evident over higher terrain from western NY southwestward toward the KY/VA border region. The associated plume of large-scale lift and height falls aloft should develop eastward toward a surface trough closer to the coast, as: 1. The Great Lakes mid/upper trough shifts into more of ON, and 2. A weaker perturbation initially over the TN/VA border area and eastern KY ejects northeastward. Meanwhile, diurnal heating will destabilize a moist boundary layer, characterized by 60s dewpoints in higher elevations and northern areas, near 70 over the Tidewater to coastal Mid-Atlantic, and low-mid 70s F over southern parts of the "marginal" area where flow aloft and deep shear will be weakest. Cool midlevel temperatures and diurnally steepened low-level lapse rates will support essentially uncapped parcels with MLCAPE from 1500-2500 J/kg from parts of New England to southeastern GA. Somewhat stronger shear (though still supporting mainly organized multicells) is expected in the Mid-Atlantic and parts of New England. ....LA to OK... Isolated to scattered thunderstorms -- sometimes in semi-organized clusters -- may develop in two or three episodes through 12Z tomorrow. While mesoscale specific regarding storm coverage remain uncertain, the timing for these episodes generally appears to be: 1. Afternoon into early evening for development over LA, along and southwest of the front, and along and north of the sea breeze. Here, subtle lift aloft near the tail end of a midlevel vorticity lobe, and somewhat enhanced mid/upper-level gradient flow near the end of the shortwave trough, will aid in multicellular organization. Intense boundary-layer heating will support steep low/middle-level lapse rates, MLCAPE in the 1500-2500 J/kg range, and a well-mixed boundary layer enabling strong/isolated severe gusts and perhaps marginal hail to reach the surface. 2. An isolated conditional threat for damaging wind this afternoon near the front, in western/central OK. Coverage may be minimized by some capping combined with only weak frontal lift. However, any sustained convection that can form will have the potential for strong-severe gusts atop a deep, strongly mixed boundary layer. 3. Thunderstorms developing after 06Z in north-central/ northeastern OK and moving southeastward toward the Arklatex region. Wind speeds will be modest below anvil level (where 50-kt flow will support venting aloft); however, strong veering with height will contribute to 30-40-kt effective-shear magnitude. Isolated severe hail may be noted, especially relatively early in the local convective cycle before too much clustering occurs. Although forecast soundings indicate the layer of suitably moist inflow will be elevated (between 850-700 mb), isolated strong-severe gust potential will be supported by a residual, fairly deep mixed layer below cloud base and above the shallow near-surface cooling layer. ....Central Plains... Isolated to widely scattered thunderstorms are possible from the Black Hills southeastward, mainly late thus afternoon into early evening, as marginal moisture and strong surface heating underlie increasing large-scale ascent ahead of the WY shortwave trough. Isolated gusts/hail near severe limits will be the main concern. East of the trough, moist advection will offset vertical mixing enough to support surface dewpoints from the mid 40s in the west to mid 50s in the east, technically enabling surface-based parcels on a spotty basis. Most of the inflow-layer moisture and lift supporting convection should be above the surface, in a layer of high RH between 600-700 mb, with MUCAPE around 500-1000 J/kg. Still, with a well-mixed, rather dry environment from surface to 700 mb, any strong downdrafts (possibly with embedded hail) generated aloft may be maintained or accelerated to the surface. ...Edwards/Leitman.. 09/07/2023 $$ = = = 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) .