Subj : DAY1SVR: Enhanced Risk To : All From : Mike Powell Date : Sat Jul 29 2023 08:47:00 ACUS01 KWNS 291300 SWODY1 SPC AC 291259 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0759 AM CDT Sat Jul 29 2023 Valid 291300Z - 301200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF SOUTHEASTERN NEBRASKA TO NORTHWESTERN MISSOURI... ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK...EXTENDING SOUTHEASTWARD TOWARD THE EASTERN OZARKS/SOUTHERN IL REGION...AS WELL AS FROM PORTIONS OF THE CENTRAL APPALACHIANS AND MID-ATLANTIC TO NEW ENGLAND...AND IN TWO SEPARATE AREAS OVER PORTIONS OF THE CENTRAL AND NORTHERN GREAT PLAINS... ....SUMMARY... Widely scattered to scattered strong to severe thunderstorms are possible over southern New England into the Mid Atlantic states on Saturday. A few strong/severe storms may also be noted across the central High Plains. Damaging gusts are the primary hazard, though hail is possible across the Plains. ....Synopsis... In mid/upper levels, a persistent, strong anticyclone will persist over the southern Rockies, with prominent ridging across the southern Plains to the lower Mississippi Valley region. Another ridge -- extending northwestward through the Central/northern Rockies -- will amplify through most of the period. Downstream, a belt of northwest to west-northwest flow aloft will persist from much of MT to the Upper Great Lakes and much of the Ohio Valley, where the flow aloft becomes more difluent. The mean trough and associated cyclonic flow will continue to cover much of the eastern CONUS, with the strongest flow over the Lower Great Lakes to New England, and northern Appalachians. An embedded, convectively reinforced shortwave trough -- apparent in moisture-channel imagery from southwestern ON to northern KY -- will pivot eastward across the northern Mid-Atlantic region to western New England through 00Z, with some weakening possible. At the surface, 11Z analysis showed a low near the northern shore of Lake Erie in southern ON, with cold front southwestward to another low over north-central MO, then westward over northern KS. An extensive outflow boundary south of the front -- from western PA across western WV and much of KY -- will decelerate with the cold front catching up, and the combined baroclinic zone becoming more prominent through the day. The eastern low should move/redevelop eastward along the frontal zone, crossing the inland northern Mid-Atlantic today and southern New England this evening, followed by the cold front. ....Central Plains to lower Missouri Valley/lower Ohio Valley... A well-organized MCS is crossing parts of central/southern NE with well-developed cold pool apparent in surface obs, rear-inflow jet in radar-velocity imagery, and history of several measured-severe gusts. Refer to the remainder of SPC Severe Thunderstorm Watches 565, 566 and related mesoscale discussions for near-term coverage of the threat. Guidance has been inconsistent -- including most CAMs, which have not been particularly reliable on this MCS outside perhaps the 00Z NSSL WRF, which depicted this, but was too slow. This includes some forecasts of a potential temporary weakening over northern MO, which is possible, but for which uncertainty is too great to attempt an unconditional break in spatial probabilistic continuity. In either event, the associated pressure/UVV perturbation may lead to a continuation or invigoration of severe potential over eastern MO into parts of the lower Ohio Valley, perhaps as far as the Tennessee Valley, near both the outflow-reinforced baroclinic zone and low-level moist axis. Rich low-level moisture, with surface dewpoints in the upper 60s to low 70s F, will continue to be available in the projected track, as well as a diurnally heated/destabilizing airmass from midday into afternoon. Accordingly, severe-wind probabilities have been introduced, and isolated significant-severe gusts cannot be ruled out. ....Central/Northern High Plains... Previous outlook reasoning still appears valid at this time for the central High Plains part of the outlook, which should be well west of the stabilizing influence of the MCS now crossing parts of the lower central Plains. However, farther north across the northern High Plains, concern has increased for the threat of supercells to develop this afternoon across the eastern MT/western Dakotas corridor, near and just east of a surface boundary and near a low-level moist axis. This activity should move southward to southeastward, offering severe hail (some potentially above two inches in diameter where inflow-layer buoyancy/moisture should be greatest), and isolated severe gusts. Strong veering of winds with height will lead to a long, somewhat hook-shaped low-level hodograph with small near-surface SRH, but strong total shear and deep shear (effective-shear magnitudes 50-60 kt over western SD decreasing to 40-50 kt farther north). Buoyancy also will be favorable in this corridor, but decreasing northward, with MLCAPE ranging from the 2000-3000 J/kg range near the moist axis just north of the Black Hills, to less than 1000 J/kg near the international border. Convection should diminish this evening as inflow-layer instability weakens. ....Northeastern CONUS... The remnants of an MCS, that produced several measured severe gusts and numerous damage reports in the southern Upper Great Lakes region overnight, appear to be weakening while moving into a more-stable environment in western/central PA. Rejuvenation of this activity -- or additional development in the associated plume of relatively maximized deep-layer ascent preceding the shortwave trough -- will lead to a ramping up of severe potential from midday into this afternoon across much of the Northeast. A favorably moist and diurnally destabilizing airmass will support thunderstorm development from this regime southward over the eastern parts of the higher terrain, and the Piedmont, with occasional damaging gusts as the main threat. ....AZ... Widely scattered thunderstorms may develop this afternoon over higher terrain north through southwest of TUS, shifting westward to southwestward across lower deserts of southern AZ. Isolated severe gusts will be the main concern. A deep layer of easterlies from about 700 mb to the max parcel level will encourage this activity out of the mountains and over hot, deeply mixed, lower-elevation boundary layers. Just enough moisture may remain through the mixing process to support 200-800 J/kg MLCAPE above, and 2-3 times that much DCAPE. With modest buoyancy, the longevity and organization of the potential is in question, so the severe threat remains at an unconditional marginal level. ...Edwards/Broyles.. 07/29/2023 $$ --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .