Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed May 31 2023 12:58:00 ACUS01 KWNS 311257 SWODY1 SPC AC 311256 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0756 AM CDT Wed May 31 2023 Valid 311300Z - 011200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF THE SOUTHERN HIGH PLAINS... ....SUMMARY... Large, damaging hail, severe gusts and a few tornadoes are possible this afternoon and evening over portions of the southern High Plains. ....Synopsis... In mid/upper levels, a rather messy/chaotic pattern with weak flow will persist over most of the CONUS east of the Rockies, characterized by broad/diffuse troughing and associated cyclonic flow over the Southeast and Gulf, an anticyclone over the Northeast and weak, MCV-penetrated ridging over the southern/central Plains. Mean troughing will persist over the West Coast States, while a compact, basal cyclone -- initially centered over southern CA -- shifts east-northeastward over AZ. The surface pattern remains rather ill-defined east of the Rockies as well, except for two potentially influential features: a dryline drawn at 11Z from eastern Chihuahua northward over far west TX, east-central NM, eastern CO, near the WY/NE border and Black Hills. This feature will shift erratically through the day due to a combination of mixing and advective processes, as well as interaction with convective outflows. A lee trough was drawn (and should remain) near the dryline over most of that length. One prominent outflow boundary arched across west-central OK, northwest TX and the South Plains near LBB, then over eastern NM to near LVS. With ongoing /reinforcing outflows over the Panhandle at this time, some additional southward/westward motion is possible over the southern High Plains before the boundary stalls around midday, and retreats northeastward late this afternoon into evening. ....Southern High Plains... Multiple rounds of thunderstorms will affect the region through the period, with at least marginal severe coverage/magnitude possible. The greatest severe threat appears to be this afternoon into evening over eastern NM, spreading into adjoining parts of TX and the OK Panhandle this evening and tonight. All severe modes are possible, including isolated significant-severe hail and wind, and -- especially near the boundary in NM where remnant low-level vorticity is maximized -- a tornado or two, with any sustained, relatively discrete supercells. Wind potential may be most intense and organized as activity grows upscale and moves into the TX Panhandle this evening. An ongoing area of elevated convection, with a few intermittently strong thunderstorms, is apparent over the central/southern TX Panhandle, behind the outflow boundary. This activity also is reinforcing baroclinicity with the cold pool, and keeping the boundary progressive for the time being. Brief pulses of post- outflow convection to marginally severe levels (for hail) are possible over the next few hours. Isolated strong-severe thunderstorms also may occur later this morning through midday across parts of north-central/northeastern NM, associated with a plume of UVV now supporting non-severe convection in the ABQ vicinity. As this ascent moves east of the Sandias and over the southern Sangre de Cristos, and the dryline effectively backs into the mountains over part of this region (with aid from easterly outflow), thunderstorms may build in strength and coverage, offering isolated severe hail and/or strong gusts before moving into more-stable outflow air across the RTN/CAO corridor. Scattered thunderstorms should develop this afternoon over eastern NM near the outflow boundary, along orographic/upslope-lift areas just to its north where easterly components are largest, and near the lee trough/dryline in areas of strong surface heating and diurnally minimized MLCINH. Some of these may become supercells atop a favorably moist inflow layer (dewpoints mid 50s to low 60s F) and amidst an increasingly well-sheared wind profile. Veering of winds with height, hodograph size, and low-level SRH, should be greatest along and just north of the boundary, but deep shear and environmental southeasterlies will contribute enough to the wind profiles to favor supercells to its south as well. Gradually strengthening and difluent mid/upper-level flow will spread across much of NM through the period ahead of the CA/AZ cyclone. This area also will come under the left-exit region of a cyclonically curved subtropical-jet (STJ) segment, contributing to large-scale ascent aloft. At 250 mb, the STJ axis/max itself will be close to the international border; however, sufficiently strong upper-level flow to support favorable deep shear should extend northward near or even somewhat past I-40. Meanwhile, low-level warm advection will increase ahead of the mid/upper cyclone, aiding evening recovery of the air mass across northeastern NM and the Panhandles ahead of the convection moving northeastward out of NM, and helping to maintain severe potential into tonight as activity aggregates upscale. ....Central High Plains... Isolated to locally scattered thunderstorms are expected to form this afternoon near the dryline/lee trough and on higher terrain features, such as the Black Hills, Rockies foothills and eastward- extending ridges. Isolated severe gusts and hail are possible. The foregoing diurnal boundary layer will be well-mixed with steep lapse rates of at least 9 deg C/km, yet still somewhat moist for the elevation with 40s and 50s F surface dewpoints. This will support areas of widely variable MLCAPE, but generally 1000-2000 J/kg, along with large DCAPE, conducive for locally severe downdrafts. Southeasterlies are expected in much of the preconvective near-surface layer from about I-70 northward, enhancing low-level storm-relative winds. However, mid/upper-level flow will be considerably weaker than over the southern High Plains, keeping deep shear modest. The dominant mode, therefore, should be multicellular. Within the broader 5% wind area, embedded pockets/ swaths of greater gust potential may develop, where activity can aggregate smaller cold pools into an organized/persistent cluster. However, mesoscale uncertainties preclude a more-focused/smaller corridor of greater unconditional potential at this time. ...Edwards/Jewell.. 05/31/2023 $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. 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