Subj : Enhanced Risk Plains To : All From : Dumas Walker Date : Fri May 24 2024 08:27 am ACUS01 KWNS 241256 SWODY1 SPC AC 241255 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0755 AM CDT Fri May 24 2024 Valid 241300Z - 251200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS MORNING OVER PARTS OF EASTERN IOWA AND NORTHERN ILLINOIS...AND THIS AFTERNOON TO EVENING OVER PARTS OF EASTERN OKLAHOMA AND NORTH-CENTRAL/CENTRAL TEXAS... ....SUMMARY... Enhanced threat corridors exist for severe thunderstorm gusts this morning from eastern Iowa over northern Illinois, and hail (some very large) this afternoon and evening from eastern Oklahoma to north Texas. ....Synopsis... In mid/upper levels, a progressive shortwave train should continue within a belt of mostly westerly flow aloft over the CONUS. The strongest of these shortwave troughs is evident in moisture-channel imagery over the northern Great Plains, with an embedded 500-mb low over northwestern SD. The low should follow a cyclonically curving, net northeastward path to the northeastern corner of ND by 00Z, with trough roughly southward along the western border of MN then over eastern NE. By 12Z tomorrow, the CONUS part of the trough should arc from western Lake Superior across eastern WI and northern IL. Over the Southeast, a broad area of difluent mid/upper flow is expected, with numerous embedded vorticity lobes (some convectively generated or enhanced). Fairly unperturbed west-southwesterly flow is expected from the Arklatex region across the southern Plains and Desert Southwest, downstream from a trough off coastal CA. The surface analysis at 11Z showed a low over southeastern ND, with occluded/cold front arching across southwestern MN, western IA, east-central KS, west-central OK, TX between PVW-LBB, and northeastern NM. A warm front was drawn from the leading edge of a severe MCS over eastern IA, southeastward across central IL. The low should occlude and shift northward over southeastern MB through the period. By 00Z, the frontal triple point should reach southern WI, with cold front across western IL, southwestern MO, southeastern OK and north-central to west-central TX, becoming a warm front over east-central/northeastern NM. The warm front will move northeastward to southern WI and southwestern Lower MI, though its definition may be compromised by the effects of MCS activity. A dryline was apparent from its frontal intersection over northwest TX south-southwestward to the Big Bend region. This boundary will mix eastward today while the front overtakes it from the north, and should reach the eastern Edwards Plateau/western Hill Country by late afternoon. ....Southern Plains to Mid-South... Scattered thunderstorms -- including supercells -- are expected to develop near the front this afternoon, to the east and northeast of the dryline. Dryline storm-initiation potential is more conditional and isolated. Once development occurs, updraft growth and storm evolution may occur very rapidly, given the strong surface heating, abundant moisture (70s F dewpoints common), steep deep-layer lapse rates and intense buoyancy (4000-5000 J/kg MLCAPE) that should develop. Low-level flow and hodograph size will be modest, amidst a lack of substantial mid/upper-level perturbations to force greater mass response. However, ambient mid/upper winds will be strong enough to support supercells (left- and right-moving), with effective-shear values near 50 kt. Large to very large hail should be common in the first few hours after initiation, and locally severe gusts are expected as well. Airmass recovery is possible into southeastern and east-central OK in the zone of warm/moist advection ahead of the front, and behind last night's southeastern OK activity. A relatively dense and enhanced concentration of hail potential from eastern OK into north-central TX is expected, with hailstones greater than 2 inches in diameter likely, and some hail perhaps exceeding 3 inches. Otherwise, deep, precip-loaded downdrafts will provide most of the wind potential early, with some upscale clustering and cold-pool aggregation possible to maintain damaging- wind potential into late evening, before activity generally weakens. ....Midwest... Enhanced potential for severe gusts, along with a risk of a few brief/embedded tornadoes, may persist for a few more hours with an ongoing complex of thunderstorms crossing portions of eastern IA and northern MO, as this activity moves into IL and perhaps southern WI. A well-developed rear-inflow jet of 60-80 kt has been sampled by DMX radar VAD wind profiles. The northern part of the complex is expected to weaken as it penetrates deeper into the cool sector (north of the warm front), while the middle part may persist for several hours near the front and across IL. See SPC Severe Thunderstorm Watch 300-301 and related mesoscale discussions for near-term details. The outflow boundary from this complex was analyzed ahead of the cold front across parts of northwestern MO into northeastern KS, and should be laid down through the remainder of the morning across the rest of northern MO and parts of northern IL. Given the deep and well-organized nature of its cold pool, severe probabilities may be more associated with the present activity. Later development becomes more doubtful with northward extent from the boundary, which may retreat somewhat northward into southeastern IA and toward the WI/IL line later this afternoon, prior to frontal passage. Probabilities mainly reflect the ongoing hazard, however, given great uncertainties regarding airmass recovery behind it. Farther southwest along/ahead of the front, widely scattered to scattered afternoon thunderstorms are possible, offering damaging gusts and large hail, as well as marginal tornado potential. A substantial uncertainty regarding airmass recovery also is present in this regime, because of trajectories emanating from a pronounced theta-e deficit in AR and eastern OK produced by prior overnight convection. A narrow corridor of sufficient boundary-layer moisture to support 2500-3500 J/kg MLCAPE may develop just ahead of the front. Some relative flow weaknesses progged in parts of the mid/upper troposphere may render somewhat messy storm structures after early supercell mode. Still, any storm(s) interacting with the outflow boundary will have locally greater potential for supercell longevity, and some risk for large to significant hail and a tornado. ...Edwards/Goss.. 05/24/2024 $$ --- SBBSecho 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (21:1/175) .