Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jun 17 2023 12:58:06 ACUS01 KWNS 171258 SWODY1 SPC AC 171256 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0756 AM CDT Sat Jun 17 2023 Valid 171300Z - 181200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM SOUTHEASTERN COLORADO TO NORTHWESTERN ARKANSAS... ....SUMMARY... Severe thunderstorms are possible over a vast area from Colorado to Florida, and central Texas to the lower Missouri Valley. Within that, a focused corridor of threat for damaging hail, severe to extremely severe gusts, and a few tornadoes, extends from southeastern Colorado to northwestern Arkansas. ....Synopsis... The mid/upper-tropospheric pattern will be characterized by western and eastern mean troughing. Split flow will continue in between, related to an unusually high-latitude subtropical jet across the southern Plains and lower Mississippi Valley. To its north, ridging over the mid/upper Mississippi Valley will weaken somewhat and move eastward toward the Great Lakes, as a series of shortwaves ejects across -- then away from -- the Rockies. This will occur while a cyclone over the Gulf of Alaska digs southeastward to Vancouver Island through the period, spreading height falls and strengthening mid/upper southwesterlies across the Pacific Northwest. The most important of the western shortwave troughs is evident in moisture-channel imagery from southwestern WY across southern UT to western AZ. This feature will pivot eastward, while becoming more compact and less positively tilted. By 00Z, the trough should reach eastern CO and northeastern NM, then should reach to near a line from STJ-PNC-FSI by 12Z tomorrow. In response, a preceding, convectively enhanced vorticity lobe -- now apparent in satellite and composited radar imagery from an MCV over south-central NE to parts of western/central KS -- will eject northeastward across western NE and western IA by 00Z. Farther east, a broad area of northwest flow aloft will cover much of the eastern CONUS and Gulf Coast, southwest of a cyclone covering parts of NY, QC and New England. Embedded shortwave troughs now include a convectively induced/enhanced feature over the northeastern Gulf just south of the FL Panhandle, as well as a perturbation over parts of northern AR and the Mid-South. These will move southeastward over the southeastern CONUS and northeastern Gulf through the period. At the surface, 11Z analysis showed a wavy, quasistationary to slow-moving cold front from near the FL/GA line across southern AL, central MS, the AR/LA border area, to north-central TX. This boundary should move little through the day. A dryline initially over eastern NM and the west TX Permian Basin should mix eastward/ northeastward through the afternoon, reaching west-central TX (Edwards Plateau/Big Country regions) and northwest TX. An outflow boundary is decelerating across the southern TX Panhandle, and is expected to retreat northward toward the northern TX/OK Panhandles and southeastern CO region through the day, amid low-level mass response to the approaching shortwave trough and related cyclogenesis over southeastern CO. By 12Z, the related low-pressure area should extend behind an MCS and along a cold front from eastern KS to north-central/west-central TX and southern NM. Warm frontogenesis is expected today from northern AL across parts of the Mid-South and northward over eastern IA/MN. ....Central High Plains to AR... A well-organized thunderstorm complex should develop and move southeastward out of southeastern CO this afternoon into evening, crossing much of northern/central OK and southern KS overnight, and perhaps reaching western AR by the end of the period. This activity may be preceded by (and also contain a few) supercells. All severe hazards are possible. A plume of large-scale ascent -- now supporting scattered showers and isolated thunderstorms from western CO to northeastern AZ -- will shift eastward through the Front Range by early afternoon. As this regime encounters a destabilizing and favorably moist boundary layer, heated to minimal MLCINH at elevated terrain of the foothills and especially Palmer Divide, scattered thunderstorms should develop and aggregate rather soon thereafter into a complex. Interrelated upscale convective growth and cold-pool expansion are expected, leading to a forward-propagational MCS that should yield severe-wind potential. This activity will move into a supercell-favorable environment of increasing low-level moisture and backed near-surface flow (veering and increasing with height, with long hodographs). This will foster potential for embedded supercells and bow/LEWP formations, with attendant all-hazard severe threat. Steep low/middle-level lapse rates and favorable moisture -- manifest as dewpoints in the 50s on the High Plains to mid/upper-60s F at lower elevations -- will contribute to inflow-layer MLCAPE of 2000-3000 J/kg (locally higher in the late afternoon). Strengthening difluence/divergence aloft also is expected in this region between the approaching shortwave trough and the left side of a more cyclonically curved subtropical-jet segment. Though more conditional, a threat for tornadoes and significant to very large hail exists with any supercells that can develop along or just north of the retreating boundary, near which the MCS also should track through this evening. A relative max in progged convergence ahead of the MCS, between southwestern KS and northwestern OK -- may indicate a relatively maximized discrete/pre- MCS supercell development zone. Additional bowing/surging of the MCS may occur locally with any precursory supercell(s) it overtakes and absorbs along the way southeastward, while the complex itself produces swaths of severe to significant-severe wind. QLCS mesovortices and tornado potential will exist in the southern KS/northern OK vicinity as the complex encounters a plume of rich boundary layer moisture and flow that is strong in both SRH and storm-relative inflow component. A complicating factor for defining severe potential on the southern end of the MCS will be an expansive outflow pool spreading northeastward into western/central OK from TX convection discussed below. Mesobeta-scale uncertainties exist on timing/location of this outflow's potential negative impact on MCS intensity. Further additional or persistent development on the northeastern edge of the cold pool may merge with the MCS over eastern/northeastern OK and the Ozarks late tonight. ....West-central/north TX, southern OK... Thunderstorms are expected to develop during mid/late afternoon along/ahead of the dryline and move eastward into this evening, with considerable aggregation and areal expansion likely toward north- central TX (including the DFW Metroplex) and southern OK. Severe hail (some greater than 2 inches across) is possible early in the convective process, when relatively discrete supercells are most probable. Severe to locally significant-severe (65+ kt) gusts also are expected with the resulting cold-pool expansion into north TX and southern OK. Northeastern parts of this activity may merge with the initially separate MCS tonight over eastern OK (discussed above). Activity should develop and grow atop a very well-heated/mixed boundary layer. Very steep low/middle-level lapse rates above 8 deg C/km will occur once remaining MLCINH is removed at the base of the EML, combining with rich boundary-layer moisture to support MLCAPE commonly exceeding 4000 J/kg. Deeply driven, water-loaded downdrafts cascading into a well-mixed subcloud layer will foster severe downdrafts and upscale organization/spreading of the outflow pool, perhaps reinforced by additional convection developing along then shifting atop the irregularly shaped arc of forced ascent. Environmental low-level winds will be modest, but veering with height, while strong venting aloft is expected beneath the main section of the subtropical jet, aiding in storm organization and spreading eastward motion. ....Southeast... Clusters of scattered to locally numerous thunderstorms are ongoing over northern FL, and expected to form over mainly the southern parts of the Gulf Coast States southeastward into the remainder of peninsular FL, south of the front. Damaging gusts and large hail are possible, with some hail potentially exceeding two inches in diameter over parts of the gulf Coast region, where supercellular character is more probable with the development under stronger mid/upper-level winds under the head of the subtropical jet. With rich low-level moisture (dewpoints mid 60s to near 80 F across the region) and minimal MLCINH amidst diurnal heating, activity should become most concentrated along: 1. Zones of enhanced large-scale ascent preceding the aforementioned shortwave perturbations, and 2. Sea-breeze, differential-heating and outflow boundaries. MLCAPE of 2500-4000 J/kg should be common, with effective-shear magnitudes up to 5o kt near the Gulf Coast. Deep shear will be weaker southeastward across FL, but with enough flow aloft to support organized multicells and perhaps transient supercells. ....Lower Missouri Valley vicinity... Scattered thunderstorms are expected to develop this afternoon over this region, in a loosely organized arc preceding the MCV, offering isolated severe hail and gusts. A meridionally oriented corridor of favorable boundary-layer theta-e and diabatic destabilization is expected from the warm frontogenesis region westward to near the MCV and trailing midlevel shortwave trough. Lack of a substantial EML over this region will foster weak diurnal MLCINH, but also modest mid/upper-level lapse rates, leading to peak/preconvective MLCAPE in the 1500-2000 J/kg range. A curving low-level convergence zone will impinge on the destabilizing, narrow warm sector, leading to the convection. With weak flow through much of the troposphere, vertical shear will be limited, with multicells as the dominant mode and only brief/transient supercell behavior possible. Activity should diminish with eastward extent this evening into a more-stable air mass. ...Edwards/Jewell.. 06/17/2023 $$ = = = 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) .