Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Aug 03 2023 12:50:09 ACUS01 KWNS 031250 SWODY1 SPC AC 031248 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0748 AM CDT Thu Aug 03 2023 Valid 031300Z - 041200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL GREAT PLAINS... ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK...AS WELL AS OVER PORTIONS OF THE TENNESSEE VALLEY REGION... ....SUMMARY... The most concentrated and intense severe threat, today into this evening, will be for thunderstorm gusts across parts of the central Great Plains. ....Synopsis... The dominant synoptic- to large-scale upper-air feature for this period will remain a persistent high over central/east TX, which is forecast to drift southward over that region through this period. A mean ridge will continue to extend from there northwestward across the central/northern High Plains to portions of SK, but will be penetrated by a few shortwave troughs of varying amplitudes. The most prominent of those perturbations is apparent in moisture- channel imagery over UT, and forecast to pivot northeastward then eastward across WY toward the Black Hills through 12Z tomorrow. A weaker, but at least as influential shortwave trough is evident over the San Juan Mountains, and should move slowly northeastward over CO today. This trough's midlevel vorticity field should be convectively reinforced tonight across KS -- perhaps in the form of a distinct MCV. Farther north and east, a mean trough will persist from QC southward across or just east of the U.S. East Coast. In the trailing northwest flow, a shortwave trough now over northwestern ON -- near Lake Superior -- will move over the Lower Great Lakes during the 03-09Z time frame, then pivot northeastward and weaken somewhat. At the surface, 11Z analysis showed a low near STL, with warm front southeastward across central KY and mid/eastern TN to northeastern GA. A stationary front was drawn from the STL low west- southwestward across central KS to another low near DDC, with a weak cold front southwestward over northern NM. The eastern low should move eastward across KY today, while the trailing frontal segment sags southward over western KY/southern MO, largely behind an area of convective outflow over parts of the Tennessee Valley region. The front should move slowly southward over KS, then into northern OK overnight, with a parallel low-level moisture axis/plume to its immediate north across KS. ....Central Plains... Widely scattered to scattered thunderstorms are expected to form this afternoon on the eastern slopes of the Front and Laramie Ranges and move eastward across the adjoining High Plains. Large hail and damaging gusts each will be threats in the first few hours. With time, activity should consolidate into a quasi-linear band of outflow-dominant thunderstorms, producing swaths of severe wind. The greatest potential concentration and intensity of the wind threat appears to be either side of the I-70 corridor from eastern Co into western KS, perhaps as far north as I-80 in portions of southwestern NE, with the southern part encountering greater buoyancy and lasting longer. The 30%/enhanced wind area has been expanded eastward somewhat to account for forward-propagational, cold-pool driven potential for severe gusts this evening. Activity should develop as large-scale ascent aloft -- immediately preceding the ridge-penetrating shortwave trough(s) -- times well to move atop a diurnally heated/destabilizing and favorably moist boundary layer from the foothills eastward. A deep, well-mixed boundary layer across eastern CO should foster strong-severe gusts relatively early in the convective cycle, in addition to supporting survival of hailstones to the ground. A moist axis and easterly surface-wind component will be present across eastern CO and much of KS, with favorable storm-relative winds for an accelerating MCS this evening. Preconvective MLCAPE should range from around 1500-2000 J/kg over eastern CO to 2500-3500 J/kg over central KS, though MLCINH also will increase with eastward extent and time, requiring more forced/cold-pool-driven ascent to maintain the convection at severe levels. Additional, isolated to widely scattered thunderstorms also may develop ahead of the MCS and north of the front this evening, near the surface moist axis, posing a threat for isolated severe hail and/or gusts from eastern KS into parts of MO. ....Parts of the TN Valley/Southeast... Scattered thunderstorms are expected to cross this region today from northwest-southeast -- generally following the ambient flow west of the mean mid/upper trough, as well as a net baroclinic zone southwest of the synoptic warm front related to successive convective outflows. While some timing uncertainty remains, the activity over this region will have the potential to produce damaging to severe gusts. The tornado threat is very conditional, tied mainly to storm-boundary interactions on or near the main baroclinic corridor. An ongoing band of strong thunderstorms across northwestern TN may be an early manifestation of the day's severe threat farther southeast, if it can last long enough for the foregoing air mass to diurnally destabilize favorable. See SPC mesoscale discussion 1819 for near-term/nowcast details. Whether ahead of this or later activity developing on its outflow-reinforced boundary, the severe threat will be supported by rich low-level moisture, with surface dewpoints in the upper 60s to mid 70s F being widespread from the boundary southward to the Gulf Coast. That, along with strong heating and a deep troposphere, should offset modest midlevel lapse rates to drive MLCAPE into the 2500-4000 J/kg range on the warm (southwest) side of the boundary. Low-midlevel winds and shear will be weak, suggesting multicellular clusters will be the predominant mode, with some upscale/cold-pool growth possible. ....Parts of lower MI into NY... The extent of destabilization later today over NY is uncertain -- behind ongoing cloud/precip. Still, sufficient boundary-layer heating and large-scale lift should occur ahead of the Canadian shortwave trough to support additional development with a primary damaging-wind concern. Although most progs reasonably indicate greater buoyancy over Canada, a plume of minimally inhibited, 1000-1500 J/kg MLCAPE may develop across eastern Lower MI and northern NY, supporting convective potential along/ahead of a cold front preceding the trough aloft. The greatest unconditional threat across the U.S. part of the region appears to be over parts of northern NY, where relatively concentrated/focused activity at severe levels may move across from southern QC this evening. Modest and nearly unidirectional low/middle-level wind profiles will keep effective shear weak, though strong upper-level flow will aid in convective organization. Potential becomes more isolated and conditional farther south in upstate NY, as well as over Lower MI. ...Edwards/Broyles.. 08/03/2023 $$ = = = 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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