Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Sep 20 2023 12:48:34 ACUS01 KWNS 201248 SWODY1 SPC AC 201246 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0746 AM CDT Wed Sep 20 2023 Valid 201300Z - 211200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF EASTERN OKLAHOMA...WESTERN ARKANSAS AND NORTHEAST TEXAS... ....SUMMARY... Severe hail and gusts will be possible across parts of eastern Oklahoma, western Arkansas and northeast Texas late this afternoon and evening. ....Synopsis... In mid/upper levels, a strong shortwave trough -- now apparent in moisture-channel imagery over southern BC and northern WA -- is forecast to strengthen to a closed cyclone today and dig south- southeastward. By 00Z, the associated 500-mb low should be near PDT, along a trough extending from northern CA to central/southern AB. By the end of the period, the low aloft will deepen and decelerate over eastern OR, while associated height falls and cyclonic flow spread over most of the CONUS from the Rockies westward. That expansive cyclonic pattern will absorb an initially separate southern-stream cyclone now over the south-central CA coastline. By 12Z, this feature should be a rapidly weakening shortwave trough ejecting northeastward over the Four Corners region. Downstream from these processes, ridging aloft will shift eastward from the southern/central Rockies to the southern/central Great Plains States, with an anticyclonically bent, upper-level, subtropical jet core shifting eastward across NM, the southern High Plains, parts of north TX and OK, and the central Gulf Coast region. To its north, and east of the mid/upper ridge, strongly difluent flow will exist over parts of the central Plains, OK, and the Mississippi Valley. Embedded in that regime, radar and satellite imagery depict a well-defined MCV over southern MO, with shortwave trough southwestward across eastern OK to northeast TX. This feature should move slowly northeastward to eastward, extending from the STL area southward over parts of the Mid-South by 00Z, while a smaller vorticity lobe just upstream blends with the leading perturbation. A subtle shortwave trough now over parts of CO and northern NM will cross the south-central High Plains today, with its weak southern fringes over central OK by 00Z. This trough -- perhaps with some convective vorticity enhancement on the southern end -- should reach eastern KS, southwestern MO, and central AR by 12Z. The 11Z surface analysis showed a wavy, diffuse warm front over the Arklatex region and southern OK, to a low between SPS-CDS, with a slow-moving cold front southwestward from there over southern NM. The low should weaken through the day as lee troughing intensifies farther west across the central/southern High Plains, where a dryline also should settle by early/mid afternoon. The frontal zone east of the low will be reinforced near the Red River today, by outflow and differential heating related to morning clouds/precip. ....OK/AR/northeast TX... Ongoing nonsevere convection and associated cloud cover over eastern OK and northeast TX are expected to shift eastward across southeast OK, AR and parts of northeast TX through early afternoon, in step with the progress of the leading shortwave trough. Although isolated, marginally severe hail cannot be ruled out with this activity, given favorable elevated deep-shear profiles and buoyancy, organized severe potential appears very low. Thunderstorms are possible this afternoon behind that activity, with potential for isolated large hail and strong-severe gusts. However, both spatial and temporal offsets of most-favorable parameters make severe potential marginal and conditional. In a regime of northwest flow aloft and backed near-surface winds in the moist, diurnally destabilizing boundary layer, strong low/middle-level veering with height is expected. Deep shear, and especially cloud-layer shear beneath the north rim of the subtropical jet, will be favorable. However weakening low/middle-level speeds from midday through afternoon will foster shrinking (though still supercell-supporting) hodographs. Low-level shear will strengthen again this evening over the outlook area as a LLJ develops, conterminous with nocturnal cooling/stabilization of the boundary layer. The most heated/ unstable airmass, and weakest MLCINH, may be over southern parts of the outlook area, where any convection that can develop along residual boundaries may move south-southeastward to southward over northeast TX, and into 1000-1500 J/kg MLCAPE. Heating and a narrow corridor of similar or perhaps slightly stronger destabilization are possible near the western rim of the outlook area; however, height rises aloft and capping will limit initiation. This, along with concerns over magnitude and duration of airmass recovery behind ongoing areas of clouds/convection, cast considerable uncertainty on afternoon convective coverage, especially near and north of I-40. Overnight, elevated thunderstorm potential (with isolated hail possible) exists amid steep midlevel lapse rates atop the old outflow plume, across parts of eastern OK and western AR. ...Edwards/Gleason.. 09/20/2023 $$ = = = 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) .