Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue May 30 2023 12:46:52 ACUS01 KWNS 301246 SWODY1 SPC AC 301245 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0745 AM CDT Tue May 30 2023 Valid 301300Z - 311200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE CENTRAL HIGH PLAINS... ....SUMMARY... Severe thunderstorm gusts -- some reaching at least 75 mph -- are possible from this afternoon into early evening over portions of the central High Plains. ....Synopsis... A slowly evolving, largely shortwave-dominant pattern will prevail in mid/upper levels, with mean troughing lingering over the Gulf of Mexico and just off the Pacific Coast of the U.S. and Canada. One such shortwave perturbation -- apparent this morning over central ND -- is forecast to shift east-northeastward over northwestern MN by 00Z, then weaken as it ejects over westernmost areas of northern ON. A compact cyclone aloft -- now centered offshore from south-central CA -- should cross much of southern CA through the period. Between these features, assorted existing and future convectively aided/ induced vorticity maxima should exert greatest convective influence above the surface, though a weak shortwave perturbation is evident in moisture-channel imagery over southwestern CO and north-central/ northwestern NM. At the surface, 11Z analysis showed weak pressure gradients and a rather chaotic, nebulous pattern east of the Rockies, save for a dryline drawn from the western Dakotas southward over eastern CO, extreme eastern NM and far west TX. This dryline should mix eastward somewhat today, but not very far, in the absence of substantial mid/upper forcing. ....Central High Plains... Scattered thunderstorms are expected to develop this afternoon in a loosely north-south swath over and either side of the eastern sections of the Palmer and Cheyenne Ridges, where surface heating on, and mixing over, relatively high terrain will erode MLCINH soonest. This activity should be high-based for much of its lifespan, with large dewpoint depressions in its inflow region over eastern CO, western KS and western/southwestern NE near the dryline. The main concern will be severe gusts, with some significant-severe gusts possible given likely upscale organization of activity and a deep, well-mixed boundary layer. Diurnal heating will contribute to mean surface-500-mb lapse rates commonly near 9 deg C/km, supporting peak/preconvective MLCAPE to near 2000 J/kg, even with dewpoints mixing into the 40s to low 50s ahead of the convection. The apparent peak in both density and intensity of wind potential appears to be near the CO/KS line and a few counties into western KS. This corridor appears most likely for convection that has had a chance to aggregate an optimally organized outflow/cold-pool process and move into a strongly/deeply mixed boundary layer with large DCAPE, but before it moves too far east into a nocturnally stabilizing low-level regime and outflow substantially outruns convection. Mesoscale uncertainties preclude an unconditional upgrade to the wind outlook this cycle, but one may be needed after evaluation of 12Z guidance and further observational trends. ....Missouri Valley to upper Mississippi Valley... Widely scattered to scattered, predominantly multicellular thunderstorms are expected to develop beginning midday into mid- afternoon across parts of the lower Missouri Valley region of IA/NE/MO and northeasternmost KS. Locally damaging to marginally severe gusts and hail are possible before convection weakens this evening. The activity should form in an arc of mesoscale spatiotemporal enhancements to deep-layer lift, overlapping upper 50s to low 60s F surface dewpoints and diurnally boosted MLCAPE in the 1500-2000 J/kg range. The strongest UVV arc should be situated generally northeast through south of an MCV from prior evening/ overnight activity over the central High Plains. The MCV was evident in composited radar imagery over southern NE near the KS border, between HSI-BIE, and should move roughly eastward toward the FNB area through the day. Despite some potential enhancement to midlevel flow, overall low-level and deep-layer shear should be weak. Farther north, a similar plume of large-scale ascent should cross a surface trough over parts of MN and perhaps the Soiuxland area today, ahead of the mid/upper-level shortwave trough. Isolated to scattered thunderstorms may develop from a weakly capped boundary layer, offering sporadic hail -- some of which may reach severe limits. Convective organization should be aided by a channel of gradient-enhanced mid/upper southwesterlies east and southeast of the trough aloft. Forecast soundings suggest around 1500-2500 J/kg MLCAPE and weak low/middle-level winds veering with height. However, weak low-level shear and effective shear also are expected. ...Edwards/Jewell.. 05/30/2023 $$ = = = 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) .