Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jun 28 2023 19:59:55 ACUS01 KWNS 281959 SWODY1 SPC AC 281958 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0258 PM CDT Wed Jun 28 2023 Valid 282000Z - 291200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE NORTHERN HIGH PLAINS...AND UPPER MISSISSIPPI VALLEY... ....SUMMARY... Large hail, isolated damaging winds and a tornado or two are possible this afternoon/evening across northwest Wisconsin/eastern Minnesota as well as the central High Plains including southeast Wyoming and western Nebraska. Minor expansion of the Slight Risk over SD/NE at 20Z. Storms are just forming over the northern High Plains, and a severe thunderstorm watch has been issued. For more information see mesoscale discussion 1319. Additional severe storms remain possible later today from near the Twin Cities into western WI. The air mass continues to destabilize with gradual moisture advection from the south/southwest. ...Jewell.. 06/28/2023 ..PREV DISCUSSION... /ISSUED 1152 AM CDT Wed Jun 28 2023/ ....Upper Mississippi Valley this afternoon through late evening... No outlook/forecast reasoning changes appear warranted. A shortwave trough (enhanced some by prior convection) will progress eastward over Minnesota/Wisconsin through evening. An associated/weak surface cold front will likewise move eastward across Minnesota, while low-level moistening occurs from the southwest during the day beneath a lingering plume of steep midlevel lapse rates. MLCAPE will increase to 2500-3000 J/kg with sufficiently long/curved hodographs for a supercell threat later this afternoon/evening from eastern Minnesota into northwest/western Wisconsin, along and just ahead of the front. Large hail will be the main threat, though isolated wind damage and a tornado or two will also be possible. ....Central High Plains this afternoon and tonight... Low-level flow will veer to easterly during the afternoon, with boundary-layer dewpoints from the mid 50s to lower 60s F in the upslope regime. Subtle speed maxima aloft and surface heating in cloud breaks should allow weakening of convective inhibition by mid-late afternoon, when at least isolated thunderstorm development is possible from eastern Wyoming into the Nebraska Panhandle, and possibly northeast Colorado and/or the South Dakota Black Hills vicinity. Moderate buoyancy and long, relatively straight hodographs will favor supercells capable of producing isolated very large hail, along with some potential for strong-severe outflow gusts and a tornado or two. A semi-organized cluster or two could evolve and progress east-southeastward this evening toward/across west/southwest Nebraska. ....Northern/central Illinois and eastern Iowa... The potential for deep convective development, and uncertain timing thereof, remains a key uncertainty for parts of Iowa/northwest Illinois. There appears to be a conditional potential for surface-based development late this afternoon/early evening in vicinity of the warm front and/or surface trough across west/central into southern Iowa. Strong deep-layer wind profiles, very steep mid-level lapse rates and ample buoyancy would support severe storms/supercells, although the degree of capping leads to uncertainty regarding the likelihood/extent of convective development around peak heating. Convective development will be more probable tonight as warm advection increases related to the strengthening of a west-southwesterly low-level jet. The chance for elevated thunderstorm development will increase overnight from eastern Iowa into Illinois. MUCAPE >2500 J/kg, steep mid-level lapse rates and effective bulk shear >50 kt will support the potential for elevated supercells to produce large hail, while DCAPE >1000 J/kg suggest some potential for strong gusts to reach the ground. There still remains substantial uncertainty regarding the specific corridor and timing of storm development late this afternoon into, so will continue to maintain the Marginal risk at this time. $$ = = = 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) .