Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jun 24 2023 12:56:34 ACUS01 KWNS 241256 SWODY1 SPC AC 241255 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0755 AM CDT Sat Jun 24 2023 Valid 241300Z - 251200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF IOWA AND MINNESOTA INTO THE MID MISSISSIPPI VALLEY... ....SUMMARY... Severe thunderstorms, associated with wind damage, large hail and perhaps a couple of tornadoes, will be possible from parts of Iowa and Minnesota into the mid Mississippi Valley this afternoon and evening. ....Synopsis... Although the mean/large-scale ridge position aloft still extends from the northern MX high across the central Plains to ON, it will be penetrated today by a compact cyclone now evident in moisture- channel imagery over the northern High Plains. The 500-mb low is forecast to move erratically eastward to near the MN Twin Cities region by the end of the period, with shortwave trough to northeastern KS. Today, strongly difluent mid/upper flow will spread across the mid/upper Mississippi Valley to its east and southeast. A longstanding, gradually weakening upper trough over the eastern CONUS will shift slowly eastward toward the East Coast. At the surface, 11Z analysis showed a low over east-central SD near HON, with cold front across south-central NE to northwestern KS and southeastern CO. The low will closely follow the mid/upper vortex center track, while occluding. The cold front should reach western IA, northeastern KS and southeastern CO by 00Z. By 12Z tomorrow, the cold/occluded front will reach eastern parts of IA/MO as well as southwestern MO, southwestern OK and eastern NM. A warm front was drawn over the lower Missouri Valley, and should move/redevelop northeastward across the mid/upper Mississippi Valley through the period ahead of the low. ....Mid/upper Mississippi Valley region... Scattered thunderstorms may develop this afternoon between the northern Red River Valley near the deep-layer low, and the mid Mississippi Valley region. The greatest severe threat still appears to be over parts of IA, MO and IL, though a good deal of it remains conditional. Tornadoes, along with large to very large hail and locally severe gusts, are possible. An ongoing, slowly weakening, mostly non-severe thunderstorm complex across southwestern MN to northern/western IA will exert substantial influence on later severe-weather potential across the same region and nearby mesoscale areas. The northern part is expected to continue moving into a lower-theta-e environment over MN, WI and northern IA. Meanwhile, the southern part should shift eastward/ southeastward across IA, with some afternoon rejuvenation possible along the associated pressure perturbation and UVV plume. The more probable scenario is for a new round of severe thunderstorms to form in its wake as warm/moist advection occur from the south and southwest, and diurnal heating destabilizes the boundary layer following departure of substantial associated cloud cover. Surface dewpoints in the 60s and perhaps near 70 F, and a few hours of heating, should support peak, prefrontal/preconvective MLCAPE in the 2000-3000 J/kg range. This area also will reside in a regime of deep large-scale ascent -- overlying the warm advection with midlevel DCVA and lift beneath the left-exit region of 250-300-mb jet. Sufficient flow aloft will exist for 35-45-kt effective-shear magnitudes, with a pocket of large low-level hodographs and SRH potentially developing over central/northern IA or southern MN. With the bulk of the morning MCS still over or west of the possible area of interest, there still is considerable uncertainty on where the optimal mesoscale pseudo- warm-frontal transition zone may set up in the wake of the complex. A focused area of enhanced supercell/tornado and large-hail potential may develop on any such boundary, with lower buoyancy, backed flow and high SRH to its northeast, and greater heating/CAPE but still adequate low-level shear to its southwest. If a dominant supercell or two can occur in this environment prior to upscale growth (not yet a given), greater tornado probabilities and perhaps significant-tornado area may be needed. Farther north across portions of central/northern MN, boundary-layer instability will be weaker this afternoon. However, a narrow plume of favorable, effectively surface-based parcels may develop east and southeast of the deep-layer low, supporting an arc of convection that may include low-topped supercells. Given uncertainties regarding airmass recovery, with considerable cloud cover likely over the area for most of the day, unconditional tornado potential remains marginal, but the most-aggressive destabilization scenarios support the potential for a few in that area. ....Southwest to north TX... Isolated to widely scattered, high-based thunderstorms are expected to develop along/ahead of a dryline drawn this morning over eastern NM and far west TX, but expected to mix rapidly eastward across west TX today, amidst seasonally intense diurnal heating. Activity will originate atop a very deep/well-mixed boundary layer with dry- adiabatic lapse rates (superadiabatic very near surface), with moisture content increasing and surface temperatures decreasing northeastward. Strong/isolated severe downbursts will be possible over the entire outlook area, and enough inflow-layer moisture to support isolated large hail is possible over northwest TX and perhaps parts of the Big Country. ...Edwards/Mosier.. 06/24/2023 $$ = = = 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) .