Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jun 18 2023 12:36:19 ACUS01 KWNS 181236 SWODY1 SPC AC 181234 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0734 AM CDT Sun Jun 18 2023 Valid 181300Z - 191200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE LOWER MISSISSIPPI VALLEY REGION TO THE EAST-CENTRAL GULF COAST... ....SUMMARY... The main severe-thunderstorm potential will be in two phases -- damaging wind and isolated large hail this morning and again this afternoon into tonight -- from the lower Mississippi Valley region to the east-central Gulf Coast. ....Synopsis... In mid/upper levels, a rather chaotic pattern will be in place, downstream from and southeast of a pronounced, positively tilted cyclone with slow net east-southeastward motion over the Northwest States. Ridging will build ahead of this feature, from the southern Rockies across the central/northern Plains. Farther east, a pronounced, convectively augmented shortwave trough is apparent in satellite imagery over eastern portions of KS/OK, with pronounced MCV/cyclone center over southeastern KS. A weaker and more recent MCV precedes this trough, and was located over the MEM region. A 500-mb cyclone -- incorporating the MCVs and perhaps lesser vorticity maxima -- will shift eastward across the Ozarks to the lower Ohio Valley through the period. At the surface, 11Z analysis showed an outflow boundary from western Tn to near the MS/AL line around MEI (astride a warm front in this region) then southwestward across northern LA to northeast TX. This boundary will move northeastward over the lower Mississippi Valley today and become somewhat more diffuse. The warm front extends from the MEI area southeastward across the MOB/PNS area and into the northeastern Gulf, and should move slowly northward where not intercepted by active outflow. A cold front across parts of north- central, west-central and far west TX will move southeastward through the period, while an attached low now over north-central TX moves eastward to the Arklatex region, and a new low develops overnight over the lower Ohio Valley (ahead of the mid/upper perturbation). ....Mississippi Delta/Gulf Coast States... Probabilities driving the "enhanced" categorical area reflect a cumulative effect of multiple rounds of convection through the period. Ongoing clusters of strong-severe thunderstorms are noted in an arc from western TN across western AL to southern MS, with the best-organized and longest-lived threat this morning being on the southern end where foregoing moisture/instability is greatest. Isolated damaging gusts and marginally severe hail may occur elsewhere in the arc as it moves generally into more stable conditions, as well as with a couple clusters of trailing convection located over the outflow pool (but still accessing unstable inflow above the surface via the remaining southwesterly LLJ). Refer to Severe Thunderstorm Watches 332 and 333, and related mesoscale discussions, for near-term guidance on that activity, and Mesoscale Discussion 1148 for trailing convection atop the outflow pool in the Arklatex region. As the southern/western part of the outflow boundary related to the morning activity modifies, becomes shallower, and retreats northeastward as an effective warm front through the afternoon, the very moist airmass south of and within the associated baroclinic zone will become increasingly unstable via diurnal heating and warm advection. Another round of scattered to numerous thunderstorms is expected to develop in the Arklatex region, northeastward along a plume of relatively maximized large-scale ascent just ahead of the shortwave trough, and low-level convergence near a weak surface low. Activity should move roughly southeastward this evening, into a recovering airmass with a 40-50-kt southwesterly LLJ. Considerable uncertainty remains on the extent of this development, especially on the poleward end farthest from the remnant boundary. Still, a northeastward-spreading plume of 2000-3500 J/kg MLCAPE may linger well into the evening and into the convective inflow region, supporting an increasing threat for severe gusts. Scattered large to very large hail also is possible, especially with relatively discrete development in early stages, and with any trailing convection that forms over outflow. ....Eastern MT... Widely scattered, high-based, multicellular thunderstorms should develop this afternoon along/near the cold front, as the frontal zone impinges on a diurnally destabilizing and well-mixed boundary layer this afternoon. Isolated severe gusts may occur. Despite modest surface dewpoints (generally mid 40s to lower 50s F after mixing), sufficient low-level moisture will remain to support warm-sector MLCAPE around 200-500 J/kg, atop steep lapse rates in the subcloud layer, roughly surface-700-mb. Nearly unidirectional deep-tropospheric flow is forecast, limiting bulk shear and overall storm organization. ...Edwards/Jewell.. 06/18/2023 $$ = = = 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) .