Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jul 11 2023 20:02:13 ACUS01 KWNS 112002 SWODY1 SPC AC 112000 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0300 PM CDT Tue Jul 11 2023 Valid 112000Z - 121200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE NORTHERN/CENTRAL PLAINS INTO THE MIDWEST... ....SUMMARY... Supercells capable of large to very large hail are possible this afternoon and evening from eastern Montana and western South Dakota into Nebraska. One or more convective lines may evolve late this evening and overnight from central Nebraska into Iowa. Severe wind gusts may occur with this convection. ....20Z Update... The Slight Risk area has been expanded to include more of northeastern MT, western ND, and northwestern SD. Multiple supercells capable of producing large to very large hail should spread east-southeastward across this area through the rest of the afternoon and evening. See Mesoscale Discussion 1498 for more details on the short-term severe threat across this region. Otherwise, minimal changes have been made to the ongoing forecast. Additional convection should eventually develop across parts of NE along/near a front as low-level warm advection gradually increases later this evening. This activity may initially pose a threat for large hail. But, quick upscale growth into an MCS should occur, with a greater threat for severe/damaging winds through the overnight hours across eastern NE into IA. Reference Mesoscale Discussion 1499 for additional information regarding thunderstorms which have recently developed across parts of northern IL and far northwestern IN along a weak front. Isolated strong to severe wind gusts should be the main threat with this activity. ...Gleason.. 07/11/2023 ..PREV DISCUSSION... /ISSUED 1130 AM CDT Tue Jul 11 2023/ ....Eastern MT into SD/NE... Early morning surface analysis places a lee trough across eastern MT to weak low over the northwest NE. Airmass in the vicinity of the lee trough is currently characterized by mid 50s to low 60s dewpoints. Modest mid-level warm advection is fostering widespread cloud cover to the east of the lee troughing across far eastern MT and the Dakotas. This area of cloud cover is forecast to shift eastward over time, allowing for daytime heating to destabilize the air mass. Low-level convergence along the lee trough will be augmented by increasing large-scale forcing as the shortwave trough currently over western MT moves eastward into the region. This combination of air mass destabilization and forcing for ascent is expected to foster thunderstorm development across western MT during the afternoon. Low 60s afternoon dewpoints and temperatures in the 80s beneath steep mid-level lapse rates will support moderate to strong buoyancy, with MLCAPE from 1500 to 2500 J/kg. Enhanced mid-level flow will extend across the region as well, supporting long hodographs and 50+ kt of 0-6 km vertical shear. These environmental conditions will result in an initially supercellular mode, with large to very large hail possible for both left and right splits. High cloud bases suggest strong downbursts are possible as well. Evolution into one or more bowing segments is anticipated after a few hours, with these segments progressing eastward into southwest ND and western SD during the evening, and eventually into parts of NE. Severe threat will continue with these bowing segments, with damaging gusts as the primary risk. ....Central SD/NE into IA... Early morning surface analysis places a cold front from southern IA westward across central NE, linking up with lee troughing across eastern MT via a weak low over the northwest NE Panhandle. Elevated showers and thunderstorm are currently ongoing north of the front across central SD and central NE, with outflow from these storms now emerging across north-central NE. A trend towards more surface-based activity is possible as this outflow continues southward/southeastward as well as with the more southerly storm across central NE. There is also the chance for more in-situ development along the front later this afternoon if skies clear. Main uncertainty is whether or not the air mass sufficiently destabilizes given the current cloudiness and relatively warm mid-levels. As such, a conditional threat for severe thunderstorm is anticipated throughout the afternoon and into the evening, with strong shear likely supporting supercells capable of large to very large hail and damaging gusts. Later this evening, whatever evolves out of the upstream activity across eastern MT and NE Panhandle will likely progress into the region, supporting the potential for damaging gusts and isolated hail throughout the night. Some significant gusts are possible, depending on how organized the system is as it moves into central NE. Even at this shorter range, guidance remains varied on the preferred corridor for this potential MCS, limiting the confidence needed to introduce higher wind probabilities with this outlook. ....North TX into southern MS/AL... MCS that moved across OK last night has weakened considerably, but a well-developed MCV in it wake. This MCV is forecast to drift southeastward throughout the day, with thunderstorms likely in its vicinity as well as along the leading edge of the southeastward-progressing outflow. Winds aloft are weak, which should keep the overall severity limited, with a risk of locally damaging wind gusts in the stronger cells. $$ = = = 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) .