Subj : DAY48SVR: Nws Storm Prediction Center Norman Ok To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jul 10 2024 08:52:20 ACUS48 KWNS 100852 SWOD48 SPC AC 100850 Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0350 AM CDT Wed Jul 10 2024 Valid 131200Z - 181200Z ....DISCUSSION... An upper-level ridge will gradually shunt eastward from the southern Rockies into the southern Plains and Lower MS Valley areas this weekend into the middle of next week. Multiple pronounced mid-level shortwave troughs and associated 500 mb speed maxima will pivot around the upper ridge and traverse the Upper MS Valley into the Northeast this weekend through early to mid next week. With adequate low-level moisture and overall instability preceding the mid-level troughs, severe thunderstorms are possible from the Upper MS Valley to the Northeast at least this weekend, possibly into early next week. ....Days 4-5 (Saturday-Sunday) - Upper MS Valley... A 500 mb speed max will traverse the U.S./Canada border on Day 4 (Saturday) as surface lee troughing advects dewpoints well into the 70s F across the northern Plains into the Upper MS Valley. An EML will also precede the mid-level speed max and overspread the rich low-level moisture, contributing to 4000+ J/kg MUCAPE per latest medium-range guidance consensus. Forcing for ascent will be modest and capping will be present, though the approach of the speed max may support convective initiation across the northern Plains into the Great Lakes region. At the moment, too much disagreement exists between medium-range guidance members regarding the placement of convection to support the addition of severe probabilities for Saturday. Despite some timing issues, medium-range guidance is in better agreement in depicting a mid-level impulse and accompanying wave of deep-moist convection traversing the Upper MS Valley area on Day 5 (Sunday). There is some concern that preceding convection from Day 4 could promote stability over portions of the Upper MS Valley into the Great Lakes. Nonetheless, both the ECMWF and GFS agree that the EML will continue regenerate from the southwest, focusing strong to potentially extreme instability into portions of this region. At the moment, it appears the best chance for severe convection (including the possibility of an organized, sustained MCS) would be over central MN into WI Sunday afternoon or evening, warranting the introduction of 15 percent severe probabilities. However, these probabilities may need to be considerably adjusted based on timing/placement changes of key mesoscale features, or to account for any impacts from preceding convection in later outlooks. ....Days 6-8 (Monday-Wednesday) - Northern Plains to the Northeast... The first mid-level impulse will eject into the Northeast on Day 6 (Monday). Some instability will precede this impulse, and medium-range guidance suggests that convective precipitation is possible. However, given limited deep-layer shear and ascent, confidence is too low to provide severe probabilities. Meanwhile, medium-range guidance consensus hints at convective development over parts of the northern Plains toward the Great Lakes on Monday as a second mid-level impulse impinges on the region. Though guidance consensus shows adequate overlapping shear and instability to support severe storms, relatively weak forcing for ascent and convective signals in the guidance preclude severe probabilities. By Days 7-8 (Tuesday-Wednesday), the second approaching mid-level trough will amplify while overspreading the Great Lakes, supporting a southward-surging cold front from the MS Valley into the northeast. Forcing for ascent and accompanying buoyancy suggests severe thunderstorms are possible from the MS Valley to New England. However, details on frontal timing and placement this far in advance are too nebulous for severe probabilities at this time. ...Squitieri.. 07/10/2024 = = = 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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .