Subj : DAY48SVR: Nws Storm Prediction Center Norman Ok To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue May 13 2025 08:59:50 ACUS48 KWNS 130859 SWOD48 SPC AC 130858 Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0358 AM CDT Tue May 13 2025 Valid 161200Z - 211200Z ....DISCUSSION... An active period of severe weather is anticipated through early next week as a pair of upper-level troughs traverse the U.S. and will be favorably timed to allow moisture recovery into central/southern portions of the CONUS. The upper trough currently over the Pacific Northwest is forecast to migrate into the Great Lakes region by this weekend. In the wake of this feature, a second long-wave trough will begin to deepen across the West before migrating into the Plains by early/mid next week with attendant chances for strong/severe thunderstorms. ....D4/Friday... A stalled boundary will likely be draped from the Ozarks into the OH Valley at the beginning of the forecast period. A weak, low-amplitude mid-level perturbation emanating out of the central Plains will promote secondary surface low development across the southern Plains that will maintain southerly low-level flow. As such, some northward migration of the boundary as an effective warm front appears probable. Thunderstorm development along the boundary is anticipated by late afternoon, and 40-50 knot mid-level flow oriented along the frontal zone should promote initially discrete/semi-discrete cells with the potential for upscale growth into one or more organized clusters. Some disagreement in exactly where the corridor of highest severe threat will become established persists and is associated with the coverage and intensity of ongoing convection Friday morning. Recent GFS/GEFS runs hint that more isolated convection early Friday will allow for more aggressive northward advancement of the front, while ECMWF solutions hint at slower northward progression of the boundary. The 15% risk area has been expanded to best encompass the overlap between these two dichotomous solutions. ....D6/Sunday to D8/Tuesday... A deepening upper level trough over the western states will promote several days of lee troughing/cyclogenesis across the southern to central High Plains beginning this weekend. This will allow for more seasonal moisture return into the Plains with most ensemble members showing dewpoints climbing into the low to mid 60s by D6/Sunday afternoon across TX, OK, and southern KS. Deterministic solutions continue to vary regarding the exact timing and evolution of the upper-level wave (and any embedded impulses), but the general consensus is that severe thunderstorms will be possible as upper-level disturbances overspread the Plains and promote eastward mixing of the dryline into an increasingly buoyant warm sector. Confidence on any particular day remains too limited for risk probabilities, but the overall synoptic regime and convective QPF signals in ensemble guidance suggest that the potential for multiple rounds of severe thunderstorms is increasing for the southern/central Plains beginning D6/Sunday through D8/Tuesday. ...Moore.. 05/13/2025 = = = 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) .