Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Sep 11 2025 05:57:44 ACUS01 KWNS 110557 SWODY1 SPC AC 110555 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1255 AM CDT Thu Sep 11 2025 Valid 111200Z - 121200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM EASTERN MONTANA INTO WESTERN NORTH DAKOTA... ....SUMMARY... A corridor of strong to severe thunderstorms with hail and damaging gusts are expected from eastern Montana into western North Dakota, while isolated/localized wind or marginal hail will be possible across a large portion of the Rockies. ....Synopsis... A large, positive-tilt upper trough will remain nearly stationary across the western CONUS, with axis extending from western NV into southern MB/SK. East of this trough, a broad fetch of 30-40 kt 500 mb southwesterlies will affect much of the Rockies and disturbances rounding the upper ridge into the northern Plains. At the surface, high pressure will maintain stable conditions over much of the East, where a elongated/weak upper trough will exist. Southerly surface winds will maintain a low-level moist plume across the MO Valley with 60s F dewpoints, with 50s F into much of eastern MT where surface winds will back to southeasterly. The combination of daytime heating and substantial southwest flow aloft across a large part of the Rockies, along with at least marginal instability over a wide area suggest sporadic strong to severe storms will be possible during the afternoon and evening. ....Rockies into the northern Plains... Lapse rates will steepen over the area as heating commences, and with the 500 mb -10 C isotherm extending from SD to southern UT. By virtue of an uncapped air mass, sporadic afternoon storms are likely over the higher terrain over northwest NM, CO, and over much of ID into MT, while warm and drier air will generally be found from UT into parts of central WY. However, even in the drier areas, a few storms are likely as weak levels of instability develop. Conditionally, the entire region will have deep-layer shear at or above 35-40 kt, which will favor cellular storm mode. Small hail appears most likely over much of the Intermountain West, with locally strong gusts as well. A potentially greater severe threat will extend from eastern MT and WY into the western Dakotas, where moisture and instability will be greater. A surface low is expected over southeast MT/northwest SD, with backed/moist winds wrapping west. Forecast soundings in this area depict robust CAPE profiles and hodographs favoring cells producing hail, or perhaps bowing structures with both wind and hail risk. Storms may form over south-central MT/northern WY after 21Z, moving into the western Dakotas during the evening. ...Jewell/Wendt.. 09/11/2025 $$ = = = 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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .