Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Aug 17 2025 05:52:00 ACUS01 KWNS 170550 SWODY1 SPC AC 170548 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1248 AM CDT Sun Aug 17 2025 Valid 171200Z - 181200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE THIS AFTERNOON INTO TONIGHT ACROSS PARTS OF THE NORTHERN ROCKIES...PORTIONS OF THE MIDDLE MISSOURI VALLEY AND ADJACENT GREAT PLAINS...AND PARTS OF THE NORTHERN MID ATLANTIC... ....SUMMARY... One or two clusters of thunderstorms may develop and gradually pose a risk for strong to severe wind gusts across parts of the northern Rockies into middle Missouri Valley late today into tonight. Strong thunderstorm development accompanied by potentially damaging wind gusts is also possible across parts of the northern Mid Atlantic late this afternoon and evening. ....Discussion... Large-scale mid-level troughing is forecast to undergo further amplification across southeastern Quebec through portions of northern New England and the Canadian Maritimes during this period. As this occurs, a notable cold front is forecast to advance southward across much of the Northeast, Mid Atlantic and Ohio Valley by 12Z Monday, beneath the northeastern periphery of large-scale mid/upper ridging encompassing much of the interior U.S and southern Canadian Provinces. The western flank of the intrusion of cooler/drier boundary layer air is likely to stall across the lower Ohio Valley into Upper Midwest vicinity, but a more modest southward cool surge is also forecast across the northern high plains, in the wake of weak mid-level troughing slowly migrating within the larger-scale ridging across and east of the Dakotas/Nebraska vicinity. A number of other smaller-scale perturbations are forecast to progress through modest/weak cyclonic to anticyclonic flow inland of the Pacific coast through the Rockies, downstream of a significant, amplifying large-scale trough offshore of the British Columbia and Pacific Northwest coast. ....Parts of the mid Missouri Valley into Midwest... Models indicate unsaturated lower/mid-tropospheric thermodynamic profiles with steep lapse rates, aided by continuing eastward advection of elevated mixed-layer air, will be maintained across much of the South Dakota and Nebraska vicinity through this period. Beneath this regime, seasonably high boundary-layer moisture content will continue to contribute to the development of moderate to large potential instability with insolation, along and south of an initially stalled frontal zone across southern Minnesota/southern Iowa through southern South Dakota. Residual convection with a possible MCV may be in the process of spreading well to the cool side of this boundary, across and northeast of the eastern Dakotas at 12Z this morning. There appears at least some potential for renewed convective development along the southern flank of this activity, in closer proximity to the frontal zone and destabilizing boundary-layer (roughly focused near the Minnesota/Iowa border), aided by forcing for ascent associated with warm advection during the day. Otherwise, stronger thunderstorm development may await forcing associated with a perturbation within the southern periphery of the weak mid-level troughing forecast to overspread the (roughly) South Dakota/Nebraska border vicinity by early this evening. There is considerable spread evident among the models concerning these and subsequent developments, with the NAM depicting the evolution of a notable convective perturbation. Other output is less pronounced, but, despite generally weak wind fields and shear, forecast thermodynamic profiles appear potentially conducive to the evolution of an upscale growing and organizing cluster with the potential to produce strong to severe wind gusts this evening and overnight. ....Montana... Downstream of the northeastern Pacific mid-level trough, at least broadly difluent upper flow, perhaps enhanced ahead of a subtle mid-level wave crossing the northern Rockies, may aid the development of thunderstorm activity off the mountains of south central into southeastern Montana late this afternoon and evening. Forecast soundings east of the higher terrain appear to include sufficient shear and favorable thermodynamic profiles for the evolution of a small east-southeastward propagating cluster with potential to produce severe wind and hail. ....Northern Mid Atlantic... Seasonably high moisture content and boundary-layer heating focused along a pre-frontal surface trough may contribute to an environment conducive to a few strong downbursts, aided by heavy precipitation loading. It is possible that forcing for ascent associated with a remnant convectively generated perturbation may contribute to a clustering of thunderstorm activity along this corridor, from parts of northern Virginia through southeastern Pennsylvania and New Jersey, late this afternoon or evening. ...Kerr/Lyons.. 08/17/2025 $$ = = = 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) .