Area Forecast Discussion
Issued by NWS Glasgow, MT
Issued by NWS Glasgow, MT
371 FXUS65 KGGW 211952 AFDGGW Area Forecast Discussion National Weather Service Glasgow MT 152 PM MDT Mon Sep 21 2026 .KEY MESSAGES... - Potential rain showers and thunderstorms (to a much lesser extent) in areas SE of the Missouri river between early morning and mid-afternoon Wednesday. - Wind and precipitation forecasts for Friday and Saturday will continue to be monitored closely. Precipitation chances are currently uncertain and winds speeds are expected to be higher than current model guidance suggests. && .DISCUSSION... SYNOPTIC SETUP: The low pressure system that brought rain to Montana this past weekend is exiting eastward ahead of an upper-level ridge building over the state. The developing ridge will result in cloud ceilings scattering out and skies becoming fair by this evening. The ridge will remain anchored over the northern Great Plains region through tomorrow afternoon, producing southwesterly flow aloft and subsequent warmer temperatures across NE Montana. A shortwave trough will move across northern Wyoming and eastern Montana tomorrow night into Wednesday morning. Low-level moisture and instability associated with the trough could potentially induce rain showers and thunderstorms (to a much lesser extent) in areas SE of the Missouri river between early morning and mid- afternoon Wednesday. Isolated thunderstorms will likely be limited to regions SE of the Yellowstone River. Thursday and Friday will have widespread afternoon temperatures in the low to mid 80s as ridging resumes following the passage of the shortwave trough. Highest temperatures of the week trend warmer on Thursday as of current model runs, suggesting a quick exit of the ridge Friday evening ahead of an approaching upper- level trough. Although timing discrepancies are currently present between the GFS and ECMWF, the trough is expected to begin digging over eastern Montana between Friday evening and Saturday afternoon. Vorticity advection is particularly significant ahead of this trough according to current model guidance. However, the vast majority of present low-level moisture is indicated to track north, potentially resulting in an absence of widespread precipitation. As model guidance develops, forecasted precipitation could change. FORECAST CONFIDENCE & DEVIATIONS: Winds Friday night and Saturday associated with the upper-level trough will need to be monitored, as the NBM/GFS/ECMWF could potentially be washing higher speeds out. Strong frontogenesis from sinking air on the cold side of the low is trending stronger, meaning this event will need to be watched for wind headlines. DON && .AVIATION... LAST UPDATED: 1850Z FLIGHT CAT RANGE: MVFR/IFR -> VFR -> IFR DISCUSSION: MVFR/IFR ceilings will persist through the morning, potentially into the early afternoon, before rising and scattering out by mid-afternoon. Ceilings will redevelop and lower tomorrow morning, becoming IFR across the board by 12Z. WINDS: SE at 08 to 14 kt with gusts to 20 kt this afternoon and evening. Gusts of up to 24 kt possible tomorrow morning at KSDY. && .GGW WATCHES/WARNINGS/ADVISORIES... None. && $$ weather.gov/glasgow