Westby, Montana Weather Forecast Discussion

841
FXUS65 KGGW 301118
AFDGGW
Area Forecast Discussion
National Weather Service Glasgow MT
518 AM MDT Tue Sep 30 2025
.DISCUSSION...
KEY MESSAGES:
- Warm temperatures and dry weather are largely expected through
  today, and then a slow cool down is expected through early next
  week.
- As the ridge breaks down, chances for precipitation begin
  tonight. Weak nocturnal chances remain in place most nights into
  the second half of the week.
WEATHER PATTERN OVERVIEW:
The upper ridge will remain over the northern plains through
today. Precipitation opportunities will start this evening with a
few general showers and maybe a weak thunderstorm or two.
Temperatures will slowly trend downward this week as a trough from
the southwest moves in followed by a trough coming in from the
northwest this weekend.
On Thursday into Thursday night, a shortwave trough will lift
across the region, pushing a stronger cold front and the
possibility of showers through eastern Montana. There remains high
uncertainty in the details of precipitation opportunities beyond
Friday.
FORECAST CONFIDENCE & DEVIATIONS:
Deviations from NBM include a change to hourly PoPs around 06-15Z
tonight as NBM was not fully catching onto the CAMs models axis of
highest rain chances as it passed through the area. Used a
25/25/25/25 blend of SREF NPoP, GFS1HR NPoP, SREF NPoP, and NBM
PPI01. Even then still had to do some minor hand edits to smooth
out deterministic thunderstorm clumps and fill in PoP holes as
the upper level trough axis passed.
There is high confidence of a cooling trend beginning Wednesday
and going through early next week.
There is moderate confidence of precipitation occurring tonight,
and Thursday night.
There is low confidence of precipitation amounts with each
system.
GAH
&&
.AVIATION...
LAST UPDATE: 1115Z
FLIGHT CAT RANGE: VFR
LLWS: Low level wind shear has a chance to impact KSDY and KGDV
early Wedensday morning witha frontal passage. LLWS chances
are expected around roughly 09-13Z.
DISCUSSION: Clear through the morning with mid to high clouds
moving in through the afternoon. A light haze from smoke may
reduce visibility through the cycle, but the impacts should not go
below VFR. Isolated rain showers out west and moving east will
begin impacting the terminals during the mid-late evening and
should exit the area about mid-morning Wednesday. These are
expected to be light and not bring any flight category drops.
WIND: E to SE at 10 kts or less this morning. Veering SE to S and
increasing to 5 to 15 kts this afternoon. Veering farther SW to W
at less than 10 kts this evening through tonight.
EQUIPMENT: At KSDY an AMD NOT SKED will remain in place until the
METARs comms issue is repaired.
GAH
&&
.GGW WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
weather.gov/glasgow

NWS ggw Office Area Forecast Discussion