500
FXUS65 KGGW 300454
AFDGGW

Area Forecast Discussion
National Weather Service Glasgow MT
1054 PM MDT Tue Sep 29 2026

.KEY MESSAGES...
- A weak cool front will move through the area this morning
  allowing sliughtly cooler but dry conditions today.

- The first major frost of the season is possible in some
  locations along valley bottoms Thursday and Friday morning.

- There are small chances for isolated stratiform showers Thursday
  morning through Friday night. Rain totals will be minimal.


&&

.DISCUSSION...
Synoptic Setup: Forecast begins with zonal flow running from off
the coast of the Pacific Northwest through the PCNW and Montana.
North of this is cooler air at the surface embedded in a broad
trough over the southwestern quadrant of Canada that is leaking
down into the Plains and northeast Montana. To the south a large
closed low sits over the Four Corners with a ridge just west of it
running north from the Baja and cresting over northern
California.

Today: The zonal flow jet stream will drag pacific moisture in
the mid and high levels across the region generatng clouds today
which could reach near broken to overcast status at high levels.
The ceilometers across the region can not measure above 12kft and
are reporting SKC which is leading to a strong feedback effect
with no clouds in the current model data. Meanwhile, the ridge
over Cali will begin expanding and widen into the Intermountain
west bumping up against the zonal flow to the north.

Tonight into Friday: The jet stream near the US/Canadian border
will go from a zonal position to more of a W-NW orientation as the
ridge to the south presses on it. A subtle shortwave at the mid
levels is expected to move through this flow and could kick off a
few stratiform showers Thursday and Friday. Temps will be quite
cool Thursday with surface high pressure in place and should be
the coolest day in this forecast period. Thursday night into
Friday morning could experience some frost on over valley bottoms
if skies manage to clear out enough.

Saturday into Monday: Surface high pressure over the Canadian
prairies looks to be in place this weekend with flow becoming full
NW. This will keep daytime temps slightly below normal and lead
to dry conditions due to now very limited Pacific moisture.

Monday night onward: Ensemble breakdown begins to occur as the
northwest flow gets interrupted by the ridge to the southwest.
The placement and strength of this ridge axis looks to be in
flux. Therefore, forecast confidence drops off here onward.

FORECAST CONFIDENCE & DEVIATIONS:
Deviations to NBM include... Sky grids for the first 18 hours
which used a 50/50 blend of NBM/CONSMOS. Effectively ceilometers
are registering nothing below 12kft but Satellite is showing near
BKN to OVC skies in some locations well above this height. The
ceilometers are having a feedback effect of removing clouds on
model data which is then producing outrageously low or incorrect Sky
values in the NBM ensemble output.

GAH


&&

.AVIATION...
LAST UPDATED: 0450Z

FLIGHT CAT RANGE: VFR

DISCUSSION: High clouds will lower into the CWA Wednesday morning
and afternoon before gradually lifting by the evening hours.

WIND: Surface winds will increase in the afternoon with gusty
conditions returning in the afternoon. Winds should become
generally light and variable in the evening.

KENZ


&&

.GGW WATCHES/WARNINGS/ADVISORIES...
None.


&&

$$

weather.gov/glasgow