562
FXUS65 KGGW 211004
AFDGGW

Area Forecast Discussion
National Weather Service Glasgow MT
304 AM MST Fri Feb 21 2025

.DISCUSSION...

KEY MESSAGES:
- Arctic cold will continue shallowing out of the area this week
  with each day warming about 10 degrees into the weekend.

- Some light rainfall is possible Sunday night to Monday night any
  rain that does far will likely freeze on frozen ground leaving
  icy roads and sidewalks.

- Thawing conditions will lead to difficult access on unpaved
  roads, mud during the daytime, this weekend into early next
  week.


WEATHER PATTERN OVERVIEW:
Surface high pressure over the central Plains and strengthening
jet stream over western Canada will continue arctic air`s
eroding/shallowing this afternoon. The warm air has moved in at
mid-levels over northeast Montana but low-level southeasterly
winds have kept temps much cooler under the inversion where snow
pack remains in place.

The winds should gradually turn west and allow the warmer
chinooked air to move in late this morning. But will hold back
rises in temps along some of the valleys such as the Milk and
Missouri river till Saturday as cooling at night and lack of
mixing and remaining snowpack will redevelop the inversion after
dark. Fog is very likely (40-60% chance)(03-16Z) to set up in
these river valleys as excess moisture from snowmelt out west will
settle in under the inversion and be chilled rapidly by leftover
snowpack on valley bottoms.

Sunday onward, ensembles increase west winds strongly and this
should erode any remnants of the boundary layer and begin eating
snowpack in Valley bottoms as well. Some chances(10-30%) for light
rainfall (<0.02") could make things icy with the frozen ground
especially at night. No concrete idea when this will occur but
things will have to be watched for possible highlights. Otherwise,
mud is a possibility each day as ground thaws. TFJ/GAH


FORECAST CONFIDENCE & DEVIATIONS:
Deviations include 50/50 of NBM/NBM10 for today and tonights
highs and lows. 50/50 NBM/NBM25 for Saturday and Saturday night
highs and lows. Addition of Fog along the Milk and Missouri
Valleys Saturday morning. And 50/50 NBM/NBM90 for wind Saturday
from 15-03Z.

Ensembles continue to skew down rain chances and totals (barely
0.02") for rain early next week. Went with NBM for now but we may
have to go above NBM when we get more confidence (as impacts
could be significant if icy conditions develop). TFJ/GAH


&&

.AVIATION...

LAST UPDATED: 0900Z

FLIGHT CAT RANGE: VFR - IFR

DISCUSSION: Mainly clear skies are expected through tonight but
there is a slight chance (5-10%) of IFR fog development at KGGW-
KOLF through 11-16z Friday. IFR fog will have a much greater
chance (40-60%) Saturday morning from at these same sites from
03-15Z.

WIND: W to SW or Variable and light through this morning.
Increasing to 5 to 15 kts this afternoon through tonight. Then
Veering to W and increasing to 10 to 20 kts Mid Saturday morning.

LLWS: Low level wind shear is expected to impact the terminals
periodically tonight from 06-15Z.

GAH


&&

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

$$

weather.gov/glasgow