932
FXUS65 KMSO 161037
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
337 AM MST Sun Nov 16 2025

.DISCUSSION...

After a persistently mild November, all indications point to a
major and abrupt pattern change arriving for the Thanksgiving
holiday week. This will be a significant "shock to the system" and
likely the first widespread, low-elevation winter impact of the
season. Residents should use the relative calm of the upcoming
week to finalize all winter preparations for homes and vehicles,
especially ahead of the busy travel period.

KEY MESSAGES:

-  Periodic light mountain snow through Wednesday with minimal
   impacts.

-  Significant pattern change next weekend (Nov 22-23) with a
   potential atmospheric river bringing heavy mountain
   precipitation.

-  High confidence in a colder, wintry pattern for Thanksgiving
   week, including valley snowfall.


Short-Term: Through Wednesday

A split-flow pattern will persist through midweek, deflecting the
main storm track. We`ll see two weak waves of moisture:
1) Today through Monday: Light showers, mainly for central Idaho
and northwest Montana. Snow levels around 7,000 feet. Minimal
impacts with a trace to 2 inches on the highest passes.

2) Tuesday-Wednesday: A second, slightly cooler system. Snow
levels drop to 4,500-5,000 feet. Impacts: Minor accumulations
(generally 1 inch or less). Roads should remain in good condition
during the day, with any slick spots confined to passes overnight.

Mid-Term: The Weekend Pattern Change (Nov 22-23)
Confidence is increasing for a major pattern change as an
atmospheric river (AR) takes aim at the Pacific Northwest. This
system is supported by a very strong 130+ kt upper-level jet,
placing our region in the favorable left-exit region for heavy
precipitation.

- Heavy Precipitation: The potential for heavy mountain
  precipitation is high. The NBM 4.3 90th percentile shows 1.00"
  24-hour total precipitation (ending 5 PM Sat), with the ECMWF
  Ensemble 90th percentile showing 1-2 inches of liquid in the
  same timeframe for the mountains along the ID/MT border.

- Snow Level Uncertainty: This is the key forecast challenge. The
  position and track of the AR is critical. Milder Solution: A
  slight northward shift would keep this a milder, higher-
  elevation snow event. Colder Solution: A more southerly track,
  as hinted at by some ensemble members, would be more impactful.
  The NBM 4.3 10th percentile snow levels are near 2900 ft for
  Saturday across northwest Montana. This scenario could bring
  accumulating wet snow to valley locations.

Long-Term: Thanksgiving Week
This is the period of highest potential impact. The evolution
gets fuzzy, but instead of a quick frontal passage, models suggest
one of the coldest upper-level troughs of the season could dig
over the West Coast.

Temperatures: Confidence is high in a transition to a very cold,
wintry pattern. The NBM 4.3 shows a 50-60% probability that highs
will remain below freezing on Tuesday across western Montana
valleys.Those probabilities increase to 70-80% by Wednesday. NBM
probabilities for lows below 17 degrees Fahrenheit increase
significantly by Tuesday morning along the Divide and expand to
include all western Montana valleys by Wednesday morning. Sub-zero
lows are possible later in the week along the Divide.

Snow: This pattern is very favorable for low-elevation snow.
While specific amounts are highly uncertain, the pattern itself is
concerning. Looking at ensemble probabilities, the synoptic setup
could be conducive for a surface low to track from southern Idaho
towards southwest Montana. This is a good pattern for valley
snowfall, north and west of the low`s track. If the west coast trough
digs too much, then we could be milder with less precipitation...but
a caveat, if a trough digs more, then it could draw Arctic air
out of Canada and bring colder temperatures sooner (we`re talking
Monday/Tuesday).

The cold air brought in by the trough, combined with an active
northwest flow and unstable atmosphere, could lead to ongoing,
convective snow showers and persistent slick conditions on area
passes and valley roads.


&&

.AVIATION...A shortwave will bring light showers and clouds from
south to north today. Highest confidence for showers across
north-central Idaho through 16/1800Z or 1000 PST, and then across
northwest Montana this afternoon through tonight. Patchy fog
and/or stratus is possible this morning and also Monday morning.
Occasional mountain obscurations may occur today but more
impactful reduced ceilings generally wait until tonight/Monday
morning. Winds will be relatively light into Monday with the
highest gusts only reaching 15-20 kts and confined to southwest
Montana/Lemhi County each afternoon.


&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&

$$