Lewistown, Montana 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

492
FXUS65 KTFX 222349
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
449 PM MST Mon Dec 22 2025

Aviation Section Updated.

.KEY MESSAGES...

- Periods of mountain snow and some scattered areas of lower elevation
  light rain, snow, or mixed precipitation continue for much of
  the week.

- Strong and gusty southerly winds develop over Southwest Montana
  late Tuesday night and persist through Wednesday night, most
  notably in the Madison River Valley.

- Near to above average temperatures are expected for most
  locations, but Arctic air will periodically move into central
  and north- central Montana.

&&

.DISCUSSION...
/Issued 134 PM MST Mon Dec 22 2025/

 - Meteorological Overview:

Precipitation diminishes and ends this afternoon with the passage of
the responsible shortwave trough. Arctic air will move back
southward and brush north-central Montana this evening and tonight,
mostly impacting areas along the Hi-Line. A deepening trough along
the Pacific NW coast will send another elevated warm front through
the forecast area on Tuesday, resulting in more mountain snow and
some lower elevation precipitation. Recent model guidance has been
running a little less bullish with precipitation east of the
Continental Divide for the Tuesday through early Wednesday period,
but at least some scattered areas of light precipitation can be
expected. The warming aloft will also bring another opportunity for
spotty, light freezing rain/drizzle over the colder valleys.

The better chance of precipitation will come Wednesday into Thursday
when a shortwave ejects northeastward into the Northern Rockies. The
most notable change with this system from 24 hours ago is the warmer
temperatures aloft. While there is still an expectation for surface
level Arctic air to dive back southward into central/north-central
MT, the shallow cold profile no longer looks to be supportive of
widespread lower elevation snowfall, but rather lighter snow and
mixed precipitation, including light freezing rain and drizzle.
Mountain areas still look good for light accumulating snow during
this time.

The aforementioned trough churning along the Pacific NW coast looks
to finally head eastward into Montana Friday into Saturday for
another round of snow and a southward intrusion of Arctic air.
The cold air depth with this system should be sufficient for snow at
all elevations, but still most widespread in the mountains. Ridging
aloft then settles in for milder conditions later in the weekend
into early next week before troughing and colder air returns heading
into the new year. - RCG

 - Forecast Confidence & Scenarios:

At this time, precipitation on Tuesday into early Wednesday looks
minimal for most locations east of the Continental Divide. The main
concerns come with the arrival of a shortwave trough and the
southward advancement of an Arctic boundary. If this trough does
indeed lack colder air aloft, then central and north-central Montana
will be looking at scattered areas of light freezing rain/drizzle
late Wednesday through early Thursday morning while temperatures
fall in teens and 20s. NBM probabilities weakly highlight this
potential with around a 10 to 20% chance for a hundredth or greater
of ice accumulation. This situation will be closely monitored as
time progresses. - RCG

High Winds late Tuesday night through Wednesday Evening...

Climate anomaly indicators such as the NAEFS and ECMWF EFIs support
the potential for high winds throughout the Madison River Valley as
H700 flow increases from the south in wake of a northward lifting
warm front. H700 winds per NAEFS analysis are prog`d to reach
between 40-50kts from late Tuesday night and persist through much of
the day on Wednesday, with these values being anywhere from 2 to
nearly 3 standard deviations above normal. Furthermore, ECMWF EFIs
for both wind speeds and gusts on Wednesday range from 0.6 to 0.9
across most of Southwest Montana south of the I-90 corridor, which
indicates the potential for at least a climatologically unusual wind
event. While NBM4.3 probabilities for wind gusts in excess of 50kts
within the Madison River Valley only range from a 20-30% chance on
Wednesday the probability for sustained winds in excess of 34 kts
range from a 30-50% chance. These higher probabilities with respect
to sustained wind speeds seem reasonable given the anomalous H700
flow moving overhead, with the lack of a pressure gradient
orientated to the north of the valley helping to keep gusts on the
lower side. Give the 50/50 chance for sustained winds reaching high
wind criteria a High Wind Watch has been issued for the Madison
River Valley for the day on Wednesday. - Moldan


&&

.AVIATION...
23/00Z TAF Period

VFR conditions are expected across North Central and Southwestern
Montana over the next 24 hours. Watch for a few light showers
across Southwestern Montana tomorrow morning as some moisture
tries to cross the divide. Ludwig


&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  28  43  26  39 /   0  10  10   0
CTB  15  38  22  26 /   0   0  20  10
HLN  29  42  30  48 /   0  30  10   0
BZN  32  45  31  52 /  10  20  10  10
WYS  32  40  29  42 /  90  50  20  60
DLN  32  46  31  48 /  10  20  10  20
HVR  13  27  24  31 /   0  20  20   0
LWT  30  45  33  52 /  10  20  10   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Watch from late Tuesday night through Wednesday
evening for Madison River Valley.

&&

$$
http://www.weather.gov/greatfalls