Riverview Colony School Montana Weather Forecast Discussion

350
FXUS65 KTFX 140539
AFDTFX
Area Forecast Discussion
National Weather Service Great Falls MT
1139 PM MDT Mon Oct 13 2025
Aviation Section Updated.
.KEY MESSAGES...
- Reduced visibilities due to fog are possible tonight and
   Tuesday morning across portions of Southwest, Central, and
   North Central Montana.
- Another round of mainly mountain snow will return to Southwest
   and portions of Central Montana from Tuesday through Thursday.
- Temperatures slowly warm to near average by the end of the week.
- Periods of breezy to windy conditions are expected heading into
   the weekend.
&&
.UPDATE...
/Issued 854 PM MDT Mon Oct 13 2025/
The main concern for tonight through Tuesday morning is lingering
low level moisture from today`s snow system bringing in low level
stratus clouds and patchy fog across the region. Fog can become
locally dense at times, but currently I am not expecting
widespread dense fog. Therefore, I`ve held off on a dense fog
advisory for now, but we will monitor trends throughout the night.
Forecast soundings show deep moisture at the low levels, bringing
the slight chance for sporadic, brief freezing drizzle across the
region overnight. Temperatures dropping to below freezing
overnight can cause wet pavements to freeze, creating icy spots
along roads and bridges. Low level stratus can also bring
additional light snowfall to the Rocky Mountains overnight.
Another disturbance coming from ID will move north into Southwest
MT and the Tuesday morning, bringing another round of light
snow/wintry mix. Little to no accumulations are expected at lower
elevations and up to 1-2" of snow at the higher peaks.
-Wilson
&&
.DISCUSSION...
/Issued 854 PM MDT Mon Oct 13 2025/
- Meteorological Overview:
A closed low diving southward along the Pacific Northwest coast
will continue to support difluent flow over the Northern Rockies
for the first half the week. Moisture and weak shortwaves moving
in from the southwest will bring periods of rain showers and
higher mountain snow tonight into Tuesday, mostly for southwest
MT. The cold air over central and north-central MT will slowly
retreat northward heading into mid- week.
The Pacific Northwest closed mid- level low is expected to peak
in intensity over central CA before weakening and swinging
northeastward through the Great Basin and eventually reaching
eastern MT by around Thursday. The evolution of this feature will
be complex as it approaches the region, so the precise locations
of its low pressure center(s) and resultant precipitation
locations is still a bit on the fuzzy side. Overall expect the
most widespread rain and mountain snow to occur between Tuesday
night and Friday. With milder Pacific air moving in, snow impacts
look to be on the minor side and mostly confined to mountain
areas.
Ridging aloft with stronger westerly flow looks to at least
briefly move through the Northern Rockies heading towards the
weekend followed by more passing troughs in an increasingly
northwesterly flow aloft. This will result in periods of breezy to
windy conditions, though the timing details still need to be
worked out depending trough and ridge phasing. - RCG
- Forecast Confidence & Scenarios:
Fog tonight and Tuesday morning...
Both NBM and HREF guidance support the potential for reduced
visibilities due to fog development from the late evening hours
tonight through the morning hours on Tuesday. This will be
especially true where winds become light and variable and/or upslope
in nature, along with where skies partly clear. While surface winds
are expected to decrease through the overnight hours tonight the
biggest source of uncertainty with respect to fog developing is
with respect to cloud cover, with latest HREF guidance supporting a
50-75% chance for the total cloud cover to fall below 37.5% (mostly
clear skies). The one exception to this will be along and west of
the I-15 corridor where low level northeast to easterly flow will
help to maintain chances for light snow and/or low stratus for much
of the overnight hours.
Mountain Snow from Wednesday through Thursday ...
NBM probabilities for snowfall accumulations of 2" or more range
from a 25-35% chance for mountain passes like Kings Hill, Raynolds,
and Targhee throughout the timeframe; with the highest probabilities
(i.e. 60+% chance) being at or above 7500ft in elevation for all of
the mountains in Southwest and Central Montana. NBM probabilities
for 8" or more of snow within the Madison/Gallatin Ranges and
Tobacco Root and Gravelly Mountains range from a 25-50% chance for
elevations at or above 8000ft, which would be impactful for those
outdoor recreationists. ECMWF EFIs, particularly from Wednesday night
through Thursday afternoon, across Southwest Montana range from 0.5
to 0.6 and indicate an increasing potential for a climatologically
unusual snowfall event here. This timeframe bears watching given
continued outdoor recreation (i.e. hunting season), especially for
the mountains south of the I-90 corridor and east of the I-15
corridor in Southwest Montana. - Moldan
&&
.AVIATION...
14/06Z TAF Period
Low stratus clouds will continue to build in overnight and through
the morning. MVFR to IFR cigs are likely with isolated LIFR.
Patchy fog will continue across the region through Tuesday
morning, with a slight chance for locally dense fog. West
Yellowstone is the exception, with it likely to have dense fog
through Tuesday morning. Light snow lingers across North Central
MT during the overnight hours. There is an isolated chance for
brief freezing drizzle as well, but confidence in pinpointing it
impacting a specific terminal is low. Another wave of
precipitation from ID will lift north into Southwest MT Tuesday
morning, bringing light snow/wintry mix and rain. There is some
uncertainty in the timing of this wave, and if afternoon
thunderstorms will impact terminals. There will be mountain
obscuration from low clouds and precipitation. -Wilson
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF  25  40  28  40 /  20  20  30  40
CTB  23  40  21  46 /  20  20  20  20
HLN  25  41  29  41 /  20  30  30  60
BZN  23  48  30  44 /  20  40  60  70
WYS  25  50  27  42 /  50  70  80  90
DLN  26  48  33  45 /  30  30  60  60
HVR  24  48  29  47 /  20  20  20  50
LWT  22  46  29  40 /  20  20  60  60
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
http://www.weather.gov/greatfalls

NWS TFX Office Area Forecast Discussion