Norris, Montana Weather Forecast Discussion

043
FXUS65 KTFX 030743
AFDTFX
Area Forecast Discussion
National Weather Service Great Falls MT
143 AM MDT Fri Oct 3 2025
.KEY MESSAGES...
- Periods of rain early today across portions of the plains and
   vicinity, with a few showers and thunderstorms this afternoon.
- Initial push of cooler air arrives today into tonight, with
   areas of precipitation developing mostly over Southwest Montana
   late tonight into Saturday.
- Coldest push of air arrives late Saturday into Sunday, sending
   snow levels significantly lower. At least light snow
   accumulations in many mountains late Saturday night through
   Sunday.
- Coldest morning of the season so far on Monday.
&&
.DISCUSSION...
- Meteorological Overview:
Today:
Initial concerns today are related to a band of rain lifting
northeastward across western portions of the region early this
morning.  Sufficient mid-level (700mb) frontogenesis advancing
northeastward ahead of the base of a large scale trough off the
coast of northern CA will result in a period of rain this morning,
mainly for areas west of I-15. The frontogenetic nature of the rain
will result in a somewhat narrow band of rain, hence resulting in
noticeable differences in precipitation amounts over short distances
(Less than 50 miles).
This band lifts northeastward through the morning before beginning
to subside early this afternoon across the plains as forcing
weakens. Areas on the Hi-Line east of I-15 and west of US-87 will
have a narrow window to see light rain before the band subsides.
Attention then quickly turns toward Southwest Montana this afternoon
ahead of a cold front advancing southeastward from western Montana.
There appears to be a narrow window ahead of the front (Largely
south of US-12 and east of I-15) where sufficient surface heating
will result in marginal instability this afternoon. Should the
more aggressive scenario play out (Greater instability), there
would be a window ahead of the front for a few stronger
thunderstorms. Forecast soundings do not show much in way of DCAPE,
so the expectation would be for hail to be the greater concern,
especially given the overall cooler profiles (Surface temperatures
largely in the 60s).
The aforementioned front will result in the initial push of
cooler air into the region ahead of a more significant cool down
alter in the weekend.
Tonight into Saturday:
Heading into tonight, the upper trough mentioned previously near CA
will shift eastward into NV before shifting northeastward toward
UT/ID/WY heading into Saturday. A shield of precipitation looks to
extend northwest from this troughing beginning late tonight, but
ramps up more during the day Saturday across Southwest Montana and
vicinity, largely east of I-15. Although cooler air will be moving
in, the timing of the precipitation (During the day) helps mitigate
concern for accumulating snow away from the high peaks in Southwest
Montana east of I-15. Snow levels over the Gallatins/Madisons and
vicinity look to drop to around 7,500 ft Saturday afternoon. Rain
will be the precipitation type at lower elevations through Saturday.
Saturday night through Monday morning:
While larger scale troughing moves through WY and vicinity during
the day Saturday, a smaller scale trough on the western side of
broader troughing in AB/SK will be advancing southeastward toward
the Northern Rockies. This troughing arrives late Saturday into
Saturday night and brings the most significant push of colder air
across the region heading into Sunday along with another wave of
precipitation. Snow levels fall significantly with this trough,
resulting in at least light snow accumulations in many mountain
areas, even bringing brief opportunities for snow in higher elevation
areas near terrain. Areas that have the greatest potential for more
moderate impacts from snow include the Glacier NP area as well as
the Madisons/Gallatins/Tobacco Root mountains, where a Winter
Storm Watch remains in effect.
Precipitation gradually diminishes toward late Sunday into Sunday
night. Attention then turns to cold overnight lows by Monday morning
across all areas. Clearing skies behind the departing systems will
allow for temperatures to fall well into the 20s in most areas.
Fog will also be a concern Monday morning where skies are quickest
to clear.
Monday onward:
Upper level ridging is favored to redevelop across the west early
next week, allowing for another drier stretch, with temperatures
rising to near or a touch above average.
Confidence in the forecast decreases significantly after mid-week,
as ensemble spread increases associated with another period of upper
level troughing moving in across the Pacific Northwest. Magnitude
and timing of any troughing that does develop is low confidence. Add
on top of that that there is still a subset of guidance (~20% or so)
that favors ridging into late next week, it results in a wide range
of potential outcomes. -AM
- Forecast Confidence & Scenarios:
Thunderstorms today: The initial point of uncertainty is related
to just how much instability is able to be realized this afternoon
and evening across portions of Southwest Montana ahead of the
cold front. HREF probabilities for 250 m2/s2 surface based cape
are around 70% between WHitehall and Dillon, but fall to less than
10% for surface based cape in excess of 500 m2/s2. Should the
higher instability be realized, ensembles average effective shear
is around 30 kts, suggesting a few stronger thunderstorms will be
in the cards.
Mountain Snow Saturday in SW MT: Heading into Saturday, the main
precipitation shield associated with the upper troughing off to
the southeast will extend northwest into portions of Southwest
Montana. Deterministic soundings in BUFKIT suggest snow levels
fall to around 7,500 ft by Saturday afternoon over the
Gallatins/Madisons and vicinity. While many locations in these
ranges reside above 7,500 ft, warm ground raises significant
concern for the ability for snow to accumulate, especially in
areas closer to 7,500 ft. Additional complexity is in place given
the snow in these ranges mostly looks to fall during the day
Saturday. Hence, although snow will fall in these ranges Saturday,
confidence in accumulating snow is very low outside of the higher
peaks. A final complicating factor is that recent guidance has
trended slightly further south and east with the precipitation,
which would limit precipitation amounts in the aforementioned
ranges. For these reasons I did not elect to shift the start time
of the Winter Storm Watch earlier for the aforementioned ranges
(The Winter Storm Watch is in effect starting 6 PM Saturday).
Those planning to recreate in these areas should know that
conditions will be wet/raw where precipitation is falling, even if
at elevations where precipitation type is rain.
Cold front strength Sat Night: Another bit of uncertainty is
related to just how strong the Canadian cold front will be
Saturday night. NAM family of guidance suggests strong pressure
rises behind the front, which would indicate a period of gusty
winds. Meanwhile most other guidance is a bit more gentle with the
front, allowing the cold air to enter the region in a more
filtered fashion. The stronger front also results in snow levels
that are quicker to fall, which will be especially important for
any opportunities for snow down on the plains. -AM
&&
.AVIATION...
03/06Z TAF Period
Scattered showers track northeast across primarily western
portions of north-central and southwest MT through Friday morning
with mountain obscuration and brief MVFR conditions possible near
showers. An area of fog has developed near KBZN with some high
resolution model data also depicting this potential at KEKS.
Extensive mid-high cloud coverage should limit the extent and
duration of fog in these areas, but confidence is lower than
average. Otherwise, mainly VFR conditions are expected with an
increase in showers and potentially some thunderstorms late Friday
afternoon and evening. Hoenisch
&&
.HYDROLOGY...
There will be increased shower and isolated thunderstorm activity
this afternoon and evening, mostly over central and southwest MT.
While flooding is generally not expected, moisture levels will be
high enough to support rainfall rates up to or greater than a
quarter inch per hour. Flooding and or land slides over burn scars
can`t be ruled out should they undergo heavier downpours. - RCG/AM
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF  60  43  58  36 /  60  30  30  80
CTB  62  38  54  30 /  40  10  40  80
HLN  63  44  57  37 /  60  50  50  80
BZN  70  41  52  35 /  40  50  80  80
WYS  65  35  48  27 /  30  70 100  80
DLN  66  41  53  33 /  50  60  50  50
HVR  65  43  62  35 /  60  30  20  40
LWT  68  42  55  33 /  20  40  60  80
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from late Saturday night through Sunday
morning for East Glacier Park Region.
Winter Storm Watch from Saturday evening through Sunday
afternoon for Gallatin and Madison County Mountains and
Centennial Mountains.
&&
$$
http://www.weather.gov/greatfalls

NWS TFX Office Area Forecast Discussion