818
FXUS65 KBYZ 130156
AFDBYZ

Area Forecast Discussion...Updated
National Weather Service Billings MT
756 PM MDT Sun Oct 12 2025

.KEY MESSAGES...

- Frost/freeze for most areas tonight. Most locations will see
  morning temperatures in the mid to upper 20s.

- Light snow accumulations (1-3") may impact US-191 north of Big
  Timber to Judith Gap for Monday morning commute.

- 30 to 60 percent chances for precipitation return, from Tuesday
  night through Thursday evening. High elevation snow
  accumulations possible (above 7000ft).

- Mainly dry and warmer next weekend.

&&

.DISCUSSION...

Today through Sunday...

Broad upper level trof is centered over SW Canada this afternoon,
with a couple of lobes of stronger energy rotating around its
periphery. The eastern lobe, that brought significant
precipitation (0.25 to 1.25 inches) to the area late Saturday into
this morning, is lifting northeast of the area at this time,
taking precipitation chances with it. Residual energy/instability
combined with a few breaks in the clouds will keep scattered
showers and maybe a rumble of thunder in the forecast for western
mountains and foothills this afternoon into early this evening.
Additional shower chances will persist over far SE MT associated
with exiting jetstream energy.

As we go into tonight the second piece of energy drops down the
west coast and deepens. This pattern adjustment brings
increasingly divergent flow aloft over the area as well as pulling
in easterly low level upslope flow in the low levels. The upper
level divergence combined with the low level upslope winds set up
a good precipitation producing period overnight into tomorrow over
the western mountains and foothills, possibly extending eastward
as far as a Columbus to Roundup line. Models are advertising 2 to
3 inches of snowfall possible late tonight through late Monday
morning along the US-191 corridor from north of Big Timber to
south of Harlowton (Melville vicinity). For Harlowton the
probability for at least an inch is sitting at 46%, with an 18%
probability for 2+ inches. So, the main concern with this light
snowfall is mainly with travel impacts Monday morning. The Metro-model
is a bit wishy-washy with how road temperatures will respond
overnight, showing temperatures getting down to 32 around 4 am and
staying right there through late morning. This suggests there
will be snow accumulating on road surfaces (US-191) around
sunrise, but not as much as models are thinking will fall in this
area. Contemplated a Winter Weather Advisory for this area given
the early season nature of this snowfall, but just not seeing
enough accumulation at this point to pull the trigger. However
will continue to advertise the potential for some locally slick
travel in that area for tomorrow mornings commute.

Morning lows will be chilly with most areas looking at mid to upper
20s. Cover any tender vegitation that you are trying to keep
going a bit longer into the fall. Bundle the kids up warm for
school tomorrow morning and leave a bit of time to scrape the
windshield and get the car warmed up.

Upper low continues to sag south away from the area Monday turning
the corner over Arizona and beginning to head our way late
Tuesday. This will make for a mainly dry afternoon Monday and a
dry day on Tuesday. As the upper low moves closer, expect stronger
upper level dynamics to develop over western zones Tuesday night
into Wednesday morning with increasing precipitation chances
(30-60%), spreading eastward to encompass the forecast area by
Wednesday evening. Upper trof lingers over the area through
Thursday evening with continued strong widespread precipitation
potential (most areas looking at around half an inch of
precipitation possible).

With this system arriving from the southwest, it will be warmer
than this weekends system and have higher snow levels. Snow levels
start out around 9500 feet Tuesday night, dropping to 8500 feet
Wednesday afternoon, and finally down to around 7000 feet
Thursday morning. Currently looking at 4 to 8 inches of snow above
7000ft, with the heaviest amounts really sticking above 8000ft
based on latest guidance.

Upper low exits to the east Friday with breezy westerly
(downslope) winds drying things out for the area. Ridging builds
in behind the system for a warmer and mainly dry weekend. Chambers

.AVIATION...

Rain/snow showers, becoming all snow can be expected along the
western foothills (KLVM through K3HT) into Monday morning.
Snow will gradually diminish through mid-day Monday. Low stratus
will develop and impact areas from KBIL to KSHR and areas west
tonight through mid-day Monday. Fog is possible through the
morning hours at KSHR. As a result, MVFR/IFR conditions are
anticipated at these sites as well as mountain obscurations over
south central MT. Lower confidence exists for fog across eastern
MT (KMLS, KBHK), but a 20% chance is still forecast (dependent on
cloud cover). TS/STP

&&

.PRELIMINARY POINT TEMP/POPS...

    Mon     Tue     Wed     Thu     Fri     Sat     Sun
-----------------------------------------------------------
BIL 030/044 033/051 039/054 041/055 040/058 038/057 038/062
    21/B    11/B    45/R    66/R    43/R    32/R    12/R
LVM 024/039 026/052 032/051 032/052 031/055 029/055 032/060
    52/S    22/O    67/R    76/R    43/R    42/O    13/R
HDN 028/051 032/055 036/057 039/054 037/060 035/057 034/064
    10/U    11/B    45/R    76/R    53/R    42/R    11/B
MLS 028/052 039/061 042/061 041/054 038/058 035/057 034/064
    00/U    11/B    35/R    66/R    43/R    21/B    01/U
4BQ 028/055 041/064 044/068 042/054 038/058 036/054 036/063
    00/U    11/B    23/T    65/R    32/R    22/R    10/U
BHK 022/052 035/057 038/059 040/055 035/056 032/055 031/061
    00/U    11/N    23/T    65/R    42/R    21/B    00/U
SHR 023/052 030/061 036/063 034/054 032/058 029/055 030/064
    00/U    21/B    34/R    76/R    43/R    42/O    11/U

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...None.
WY...None.

&&

$$
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