466
FXUS65 KBYZ 032058
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
258 PM MDT Fri Oct 3 2025

.KEY MESSAGES...

- Elevated fire weather concerns in the far southeast corner of
  Montana (gusts 20-30 mph) through early evening.

- Turning much cooler and wetter this weekend as storm system
  moves across region.

- Several inches of high elevation snowfall and widespread
  precipitation at the lower elevations this weekend.

- High probability of a frost or freeze Sunday night.

&&

.DISCUSSION...

Through next Friday...

Satellite imagery shows a deep trof along the Pacific coastal
states, with SW flow aloft pushing moisture through the SW CONUS
and into the Rockies.

In immediate short term, we are monitoring elevated fire weather
over the SE corner of MT where a deeply mixed S to W wind with
gusts 20-30 mph is coinciding with the very warm temps and RHs
under 20%. These conditions should improve quickly as the sun sets
this evening.

Tonight: As the upper Pacific trough slides slowly eastward
we will see increasing moisture and diffluence aloft over our
west leading to some convective activity through the evening. A
few weak thunderstorms are possible along with scattered showers.
While the threat of thunderstorms decreases overnight, scattered
showers may continue as upper trough axis pushes into the Rockies.
Snow levels should generally remain >10kft thru 6 AM Saturday.

Saturday & Sunday: We confidently expect to see a very wet and
cooler weekend as upper trough tracks from Utah across Wyoming
while additional energy (and colder air) drops south from Canada
into the Rockies. Cross sections show the air mass becoming
saturated across most areas Saturday morning with northerly
upslope flow developing in the lower levels as well. Snow levels
will gradually drop through the day and into Saturday
night...going as low as 5.5-6k ft by Sunday morning in the
Beartooths. The best synoptic forcing looks to be Saturday into
Saturday night, especially in our western and central zones,
transitioning to the east thru Sunday. The probability for at
least 0.50" of precip is very high (60-100%) and the chance of
1.00" is a healthy 30-70%, greatest south over and near higher
terrain. Upslope areas should see 1-2" of precip with this system.
This will also be the first significant snowfall for the
mountains, and not just at the highest elevations. Thus, all
elevations above 6kft will see accumulating snowfall. In the case
of the Beartooth- Absarokas we are looking at 10-20" above 9kft.
We have upgraded the the Winter Storm Watch in effect for the
Crazy, Beartooth-Absaroka ranges to a Winter Storm Warning from
600AM Saturday to 600pm Sunday. Our current forecast only has a
trace of snow in the Red Lodge Foothills, but deterministic GFS
cross sections suggest we could see decent lift and northerly
upslope there late Saturday night into Sunday as snow levels fall
to near 6k ft. So would not be surprised to see 1-2 inches on
natural surfaces accumulate in the Red Lodge foothills. Current
probability of 1 inch at Red Lodge is 20% based on NBM data, but
sharp gradient of snow levels raises uncertainty. We will need to
monitor foothills for possible low end advisory (1-3 inches).

As for the Bighorn/Pryor Mountains...Colder air does not get into
the Big Horns region until after 600 pm Saturday. Northerly
upslope and upper forcing across this region is expected to lead
to decent precipitation with snow levels dropping to 6-7k ft. We
have issued a Winter Weather Advisory for the Pryors/Big Horns
from 600 pm Saturday thru Sunday evening. Six to twelve inches
are expected in the Northern Big Horns.

Precipitation should gradually taper down from NW to SE Sunday
night. With clearing and a surface high settling in, Sunday night
could yield the first widespread frost/freeze of the fall.
Billings has a 25% chance of reaching 32F, but surrounding
notoriously colder spots have greater potential (40% or higher).

Monday through Friday: Ensemble cluster analysis is in very good
agreement that we will be transitioning to a dry and warmer
pattern for next week. Look for a warming trend as upper level
ridging builds over our region. Temps Monday should be in the 50s,
60s Tuesday, and mid 60s to mid 70s after midweek. A few showers
are possible late in the work week over the mountains as flow
aloft backs to the SW, but this remains highly uncertain at this
time and would be of little overall impact.

Finally, it will be interesting to watch the evolution of the next
tropical storm which is expected to form off the coast of Mexico
over the next few days. Model/ensemble consensus takes this storm
toward Baja CA, with SW flow pushing associated moisture
northward toward MT/WY by next weekend. BT/JKL


.AVIATION...

18z Discussion...
VFR conditions will prevail for the first part of the period
before showers move in starting in ernest after 00z. Precipitation
will fill into the region from west to east starting as scattered
showers before it becomes widespread around 10z. Snow is expected
to accumulate in the mountains but no TAF site is expected to see
any frozen precipitation. As the rain becomes more widespread
into Saturday, CIGs are forecast to lower to MVFR with the
potential that VIS be reduced to MVFR as well. (KBIL and KLVM are
the most likely sites to see MVFR conditions.) Winds at all TAF
sites should also remain relatively light with no gusts over 20
kts. Mountains will be obscured for the entire period. WMR

&&

.PRELIMINARY POINT TEMP/POPS...

    Sat     Sun     Mon     Tue     Wed     Thu     Fri
-----------------------------------------------------------
BIL 050/055 042/049 034/058 037/064 041/070 045/070 042/066
    5+/R    97/R    20/U    00/U    00/U    11/U    11/U
LVM 042/053 033/047 025/056 028/064 034/069 036/069 036/066
    6+/R    98/R    20/U    00/U    00/U    11/U    22/W
HDN 047/057 041/052 031/058 032/067 036/071 040/070 038/068
    79/R    97/R    30/U    00/U    00/U    10/U    11/U
MLS 051/062 045/056 032/060 034/067 041/073 043/071 040/068
    37/R    93/R    10/U    00/U    00/U    00/U    10/U
4BQ 051/064 043/052 034/057 035/064 042/071 044/069 042/067
    16/T    +5/R    21/U    00/U    00/U    10/U    00/U
BHK 046/065 041/056 029/058 033/065 038/071 042/071 039/067
    14/R    +4/R    10/U    00/U    00/U    10/U    10/U
SHR 043/059 035/047 029/056 028/064 034/070 038/070 037/068
    48/R    +8/R    51/U    00/U    00/U    00/U    11/U

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Warning in effect from 6 AM Saturday to 6 PM MDT
      Sunday FOR ZONES 67-68.
     Winter Weather Advisory in effect from 6 PM Saturday to
      midnight MDT Sunday night FOR ZONE 171.
WY...Winter Weather Advisory in effect from 6 PM Saturday to
      midnight MDT Sunday night FOR ZONE 198.

&&

$$
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