Sumatra, Montana Weather Forecast Discussion

585
FXUS65 KBYZ 040811
AFDBYZ
Area Forecast Discussion
National Weather Service Billings MT
211 AM MDT Sat Oct 4 2025
.KEY MESSAGES...
- Strong weather system brings wet and much cooler conditions
  this weekend.
- Widespread precipitation today and Sunday, with significant
  mountain snowfall.
- High probability of a frost or freeze Sunday night.
- Dry with a warming trend next week.
&&
.DISCUSSION...
Through next Friday...
Satellite imagery shows upper low over eastern NV with strong
diffluence noted over UT into southeast ID and western WY. There
are currently a couple bands of showers in our cwa. Mid level
winds are beginning to back in central WY (in response to the
approaching low) and mesoanalysis shows frontogenesis increasing.
Thus, expect precip coverage to increase steadily between now and
sunrise. Energy lifting out of the great basin will (w/ very high
confidence) bring widespread precip today and tonight. To our
north there is energy dropping thru northern BC. This feature will
reach the northern Rockies tonight and bring us colder air Sunday
and Sunday night. It is this secondary clipper that offers the
most uncertainty with regard to snow levels and precip during the
latter portion of the weekend. Stress continued uncertainty here.
A period of strong ascent and deepening upslope winds will bring
a healthy period of rain and mountain snow today and tonight, with
heaviest precip over west/central parts today shifting to the east
tonight. Snow levels start today around 11kft (per mesoanalysis)
and fall to about 8kft by sunset, then 6kft Sunday morning as the
Canadian wave arrives. Some of its energy drops to eastern ID
Sunday, a favorable track to keep ascent lingering thru most of
tomorrow over our west/south. We should see a trend toward height
rises Sunday night as energy drops into WY, and precip should
taper off in our forecast area during this time. Overall, precip
of 0.50-1.50" is expected, with up to 2" in southern upslope
areas. The probability of a half inch or more is 65-95% (lowest
north), and there is still a reasonable 20-50% chance of exceeding
1.50" (greatest along southern foothills). This event should put
an end to our wildfire season.
Mountain snowfall will be heaviest above 8kft but accumulations
will drop to as low as 6kft. The probability of at least 12" above
8kft is 60-80% over north aspects of the Beartooth-Absarokas, and
30-50% over the Crazy, Pryor and Bighorn Mountains. Anyone
thinking about venturing into the high country this weekend should
be prepared harsh wintry conditions. Foothills snow down to
5-6kft is a possibility by Sunday night but as already mentioned
this is much more uncertain. Places like Red Lodge and Story could
see some wet snow accumulation toward the end of this system.
Latest probability for an inch or more of snow at Red Lodge has
risen to 40%. Do not see any scenario in which snow levels fall
lower than 5kft, so places like Livingston and Sheridan will not
be impacted (though snow will likely affect I-90 over Bozeman
Pass).
Many locations should see a frost or freeze Sunday night, and
perhaps Monday night, but it looks like cloud cover may play a
role in Sunday night temps. Something to monitor if you have
sensitive outdoor plants. Billings has a 30% chance of reaching
32F Sunday night, but surrounding notoriously colder spots have a
much greater potential (40% or higher).
Monday through Friday: High confidence for a drying and warming
trend as upper level ridge reestablishes itself. Look for temps in
the 50s Monday, 60s Tuesday, and mid 60s to mid 70s for the
remainder of the week. There may be a shortwave moving across
southern Canada that brings a bit of cooling by Thursday or
Friday, but ensembles show large spread by this time. However that
pans out, the next reasonable chance of precip looks like next
weekend.
Finally, it will be interesting to watch the evolution of the
next tropical storm which is expected to form off the SW coast of
Mexico over the next couple days. Model/ensemble consensus takes
this storm toward Baja CA, and it is possible that associated
moisture gets injected into the southerly flow on eastern flank
of next Pacific coast trof...possibly raising precip chances in
MT/WY next weekend. High uncertainty here, but interesting
nonetheless.
JKL
.AVIATION...
Scattered showers and isolated thunderstorms continue to move
through the region. Sites impacted by this activity early this
morning include K3HT, KMLS, KSHR. Rain showers will become more
widespread today and persist through Sunday. Periods of MVFR to
IFR conditions will be possible under the heaviest showers.
Mountain obscurations are expected through the forecast period
with snow showers. Frozen precipitation is NOT forecast for any
terminals through the period. Matos
&&
.PRELIMINARY POINT TEMP/POPS...
Tdy Sun     Mon     Tue     Wed     Thu     Fri
-------------------------------------------------------
BIL 055 042/050 034/057 037/065 041/071 044/070 041/071
    +/T +8/W    31/U    00/U    00/U    00/U    00/U
LVM 053 035/046 025/056 027/065 033/070 036/068 036/071
    9/T 89/W    30/U    00/U    00/U    00/U    11/U
HDN 057 041/052 033/057 031/066 034/072 038/070 036/071
    +/T +8/W    31/U    00/U    00/U    00/U    00/U
MLS 062 044/056 033/059 033/066 040/073 042/071 039/071
    8/T +5/W    10/U    00/U    00/U    00/U    00/U
4BQ 064 042/052 034/055 034/063 042/072 043/069 039/070
    6/T +9/W    21/B    00/U    00/U    00/U    00/U
BHK 066 041/055 030/057 032/065 039/072 041/071 037/069
    5/T +5/W    10/U    00/U    00/U    00/U    00/U
SHR 060 041/047 029/054 027/064 032/071 038/069 036/071
    9/T +9/W    61/B    00/U    00/U    00/U    00/U
&&
.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Warning in effect from 6 AM this morning to 6 PM
      MDT Sunday FOR ZONES 67-68.
     Winter Weather Advisory in effect from 6 PM this evening to
      midnight MDT Sunday night FOR ZONE 171.
WY...Winter Weather Advisory in effect from 6 PM this evening to
      midnight MDT Sunday night FOR ZONE 198.
&&
$$
weather.gov/billings

NWS BYZ Office Area Forecast Discussion