419
FXUS65 KBYZ 012101
AFDBYZ

Area Forecast Discussion...Updated
National Weather Service Billings MT
201 PM MST Sun Nov 1 2026

.KEY MESSAGES...

- Patches of dense fog continue early this afternoon for portions
  of south-central Montana. Prepare for significant reductions to
  visibility.

- Widespread precipitation expected this afternoon through Monday.
  Well above normal precipitation amounts forecast for southeast
  Montana.

- Moderate to heavy snowfall expected for north and west aspects
  of the Absaroka/Beartooth and Bighorn Mountains through Monday.
  Very difficult conditions expected in the back country as well
  as travel through the Bighorns.

- Windy conditions on Monday, gusts 25 to 45 mph. A few gusts of
  50 mph or higher in Southeast Montana and Northern Wyoming.

&&

.DISCUSSION...

Rest of Today through Saturday...

While widespread dense fog has largely ended, current
observations and model trends show patches of dense fog continuing
into this afternoon. Areas impacted include Stillwater,
Yellowstone, Musselshell, Treasure, Bighorn, and portions of
Carbon County. As a result, the Dense Fog Advisory has been
extended until 2 PM this afternoon for reductions to visibility to
a quarter mile or less. Please use caution when traveling.

An upper trough is beginning to impact the Northern Rockies as it
progresses through the Mountain West into the new week. This
system will bring an abundance of atmospheric moisture to the
region, with precipitable water anomalies of nearly 300% over
southeast Montana into Monday. The liquid precipitation forecast
is shown as an extreme event for this time of year, with the ECMWF
EFI (Extreme Forecast Index) displaying values of 0.8 to 1.0
(with 1 being the maximum). Values of 0.8 or greater signify an
extreme or very unusual event. More on this shortly.

Showers have begun to develop over south-central Montana and will
continue to spread across the entire forecast area through this
afternoon and last into Monday. Widespread rainfall is expected,
while snowfall will occur in the mountains. Moderate to heavy
rainfall is expected south and east of Billings where there 0.75
to 1.5 inches of rainfall is forecast. The latest probability for
greater than 1 inch of rainfall is 60 to 90% for portions of Big
Horn and Treasure Counties and all counties to the east. The
probability for at least 2 inches of rainfall for the same area is
10 to 30%. For portions of northern Wyoming, rainfall up to or
greater than an inch are possible although confidence is lower.
This is partly do to a developing surface low in southern Wyoming
that may result in some drier periods over the next 24 hours. The
probability for at least a half inch remains high (60 to 85%)
though. For the rest of south-central Montana several tenths of
an inch of rainfall are in the forecast, though amounts are lower
going north and west of Billings. The probability for at least
half an inch of rain is 40 to 90% (greatest around Billings and
the Absaroka/Beartooth foothills).

Circling back to the EFI discussion, the single day precipitation
record for the Miles City Airport in November is 1.17" on
November 1st of 1957. For the upcoming event, the forecast has 1
to 1.4 inches of rainfall in the Miles City area. It does not
appear as though KMLS will set a new single day record, as several
tenths of an inch of rain are forecast for this evening splitting
the storm total across the first two days of the month. While a
single day record for KMLS looks unlikely, the average
precipitation total for the month of November at KMLS from 1990 to
2020 was 0.33". Across the entire period of record for KMLS
(records began in 1937), the average for November is 0.42". In
other words, this is going to be a very wet month after just 2
days.

For Sheridan, the single day November precipitation record
occurred on November 9th, 1978 when 0.85" of precipitation fell.
For this event around 3/4 of an inch are forecast for Monday. A
single day record could be broken. For the month overall, the
average from 1990 to 2020 was 0.76". The period of record goes
back to 1907 and the average since then is 0.78". KSHR may surpass
the monthly average after two days as well.

In the mountains, snowfall will begin tonight and last through
Monday afternoon. North and west aspects of the
Absaroka/Beartooths and the Bighorns will be favored. This system
will not bring much cold air with it, although snow levels drop as
low as 5,500 feet Monday morning. A rain/snow mix will start in
the high country before transitioning to all snow tonight. For the
Absaroka/Beartooths, 4 to 8 inches of snowfall are forecast
though locally higher amounts are possible. In the Pryors, up to 4
inches are forecast. For the Bighorns, 5 to 10 inches are
forecast with locally higher amounts possible. The majority of
accumulations in the Absaroka/Beartooth and Bighorn Mountains will
fall above 7,500 feet. With snow levels as low as 5,500 feet,
foothill locations such as Red Lodge could see some light snowfall
as well although accumulations will be minimal (less than an
inch).

A cold front is expected to move across the area tonight into
Monday, this will bring widespread breezy north-northwest winds
with gusts in the 20s to 40 mph. Windier conditions are forecast
for southeast Montana and northern Wyoming with gusts in the 40s
to low 50s mph. The probability for gusts of 50 mph or greater in
Sheridan County is 40 to 90%, greatest along the Johnson County
line. The probability for gusts greater than 60 mph in Sheridan
County is around 20 to 40%, almost exclusively along the Johnson
County line. For locations in southeast Montana, the probability
for 50 mph is 40 to 80% along and east of State Highway 323 and
greatest along the border. The probability for 60 mph winds is 20%
or less.

The combination of snowfall and windy conditions in the Bighorns
will result in very difficult conditions for those traveling along
Highway 14, as well as those in the back country. Because of
this, a Winter Weather Advisory is in effect until 8 PM MST Monday
with up to 11 inches of snowfall and winds gusting to 50 mph.
Please be prepared if you have plans in the Absaroka/Beartooth,
Pryor, and Bighorn mountains during this time.

Ridging is shown rebuilding Tuesday through midweek, with warmer
seasonable temperatures (50sF) and mostly dry conditions. An
occasional disturbance in the flow pattern may bring an isolated
shower or two into the mountains.

Matos

.AVIATION...

Persistent fog and low are continuing to bring areas of IFR/LIFR
conditions into early afternoon. There may be a period of
local VFR briefly at some sites in the west (ie KLVM, KBIL)
around midday. Then, as precipitation becomes more widespread this
afternoon, MVFR/IFR conditions will be common. Mountains will be
obscured through the period. Expect occasional local reductions
to LIFR tonight into Monday morning, especially near KMLS.
Precipitation will begin to end from west to east late Monday
morning. Winds become breezy out of the northwest late this
evening into Monday morning, with widespread gusts of 25 to 40
kts. Archer

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Mon     Tue     Wed     Thu     Fri     Sat
-------------------------------------------------------
BIL 047 040/047 032/055 034/052 033/056 035/057 036/054
    9/W +9/W    10/B    00/B    00/B    00/B    20/U
LVM 047 032/045 024/055 030/052 027/054 028/053 028/052
    8/W +7/W    00/B    00/B    00/U    11/B    30/U
HDN 052 036/047 027/057 027/054 027/057 029/059 033/056
    7/W ++/W    10/B    00/B    00/B    00/B    31/U
MLS 054 041/046 030/052 030/052 030/054 031/055 035/053
    7/W ++/W    10/U    00/B    00/B    00/U    11/B
4BQ 058 041/044 029/053 030/052 030/055 032/056 036/053
    7/W ++/W    50/U    00/B    00/B    00/U    21/B
BHK 058 040/050 028/050 026/053 026/053 029/055 030/051
    3/W ++/W    40/B    00/U    00/B    00/B    11/B
SHR 051 031/044 025/057 027/054 026/057 028/058 030/055
    5/W ++/W    30/U    00/B    00/U    01/U    31/N

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory in effect from 11 PM this evening to
      8 PM MST Monday FOR ZONE 171.
WY...Winter Weather Advisory in effect from 11 PM this evening to
      8 PM MST Monday FOR ZONE 198.

&&

$$
weather.gov/billings