540
FXUS65 KBYZ 170712
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
112 AM MDT Thu Sep 17 2026

.KEY MESSAGES...

- Isolated to scattered showers and thunderstorms this afternoon
  and evening. Locally heavy rain possible over SE Montana with
  any showers/thunderstorms.

- A few strong thunderstorms are possible, mainly around and east
  of Billings Friday afternoon and evening.

- High chance for widespread precipitation Friday afternoon
  through the weekend, with the potential for locally heavy
  rainfall through Saturday night.

- Chance for at least half an inch of rainfall is greater than 70
  percent across southern Montana and northern Wyoming. The chance
  for at least 1 inch of rainfall is 40 to 80 percent, greatest
  across south-central Montana.

&&

.DISCUSSION...

Today through Wednesday...

Patchy fog may develop amongst the river valleys and lower
elevations around and east of Billings this morning. The latest
HRRR shows this with reduced visibilities. Will continue to
monitor this through the morning hours.

Southeasterly surface winds will spread across the area today,
bringing in moisture from the Plains. Aloft, an upper shortwave
will move through the region this afternoon ahead of a parent
upper low. Isolated to scattered showers and a few weak
thunderstorms are in the forecast over the mountains of
southwestern Montana as well as across southeastern Montana and
northern Wyoming. The chance for precipitation across south-
central Montana is lower, with weaker forcing available. A few
stronger thunderstorms are possible over southeastern Montana,
capable of producing gusty winds and heavy rainfall.

Precipitable water values will increase today and linger through
the weekend as the parent low moves into the region. The latest
ensemble guidance depicts PWAT values exceeding 200% of normal by
Friday. This will bring the risk of very heavy rainfall with
showers and thunderstorms Friday through Saturday. There is a risk
for a few stronger thunderstorms on Friday, with the low digging
through eastern Idaho. Model soundings depict long and skinny CAPE
profiles for much of the area, though the best instability is
shown mainly east of Billings. Weaker shear could hinder stronger
convection though, along with weaker daytime heating. The latest
SPC outlook highlights much of Montana and Wyoming in a General
Thunderstorm Outlook for now, but continue to monitor the forecast
for potential updates.

The main concerns with showers and thunderstorms Friday and
Saturday will be erratic wind gusts and very heavy rainfall.
Widespread rainfall is currently forecast, with the probability
for at least 1 inch of rainfall at 40 to 80%, greatest across
south-central Montana and the Bighorn Mountains. WPC has a
marginal risk for excessive rainfall over the area both Friday and
Saturday now. So, plan on a wet weekend, especially Saturday, if
you have outdoor plans and have a way to get weather alerts in
case flood advisories or warnings become necessary.

Uncertainty remains with the progression of this system over the
weekend. The latest GFS ensemble has trended closer to what the
ECMWF ensemble has been showing, with the upper low sliding
eastward through Sunday. Previous runs of the GEFS were moving the
system out of the region faster. Widespread precipitation looks
to persist through Sunday mainly across southeastern Montana and
northern Wyoming. Deviations to the track could keep precipitation
further west into the mountains and foothills west of Billings.
However, the latest trends show precipitation ending by Sunday
afternoon for locations around and west of Billings at this time.

This system does not look to be very cold, so the chance for
mountain snow is not as high as last weekends system. However,
several inches of snowfall are in the latest forecast for the
highest elevations of the Absaroka/Beartooths and Crazy mountains
this weekend. Will continue to monitor this situation to see if
impacts to the Beartooth Highway would necessitate an advisory,
but at this time it does not appear an advisory will be needed.

Matos/Chambers


.AVIATION...

There is about a 30% chance for fog/low stratus to develop
tonight from 09-15Z mainly across southeast MT (KMLS, KBHK, K97M).
Scattered showers and isolated thunderstorms are expected to
begin moving up from the south mid day. The best chances for a
thunderstorm looks to be along the foothills (~20-30%). Main
concern with any thunderstorm will be gusty winds and heavy rain.
Any of these thunderstorms will likely drop conditions to
MVFR/IFR. TS

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Fri     Sat     Sun     Mon     Tue     Wed
-------------------------------------------------------
BIL 077 055/081 054/065 050/071 049/078 051/080 051/081
    0/B 04/T    +9/T    74/W    10/U    00/U    00/U
LVM 079 050/077 048/065 045/074 045/079 047/080 047/081
    3/W 28/T    ++/T    71/B    00/U    00/U    01/U
HDN 081 052/082 052/068 047/071 045/079 047/082 047/083
    0/B 12/T    +9/T    87/T    10/B    00/U    00/U
MLS 081 057/082 056/069 051/069 049/076 050/080 051/082
    0/E 01/B    99/T    87/T    21/B    00/U    00/U
4BQ 079 056/081 056/070 052/067 049/076 050/081 051/083
    2/W 41/B    9+/T    98/T    41/B    00/U    10/U
BHK 077 052/079 051/070 048/067 046/074 047/079 048/082
    0/N 30/B    57/W    87/W    31/B    00/U    01/U
SHR 078 049/081 049/068 044/068 042/077 044/081 045/083
    4/T 25/T    ++/T    97/T    31/U    00/U    00/U

&&

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

&&

$$
weather.gov/billings