915
FXUS65 KBYZ 120704
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
104 AM MDT Sat Sep 12 2026

.KEY MESSAGES...

- Below average temperatures through the middle of next week.

- Occasional chances of showers (mainly light) through Monday.
  Scattered thunderstorms possible in southeast Montana Sunday
  evening, some possibly strong.

- Periods of overnight and morning low clouds and fog in the
  foothills through Sunday.

- Breezy west winds Monday; gusts over 50 mph possible near Big
  Timber and Harlowton.

&&

.DISCUSSION...

Next 7 Days...

The forecast for Saturday remains roughly the same. High
temperatures today will, once again, be roughly 10 degrees below
average for most locations. The main branch of the jet stream
remains overhead today which will allow for scattered showers
across the CWA due to increased synoptic lift in the right-entrance
region of a 500mb jet streak. The highest coverage of precip will
be in the plains of southeast Montana. Expect the coverage of
showers to decrease throughout the day, as the jet streak moves
east, leading to a mostly dry Saturday night.

Models continue to trend the Sunday shortwave farther to the
north. This is further solidifying that the once good
precipitation event, is now barely existent for for forecast
area.  With this more northerly track of the low now, we will
actually see a slight temperature rebound on Sunday. There is
still a large model spread on how much temps will rebound, but
highs near average are possible before another push of cool air to
start the work week.

With much of our area now in the "dry slot" of the low on Sunday,
there is a chance that some stronger thunderstorms may develop in
the eastern part of the CWA. During the afternoon and evening
Sunday, a cold front will push from west to east across the area
acting the the primary source of lift for any convection. Due to
the cooler temps, modeled MU-CAPE values remain under 1000 J/Kg
with surface CAPE under 500 J/Kg in recent runs. This would be
plenty sufficient though with the strong source of lift, the cold
front, greatly aiding CI as the it pushes through Sunday evening.
Additionally, shear values in SE Montana will be in the 30-60kt
range due to the proximity and location of the upper level low.
While 60 kts may rip the storms apart, the "lower" values will be
perfect to sustain any updrafts that can establish themselves. In
terms of moisture, PWAT values are forecast to exceed 1" in the
eastern 1/3 of the CWA ahead of the FROPA which will be more than
sufficient for thunderstorm development. The CAMs that run out
that far are depicting some strong to severe storms near the Black
Hills late Sunday and just clipping SE Montana. It is well within
the realms of possibility that these storms start to trend
farther north, just as the parent low did, over the next 2 days.
In terms of thunderstorm hazards, while every strong to severe
storm is capable of strong winds, it looks like the main threat
would be the potential for large hail. Additionally, any storm
that can become more surface based could produce a brief tornado.

Monday is looking increasingly windy. As the upper level low
migrates east Sunday night into Monday morning, the stronger mid
to upper level winds will be on the move with it. There is,
naturally, still some disagreement on timing and progression of
this feature. Both the ECMWF and GFS show 50kt 700mb winds over
the western portion of the CWA by 15z Monday with a slow and
steady eastward progression of this maximum through the day. While
surface winds will be breezy through the entire region all day,
the strongest gusts will likely occur with the jet max overhead.
During the late morning and early afternoon hours, when the
strongest winds aloft are westerly over the foothills, there
appears to be a good signal for gap enhancement along the US-191
corridor (Big Timber and Harlowton). Ensembles do have several
members with surface winds touching 50 kts in both locations
midday Monday. Trends will be monitored as this appears to be the
first impactful gap wind event of the fall. Not to be forgotten
though, the entire CWA could see gusts of 35 to 45 mph during the
day Monday.

Through the middle of the week we will remain under the main
branch of the jet stream which will allow for near to just below
average temperatures to linger. There are repeated chances for
isolated showers continue with these cooler temperatures due to
the strong jet dynamics overhead in addition to weak vort maxes
passing through. Towards the end of next week there are some
hints that a similar shortwave may move through the region again.
WMR

.AVIATION...

Banded precipitation is expected to persist across southeast MT
through the period mainly affecting KMLS. About a 30-40% chance
exists for low clouds to bring MVFR conditions to foothills
locations (KLVM, KSHR) overnight, clearing by 18Z today. TS

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Sun     Mon     Tue     Wed     Thu     Fri
-------------------------------------------------------
BIL 066 046/074 051/069 044/071 046/068 046/078 049/078
    1/B 01/B    20/N    00/U    01/B    00/U    11/B
LVM 067 040/074 040/065 036/070 039/068 040/078 044/078
    1/B 10/N    30/N    00/U    01/U    01/U    11/U
HDN 070 042/079 047/071 039/074 041/071 040/080 042/080
    1/B 00/B    30/N    00/U    00/B    00/U    11/U
MLS 063 046/072 052/070 042/071 047/071 045/078 047/079
    2/W 10/N    50/N    00/U    20/B    00/U    11/U
4BQ 067 047/074 053/072 042/073 047/072 045/080 049/080
    2/W 10/N    50/N    00/U    21/B    10/U    12/W
BHK 063 040/070 047/071 037/071 041/072 040/079 044/080
    2/W 10/N    72/W    00/U    31/B    10/U    12/W
SHR 071 041/081 046/071 037/073 040/070 039/078 043/079
    0/B 11/B    30/U    00/U    00/U    11/U    22/W

&&

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

&&

$$
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