284
FXUS65 KBYZ 152348
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
548 PM MDT Tue Sep 15 2026

.KEY MESSAGES...

- Quiet Weather Wednesday.

- Increasing precipitation chances Thursday into the weekend.
  Locally heavy rainfall possible Friday into Saturday.

- Strong thunderstorms possible Friday east of Billings.

&&

.UPDATE...
Dry southwest flow aloft exists over our area, ahead of a
deepening trof along the Pacific coast and well north of monsoon
moisture. Weak energy skirting across southern Canada (split from
the Pacific trof which will evolve into a cut off low) will be
associated with a dry Canadian cold front that arrives early
Wednesday. In the meantime, a quiet night of weather is upcoming,
with breezy SE pre-frontal winds over the east. The Davis Coulee
Fire near Crow Agency did not produce much smoke today, and
conditions tonight are not supportive of fog, so have made some
minor adjustments to the forecast over the next 24 hours. JKL

&&

.DISCUSSION...
Rest of Today through next Monday...

Quiet weather pattern through Wednesday. Pattern becomes more
active Thursday into the weekend.

Zonal flow aloft over the area this afternoon is bringing sunny
skies and dry conditions to the region. Winds are slowly starting
to turn around to the southeast and will continue this trend
this evening, with a good southerly low level jet developing by
midnight over the eastern half of the forecast area. Expect wind
gusts 20 to 30 mph over the higher exposed hills across SE
Montana overnight into mid morning tomorrow. Lows tonight will be
a few degrees warmer over western zones tonight, but still
hovering in the upper 30s in the valleys. Lows will be near 40
degrees across central zones, warming toward 50 degrees over the
eastern zones where those stronger southerly winds will keep the
atmosphere stirred up.

A Pacific trof headed this way late tonight into the day
Wednesday, splits instead and sends a good deal of energy into a
closed low that develops over NorCal, while the rest of the energy
slides east across southern Canada. The result is that a
reinforcing push of cool air rides northerly winds into the area
Wednesday, but no precipitation is expected.

Wednesday night into Thursday the low level flow transitions from
northerly to southeasterly once again and and the moisture
advection associated with this change looks to be enough to get
isolated to scattered showers, maybe a thunderstorm, going
overnight into the day Thursday over SE Montana. Meanwhile, to the
west the NorCal upper low drifts eastward putting the southwest
mountains in increasingly diffluent southwest flow aloft. This
will bring increasing chances for showers and thunderstorms to
that area by Thursday afternoon, continuing into Thursday
evening. Shear profiles look good Thursday with SW winds aloft and
SE winds in the lower levels, however the CAPE values are 500 J/KG
so the threat for severe storms is very low Thursday.

That changes on Friday as the moisture levels increase with PWATs
jumping to more than 200% of normal over most of the forecast
area with 30 to 40kts of Bulk Shear thanks to the continued S-SW
flow aloft and SE winds in the lower levels. Medium range AI
severe products are starting to show severe storm probabilities
over areas from Sheridan county northeast into Custer county and
points east. Will see if that trend continues over the next few
days but something to keep in mind if you have outdoor plans
Friday afternoon. Further west the energy wrapping around the
slow moving upper low looks to bring widespread precipitation to
the western half of the forecast area by Friday afternoon, with
precipitation chances in the 60 to 90% range. These strong
precipitation chances spread into the eastern half of the forecast
area Friday night.

The latest model runs have come in wetter for Saturday into
Sunday. Yesterdays runs had the upper low opening up and
dissipating over the area which trended precipitation chances and
amounts downward quickly. The latest model runs hold the low
together as it moves through the area and track it further south
which is more favorable for precipitation over our area.
Precipitation potential continues into Sunday over the eastern
half of the forecast area as the upper low tracks eastward into
the Northern Plains at a fairly slow pace.

Ridging develops behind the upper low on Monday for dry
conditions.

Temperatures will stay in the 60s tomorrow for western and central
areas, with low to mid 70s for the east. Everyone gets into the
70s, a few lower 80s central and east, Thursday and Friday with
the surge of plains heat and moisture riding those increased
southeast winds. With the upper low over the region Saturday and
Sunday high temperatures stick near 70 degrees, then warm back
into the mid to upper 70s with ridging building in.

Light snow accumulations are starting to show up in the forecast
for the western mountains above 10kft for Friday night into
Sunday. This system is warmer than last weekends, so not expecting
snow levels to drop very low this weekend. However, if the upper
low becomes more organized and continues to track over our
mountains, the dynamic cooling could push those levels down
further. If you have plans in the mountains this weekend stay
tuned to the forecast for changes but be prepared for winter
conditions up high. Chambers

.AVIATION...

Surface winds will decrease early this evening at our TAF sites,
which generally have lower elevations than other parts of the
area. However, winds near the hilltops of southeast MT, mainly
east of KBIL-KSHR, will be stronger, generally 15-20 kt gusting
to 25-30 kt, and strongest east of KMLS-K00F. For the lower
elevations in areas east of KRPX-KBIL-KSHR, LLWS will develop
early this evening and then dissipate from west to east after 06z
Wednesday.

During the day Wednesday, a cold front moving to the southeast
will facilitate wind shifts, with winds becoming more
north/northwesterly over much of the forecast area in the midday
hours then turning more east-northeasterly in south central MT.
Wind speeds on Wednesday should generally be about 12-20 kt, with
gusts limited to 25 kt, the highest of which should be mainly
northwest, north, and east of KBIL.

VFR will prevail through the TAF period. RMS

&&

.PRELIMINARY POINT TEMP/POPS...

    Wed     Thu     Fri     Sat     Sun     Mon     Tue
-----------------------------------------------------------
BIL 044/069 048/075 056/079 054/071 051/074 049/077 050/076
    00/U    00/B    16/T    95/T    31/U    00/U    00/B
LVM 039/071 043/077 050/076 046/071 045/075 045/078 047/077
    00/U    12/T    27/T    85/T    21/U    00/U    01/U
HDN 041/070 045/079 053/081 051/072 046/075 043/079 044/078
    00/U    10/B    16/T    96/T    42/W    00/U    00/B
MLS 050/071 047/076 057/081 056/070 051/071 048/075 050/076
    00/U    01/B    14/W    97/T    54/W    11/U    00/B
4BQ 052/074 049/075 057/080 056/071 049/072 047/076 051/078
    00/U    12/T    14/T    97/T    54/W    10/U    00/B
BHK 046/077 042/072 052/078 051/069 048/071 045/074 047/077
    00/U    13/W    23/W    88/T    65/W    21/U    00/B
SHR 044/072 043/077 051/078 048/071 043/073 041/078 044/078
    00/U    12/T    18/T    98/T    42/W    01/U    00/U

&&

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

&&

$$
weather.gov/billings