093
FXUS65 KBYZ 210909
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
309 AM MDT Mon Sep 21 2026

.KEY MESSAGES...

- Areas of fog and low clouds this morning. Fog will be locally
  dense.

- Warmer and drier for the work week. 80s return midweek.

- Scattered showers and storms late Tuesday into Wednesday.

&&

.UPDATE...
Stratus and fog are widespread across lower elevations as of 09z,
but the low clouds are thus far dominant. Fog potential will
continue to increase between now and sunrise and will continue to
monitor the evolution of a very moist boundary layer. Any fog that
forms will be locally dense, producing visibility to a 1/4 mile or
less. Heads up for your morning commute.

Today will be dry & warmer but the easterly winds/moisture/poor
mixing will keep the warmup more gradual than it would otherwise
with above normal heights. Look for 60s to lower 70s for highs
today, coolest near the Dakotas border. Warming & drying trend
continues Tuesday (highs in the 70s to near 80F). Confidence is
increasing that a monsoonal wave from the southwest will bring a
period of showers and weak t-storms late Tuesday into Wednesday.
Pwats expected to increase to close to an inch over the east (2
standard deviations above normal), and there may be nocturnal
t-storms over the east late Tuesday night, per the timing of the
shortwave. Have raised pops and expanded TS coverage during this
time period.

JKL

&&

.DISCUSSION...

Next 7 Days...

As the slow moving upper level low finally makes its exit to our
east, we will see clearing skies and temps return to average.
While the next system to impact the region will zip through
Tuesday and Wednesday, the next large weather maker could impact
us this weekend, however a lot of uncertainty remains.

While some scattered showers will linger across fae SE Montana
and Northern Wyoming through the night, these will be light with
minimal accumulations. As the showers and clouds exit eastwards
and thin out through the morning, fog and low stratus will take
their place. The overall extent and density of this fog remains a
question as a little wind shift could mean the difference between
slight visibility reductions and dense fog. The short range
models are really hitting the locations that saw the most
rainfall over the weekend with Harlowton, Billings, and Hardin in
the bullseye of the latest HRRR runs. Previously the short range
models brought dense fog all the way up to the Beartooth/Absaroka
foothills but have since backed off. This seems to be due to a
surface high over YNP that has produced some weak downslope winds
that are fighting off the easterlies. That being said, the entire
forecast area has the chance of seeing fog and low clouds through
daybreak today. Use extra caution on your commute as visibility
can change rapidly over short distances.

In the wake of our weekend low, the ridge that was dominating the
southern plains builds northwestwards towards our area. This will
allow for temperatures to quickly rebound to near average today
and then push above average for the rest of the work week.
Readings in the 80s are possible for many locations Tuesday
through Friday so do not put away the t-shirts just yet, even with
Tuesday being the start of astronomical autumn.

Late Tuesday into Wednesday, remnant energy will ride along the
jet out of the Desert SW through our area. This will provide a
chance for some quick hitting showers and thunderstorms. There is
a potential that a storm or two in far eastern parts of the CWA
could produce some gusty winds or hail but we are simply still too
far out to get a good look at the event. Do note though that any
severe weather will be very hard to come by with this setup.

This upcoming weekend is our next shot at a potentially impactful
weather system. As of right now there is still a lot of spread
amongst models and ensemble members too. Right now the mean
solutions take the low just to our north which would result in
minimal precip and a potential strong wind event Saturday. Do not
alter any plans yet though as this forecast will almost certainly
change as we get closer to the event and start to see more
agreement amongst models. WMR

.AVIATION...

09z discussion.

Widespread low stratus and fog (IFR and lower) are affecting most
lower elevations at 09z, but thus far stratus is dominant. Fog
potential will increase through sunrise and it will be locally
dense (vsby to 1/4SM or less), but there remains uncertainty with
regard to specific impacts on TAF sites. All TAF sites are at risk
of seeing several hours of stratus/fog. For KBIL, development of
light Clarks Fork drainage winds (SSW) could lead to rapid fog
development at the airport, and this will continue to be
monitored. Look for fog/stratus to dissipate in the 15-18z time
frame. Otherwise, a few light showers may linger over far
southeast MT until sunrise. Building high pressure aloft will
bring dry conditions today and tonight. Fog is possible again late
tonight, but with less coverage than early this morning. JKL

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Tue     Wed     Thu     Fri     Sat     Sun
-------------------------------------------------------
BIL 070 048/077 053/079 052/081 053/083 053/071 046/068
    0/B 00/B    41/B    00/U    00/U    21/B    12/W
LVM 073 042/077 046/078 046/081 048/081 045/069 039/068
    0/B 00/B    20/U    00/U    00/U    21/B    22/W
HDN 071 043/078 049/079 047/085 050/085 049/074 043/071
    0/B 00/U    53/W    00/U    00/U    11/U    11/B
MLS 068 047/076 051/078 050/084 055/084 053/073 047/071
    0/E 00/U    45/T    00/U    00/U    11/U    11/B
4BQ 066 047/076 052/077 050/082 054/084 054/075 048/072
    1/E 00/U    43/W    00/U    00/U    10/U    12/W
BHK 064 043/071 048/078 048/083 051/083 051/076 044/071
    1/E 00/N    47/T    10/U    00/N    00/U    22/W
SHR 067 040/076 047/076 044/081 048/083 048/075 042/072
    1/B 00/U    43/W    00/U    00/U    01/U    12/W

&&

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

&&

$$
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