683
FXUS65 KBYZ 211957
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
157 PM MDT Thu Aug 21 2025

.KEY MESSAGES...

- Marginal risk (risk level 1 out of 5) for strong to severe
  storms in southeastern MT and northern WY this
  afternoon/evening.

- Very little precipitation expected over the next week.


&&

.DISCUSSION...

Today through Friday night...

Cloud cover is slowly burning off across the forecast area late
this morning in the wake of last nights frontal passage. High
temperatures will be around normal today, in the 80sF.

There is a Marginal Risk (risk level 1/5) for severe
thunderstorms along the MT/WY border, and all of Sheridan County.
The latest mesoanalysis depicts an area of moisture pooling in
this area today, especially in Sheridan County. A weak upper wave
will move across the region this afternoon, bringing increased
mid- upper level shear to the area (40+ knots of 0-6km bulk
shear). Surface winds in the southeast are out of the ENE,
bringing in the mentioned moisture and resulting in PWATs of 1 to
1.25". Additionally, an area of 850-700mb frontogenesis is shown
developing along the MT/WY border late this afternoon/evening. The
main risks with storms will be strong wind gusts up to 60 mph and
quarter size hail. Locally heavy rainfall is a secondary risk.

The chance for precipitation for the mentioned areas is 30 to 70%
this evening into Friday morning. The chance for precipitation
will increase (20-50%) northward overnight, including Custer and
Fallon counties. Otherwise, the chance for precipitation for the
rest of the forecast area is less than 25% (best chance in the
mountains).

Total precipitation amounts in the southeast range from a few
hundredths of an inch to half an inch, with locally higher
amounts possible. The chance for at least 0.1" of rain tonight
through Friday morning is 25 to 80%, greatest in Sheridan County
and along and south of US212 in Rosebud, Powder River, and Carter
counties.

Friday, upper level ridging will begin to build over the
northwestern US. Surface winds will remain easterly, which will
help keep temperatures in the 70s to low 80s. Dry conditions will
prevail Friday afternoon and into the weekend, despite easterly
flow at the surface.

Wildfire smoke will continue to impact the region at times, with
hazy skies. Currently, reductions to visibility or impacts to air
quality are expected to be minor.

Matos

Saturday through Thursday...

The extended period is shaping up to be rather quiet...with
regard to both convection and fire weather...as an upper ridge
axis remains to our west and we stay under a drier NW flow aloft.
This scenario will keep low level winds easterly, temps
comfortable and relative humidities seasonably elevated. Temps
should stay a bit cooler than normal Saturday through Monday, then
warm to near or a but warmer than normal by midweek as the ridge
axis begins to move slowly to the east.

Thunderstorm potential will be largely suppressed by the NW flow,
but monsoon moisture under the ridge over the northern great basin
may eke into south central MT and WY bringing some diurnal
activity over the mountains/foothills. Lower elevations should
stay dry, initially. By Wednesday/Thursday there are signs of weak
shortwave energy eroding at the ridge and bringing a bit greater
chance of weak/non-severe thunderstorms to lower elevations. This
evolution in the pattern is consistent w/ ensemble pwats going
from low values Sat-Tue to near or above normal thru the latter
half of the week.

JKL

&&

.AVIATION...

Expect VFR conditions to prevail through the period for most
sites. Shower and thunderstorm activity in southern MT and
northern Wyoming may result in reductions to flight category,
beginning around 21z today. The main threats with the strongest
storms will be gusty winds and hail up to quarter size. The most
likely time frame for thunderstorm impacts to KSHR is 21z to 03z.
Expect the chance for precipitation in SE MT and NE WY to decrease
through Friday morning. Reductions to slant range visibility are
possible at times due to smoke from nearby and regional wildfires.
Matos

&&

.PRELIMINARY POINT TEMP/POPS...

    Fri     Sat     Sun     Mon     Tue     Wed     Thu
-----------------------------------------------------------
BIL 060/078 054/082 053/081 053/081 055/085 058/085 059/086
    00/B    00/U    00/U    01/B    11/U    11/B    12/T
LVM 051/077 045/082 045/081 047/081 048/083 051/084 051/081
    00/U    00/U    00/B    02/T    12/T    12/T    33/T
HDN 060/080 053/082 051/082 052/083 052/086 055/087 056/086
    21/B    00/U    00/U    01/B    11/U    00/B    11/B
MLS 061/078 051/078 050/076 050/079 053/083 057/085 057/085
    10/B    00/U    00/U    00/U    00/U    00/U    01/B
4BQ 061/079 055/077 050/075 051/077 053/081 057/083 057/083
    63/W    00/U    00/U    00/B    11/U    10/B    11/B
BHK 058/077 047/076 045/073 045/076 049/080 052/083 054/083
    10/U    00/U    00/U    00/U    00/U    00/U    00/B
SHR 056/076 051/080 048/078 048/079 049/081 052/082 054/081
    43/T    20/U    00/U    02/T    12/T    11/B    12/T

&&

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

&&

$$
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