661
FXUS65 KBYZ 280144
AFDBYZ

Area Forecast Discussion...Updated
National Weather Service Billings MT
744 PM MDT Wed Aug 27 2025

.KEY MESSAGES...

- Normal to slightly below normal temperatures this week.

- The chance of showers and thunderstorms return to the region
  Thursday through Saturday (moderate to high chance).

- Showers and thunderstorms through Saturday could produce locally
  heavy rainfall. Use caution if recreating, especially near
  recent burn scars.

&&

.UPDATE...

Area of low level southeasterly flow is pulling in some stronger
moisture from South Dakota into south central portions of the
forecast area this evening. Along the leading edge of this
moisture fetch weak convection is developing in southeast
Yellowstone county and should move into the Billings area shortly.
Radar estimates over portions of Big Horn county, where this
activity originated earlier, show mainly less than a third of an
inch of rainfall which is confirmed by a few gage reports.
However there are some patches of much heavier accumulations where
stronger slow moving cells developed from around Lodge Grass to
near Saint Xavier. Overall expect the potential for heavy rainfall
to diminish over the next few hours with sunset, but a tenth to a
third of an inch of precipitation is certainly possible in some
locations overnight as this monsoonal weather pattern continues
into tomorrow. Updated forecast for the latest precipitation
trends into Thursday along with lowering high temperatures
Thursday due to cloud and precipitation influences which are now
showing up in the models with more certainty. For those traveling
tonight (including much of I-90 in SC MT) be sure to slow down
when rain is encountered as ponding of water and poor visibility
could make conditions dangerous at times at high speeds. Chambers

&&

.DISCUSSION...

Tonight through Friday night...

Rain showers will continue for locations in the high terrain
overnight tonight. Thursday, a 500mb wave will lift into Wyoming
bringing continued precipitation chances through Saturday.
Southwest flow aloft and a surface low pressure system in Wyoming
bringing southeasterly winds will combine to create PWAT values
around 200% of normal. Weak upper level flow throughout the short
term will lead to slow moving showers and thunderstorms, which,
when combined with anomalously high moisture, will lead to heavy
rain potential. This has led WPC to issue a risk level 1 of 4 for
excessive rain for Thursday and Friday creating flooding concerns,
especially near burn scars.

Precipitation chances are expected to move off of the mountains
Thursday overspreading the region by 6 PM. Confidence in
precipitation and precipitation amounts are highest over the
Absaroka/Beartooth mountains and surrounding foothills with the
NBM giving these locations a 30-50% chance for greater than 0.5
inches of rain. The Canadian and GFS Ensembles keep precipitation
closer to the mountains with the ECMWF spreading them farther
east. Lower elevation locations west of a line from Roundup to
Alzada have a 15-40% chance of getting greater than 0.25 inches of
rain.

Uncertainty in precipitation amounts remains high Friday due to
weak forcing. Precipitation clusters show large discrepancies
with the GFS and Canadian Ensembles indicating 0.10-0.25 inches of
precipitation for far southeast Montana and little to no
precipitation elsewhere. The ECMWF Ensemble indicates widespread
precipitation amounts of 0.25-0.50. The Canadian and ECMWF
deterministic models indicate stronger low pressure systems over
the western Dakotas wrapping around large amounts of moisture,
likely indicating what a high precipitation scenario may look
like. Overall, the NBM is giving southeast Montana a 25-50% chance
of getting greater than 0.50 inches of rain for the 48 hour
period ending 6 AM Saturday. Torgerson

Saturday through Wednesday...

Some isolated to scattered showers may linger into Saturday
afternoon in eastern MT as the previously mentioned feature exits
the region. There is high confidence that this weekend will bring
back ridging across the Northern Rockies as nearly all model
solutions show higher heights throughout the region. A quasi-
cutoff low is forecast to meander off of the west coast which will
slow down the overall upper level progression. High temps are not
forecast to be anything to write home about as even the NBM 90%
values are only in the low 90s, or roughly 10F above average. All
this to day, it should be a nice labor day weekend for much of the
region with mostly warm and dry conditions.

As we will be under southwesterly flow, due to the low off the
coast, there could be some isolated showers and storms in the
mountains and foothills that would be capable of dropping a quick
0.1" of rain. Those with plans in the foothills, and especially
the mountains, should make sure they have several reliable ways
to stay up to date on the forecast.

Moving into the middle of next week a lot more uncertainty is
seen across the models. When looking at the clusters, there are
primarily two, nearly opposite, solutions that show up. The first
solution wants to dissolve the low off the coast and have the
ridge gradually retrograde. This may put parts of the CWA at risk
for scattered showers and storms due to northwest flow ushering
in vort maxes. The moisture return, however, may be lacking which
could aid in keeping areas dry. The second, slightly less favored
solution, shows the ridge slightly stronger, or not retrograding
as much allowing for the entire CWA to remain dry. Be sure to
check future forecasts if you have interests for the middle of
next week. WMR

&&

.AVIATION...

Scattered to widespread showers will continue across south
central MT, including near KLVM, KBIL, and KSHR, through the
period. Isolated to scattered thunderstorms will move in over the
west Thursday afternoon, spreading east through the evening.
Expect mountain obscuration through the period. Archer

&&

.PRELIMINARY POINT TEMP/POPS...

    Thu     Fri     Sat     Sun     Mon     Tue     Wed
-----------------------------------------------------------
BIL 061/076 059/076 056/081 055/086 057/088 057/084 055/082
    46/T    55/T    32/W    10/U    01/U    12/W    22/W
LVM 051/070 049/076 048/080 047/086 050/087 050/083 048/083
    68/T    65/T    32/W    11/U    12/W    23/T    22/T
HDN 059/079 056/076 054/080 052/086 053/088 055/084 053/081
    66/T    65/T    32/W    10/U    01/U    11/B    21/B
MLS 059/083 060/073 056/077 055/082 056/087 057/084 053/078
    01/E    44/T    42/W    10/U    00/U    11/B    21/B
4BQ 061/079 059/073 056/076 055/081 055/085 057/083 054/078
    35/T    75/T    43/W    10/U    00/U    11/B    21/U
BHK 053/082 055/072 053/076 052/080 053/084 053/081 049/075
    00/B    33/T    42/W    20/U    00/U    11/B    21/B
SHR 054/074 051/076 050/076 049/082 051/085 052/081 050/078
    47/T    76/T    44/T    11/U    01/U    12/T    22/W

&&

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

&&

$$
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