121
FXUS65 KBYZ 111841
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
1241 PM MDT Tue Aug 11 2026

.KEY MESSAGES...

- Significant wildfire smoke persists through Wednesday. Much
  improved conditions expected Thursday into the weekend.

- Low chances (15-30%)of afternoon thunderstorms in far southeast
  Montana today. A severe storm is possible Carter and Fallon
  Counties 1 to 5 pm.

- More widespread shower and thunderstorm chances for Wednesday.
  Low chances for severe storms southeast Montana.

- Much cooler with widespread showers and thunderstorms (40-100%
  chance) Thursday through Friday, possibly into Saturday.
  Locally heavy downpours are likely with any storms. Severe
  threat is very low.

- Warmer with a daily chance (20-50%) of thunderstorms this Sunday
  into Monday.


&&

.DISCUSSION...

Rest of Today through Monday...

Upper level pattern is pretty benign for today with zonal westerly
flow aloft and only weak energy crossing the area. Underneath that
though there is persistent southeasterly flow working into SE
Montana that will boost afternoon CAPE values to around 2000j/kg
and producing enough shear to support a chance for a few strong to
severe thunderstorms. Previous model runs kept convective
initiation just to the east of the forecast area, but the 12z runs
are further east developing convection from Fallon south into
Carter county between 1pm and 5pm. Strong winds (60-70mph) and
heavy rain will be the main threats with any storms that do
develop over this area today, with large hail being a secondary
threat. The limiting factor will be energy available to kick start
the convection as the energy aloft looks weak and mainly
streamwise which is less conducive to lifting the atmosphere. The
HRRR seems to be downplaying the western initiation and the upper
dynamics, generating initial convection over the eastern Black
Hills, which actually seems pretty reasonable. However can`t
ignore the other models, especially with a large outdoor event in
Alzada this afternoon. Wouldn`t be surprised to see the SPC 18z
outlook push the marginal/slight risk further west to cover the
latest model guidance.

The rest of the area will be war and dry with the aforementioned
westerly flow over the area suppressing convection. Smoke
concentrations look to increase this afternoon over the western
half of the forecast area as the HRRR is advecting in significant
smoke from the fires in SW Montana today. Highs this afternoon
will be mainly in the low to mid 90s. Overnight lows will be in
the 60s for much of the area thanks to the smoke holding in the
heat. Western valley locations will drop into the mid 50s.

Set up for Wednesday looks similar to today, with the exception of
a stronger upper disturbance arriving early afternoon from the
southwest, crossing areas from Big Horn/Sheridan County northeast
through Fallon County. This will bring a more widespread threat
for convection, however the shear and CAPE will both be weaker, so
less of a threat for strong to severe storms. Best chance for a
stronger storm or two will remain over the SE Montana. PWAT values
increase Wednesday with higher values pushing further west.
Combined with weaker shear/storm motion the potential for locally
heavy rainfall with any storms is enhances. WPC has issued a
marginal risk for excessive rainfall (Flash Flood potential) for
the eastern 3/4 of the forecast area Wednesday to cover this
increase in available moisture.

Persistent east-southeast low level winds will continue to
advect low level moisture into the area Thursday/Friday while
monsoonal moisture increases aloft. This will produce a very juicy
atmosphere over the area for this time of year. Southwest flow
will be over the area during this period with occasional
disturbances crossing us, providing lift for more widespread
shower and thunderstorm activity. It won`t take much to kick off
precipitation given the amount of water in the atmosphere (3 to 4
standard deviations above normal) during this period. GEFS
precipitation percentiles are showing forecast precipitation
amounts in the 95th to 99th percentile for the eastern 2/3 of the
forecast area Thursday into Friday, so climatically this is a high
end precipitation event being forecast by the models. WPC
probabilities for half an inch or more precipitation shows
widespread 50-100% chances across the forecast area Thu- Fri, with
probabilities for 1+ inches above 50% from Rosebud County east
into the Dakotas. WPC has a slight risk for excessive rainfall
(flash flood potential) from a Roundup to Billings line eastward
for Thursday into Friday morning. With the precipitation and cloud
cover, along with a general north/northeast wind, will see
temperatures drop well below normal for Thu/Fri, with highs
expected in the 70s both days.

Saturday has the potential to remain unsettled and cool, but some
models are starting a warming and drying trend Saturday. For now
the NBM is leaning cool and unsettled and the official forecast
reflects that, but wouldn`t be surprised to see this period trend
warmer and drier as southerly winds take hold.

Sunday into Monday shows a ridge bulging northward along the spine
of the Rockies into our vicinity, thanks to a persistent and at
times digging upper trof just off the west coast. This should
bring temperatures back toward seasonal levels and decrease
precipitation chances. That said, depending on how much rain falls
Thu-Sat, there may be plenty of residual moisture to support at
least decent afternoon and evening precipitation chances each day.
Chambers

.AVIATION...

Wildfire smoke will continue to impact the region over the next
24 hours. Slant range visibility will be reduced. Slight
reductions in surface visibility are possible. The TAF sites most
likely to be impacted are KLVM, KSHR, and KBIL. Smoke is unlikely
to cause reductions in flight category. Scattered showers and
thunderstorms from Rosebud County and east are expected Wednesday
morning before increasing through the afternoon. Heavy rain could
lead to MVFR conditions. Torgerson

&&

.PRELIMINARY POINT TEMP/POPS...

    Wed     Thu     Fri     Sat     Sun     Mon     Tue
-----------------------------------------------------------
BIL 064/085 061/075 059/074 055/077 055/084 058/088 059/086
    00/K    76/T    97/T    63/T    41/U    21/B    32/W
LVM 055/086 052/074 050/073 045/076 045/083 049/085 050/083
    01/K    66/T    99/T    87/T    52/T    32/T    33/T
HDN 062/088 058/079 056/076 050/079 051/086 054/090 055/088
    02/W    67/T    95/T    63/T    41/U    21/B    22/W
MLS 063/085 060/076 059/077 052/077 053/084 057/089 059/088
    15/T    58/T    +5/T    23/W    31/B    22/T    22/W
4BQ 065/087 061/076 060/077 055/077 055/083 058/088 060/088
    05/T    58/T    +4/T    43/T    42/T    21/B    31/B
BHK 057/083 054/073 055/077 048/077 048/082 052/087 055/088
    25/T    67/T    +7/T    21/B    12/T    22/W    32/T
SHR 060/086 056/076 055/074 050/075 048/081 050/086 053/085
    02/T    49/T    99/T    87/T    51/U    11/B    12/T

&&

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

&&

$$
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