449
FXUS65 KBYZ 121851
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
1251 PM MDT Wed Aug 12 2026

.KEY MESSAGES...

- Widespread precipitation is forecast from this afternoon through
  Saturday. Locally heavy rainfall is possible during this period,
  with a slight risk of exceeding flood guidance for areas east
  of a Roundup to Billings to Sheridan line.

- Temperatures will drop well below normal Thursday through
  Saturday, and possibly Sunday.

- Air quality will drastically improve for the end of the work
  week.

&&

.DISCUSSION...

Rest of Today through Tuesday...

Zonal flow aloft with an embedded shortwave moving northeast from
NW Wyoming today. This pattern will bring widespread showers and a
few potentially strong storms to SE Montana, but mainly dry
conditions to the western half of the forecast area this
afternoon. As to the severe threat, its a short window this
afternoon, and not as good a set up as yesterday. However there is
still some good CAPE (~1500-2500j/kg) and decent shear (~40kts)
for the few hours this afternoon. Heavy rain, strong wind gusts,
and large hail are the main threats with any storms. The strong
wind threat really looks confined to the heavy precipitation
cores, but could reach 70 mph in those cores.

The shortwave shifts east this evening diminishing convection over
the east. Another wave moves in from the west mid-evening and will
provide the impetus for additional showers/thunderstorms
overnight, spreading west to east through the night. Severe threat
looks minimal with this activity, but thunder could certainly
disrupt sleep tonight.

Another break develops in the morning as the overnight shortwave
exits northeast. Another wave arrives Thursday afternoon in a
similar fashion to this afternoons, impacting mainly the eastern
half of the forecast area. While a few thunderstorms are expected
tomorrow, the threat of severe weather is near zero. Additional
energy arrives over the western and central portions of the
forecast area Thursday night, though there is still some
uncertainty in the models with strength, location and timing of
this period of precipitation. The current NBM is showing high
precipitation potential (>50%) for most of the area overnight
through Friday morning.

With the pattern aloft becoming more and more southwesterly as a
deepening trof takes hold along the west coast of the United
States, waves of energy will continue to flow over the area Friday
afternoon/night and probably will persist into Saturday. This is
reflected in the forecast with continued widespread precipitation
chances (30-60%) going into the weekend.

Monsoonal moisture will ride the increasingly southwesterly flow
aloft into the area over the next several days, tapering off (but
not completely going away) by late Saturday into Sunday. At the
same time will continue to bring low level moisture into the area
from the plains, with a strong surge Thursday into Thursday night.
The combination of moisture fetches will boost Precipitable water
values well above normal (3-4 standard deviations) Thursday into
Friday. This has prompted an Excessive Rainfall Outlook Slight
Risk to be issued by WPC for the eastern half of the forecast area
during this period, and a Marginal Risk this afternoon through
Friday for most other locations. This risk equates to the
potential to exceed flash flood guidance and produce flooding. At
this time the 1-3 hour flash flood guidance for most of the area
is between 1.5 and 3 inches due to the lack of precipitation over
the past few weeks. So, not planning any flash flood watches at
this time since the forecast precipitation in the 1 to 6 hour time
frames don`t look to exceed flood guidance at this time. In fact
WPC probabilities for exceeding 2 inches of precipitation today
through Saturday morning peak around 30-40% over NE Custer into
Northern Fallon counties with the majority of the area under 20%.
However will continue to monitor the threat closely as each wave
of precipitation impacts the area. Bottom line we are looking at a
period of beneficial rainfall over the next several days, and
through heavy downpours are likely at times, the potential for
flooding remains low (slight risk east of a Roundup to Billings to
Sheridan WY).

Temperatures will be 5 to 10 degrees cooler this afternoon
compared to Tuesday, mainly due to cloud cover and shower
activity. However the shift to northerly winds is helping as well
as the source air is from a cooler region. The cooling trend
continues into the weekend with forecast highs in the 70s for most
locations through Saturday.

For the late weekend into early next week the pattern aloft shows
a persistent trof along the west coast with southwesterly flow
over our region. There is some westward sagging of the trof though
that allows weak ridging to push into the area. This will
diminish the stronger precipitation chances to start the week as
well as allowing temperatures to rebound back toward seasonal
levels. this pattern still favors chances for precipitation,
especially the afternoon and evening showers/thunderstorm variety.
It looks like the hot/dry/smokey pattern is gone through at least
the middle of next week. Chambers

.AVIATION...

18z Discussion...

Several rounds of showers and thunderstorms will continue through
the period region-wide. The greatest risk for strong storms is
between 20z and 02z for KMLS/KBHK. While VCSH is included in the
KBIL TAF for much of the period, the greatest chances of TSRA is
between 01z and 07z. IFR conditions should be expected in all
showers and thunderstorms.

After 00z widespread MVFR CIGs develop across the region.
Localized IFR CIGs are possible at any site but due to the low
confidence it was not included in any TAF. MVFR CIGs will
persist into the day Thursday but they were raised slightly in
the TAFs after sunrise due to lower confidence.

Wildfire smoke/haze will linger across the region as well. In
conjunction with the multiple cloud decks, expect reductions to
slant range visibility. Partial to full mountain obscuration is
expected through the entire period. WMR

&&

.PRELIMINARY POINT TEMP/POPS...

    Thu     Fri     Sat     Sun     Mon     Tue     Wed
-----------------------------------------------------------
BIL 060/076 059/072 055/076 056/082 057/085 058/085 059/084
    65/T    77/T    72/T    41/B    32/W    41/B    21/B
LVM 050/075 049/071 045/076 045/081 047/082 048/082 049/082
    64/T    89/T    87/T    62/T    23/T    52/T    33/T
HDN 057/079 054/074 051/078 051/083 052/086 054/086 054/086
    66/T    76/T    64/T    42/W    21/B    41/B    22/W
MLS 057/079 057/074 053/077 053/082 055/086 057/086 058/086
    57/T    85/T    33/W    23/T    21/B    41/B    32/W
4BQ 059/080 059/075 056/076 055/081 056/085 058/085 058/086
    48/T    94/T    63/T    34/T    22/T    52/T    22/T
BHK 052/077 054/074 049/075 048/080 051/084 053/083 053/085
    55/T    88/T    21/E    13/W    31/U    42/T    32/T
SHR 054/079 053/073 051/073 049/079 049/082 051/082 051/084
    38/T    87/T    89/T    62/T    21/U    32/T    12/T

&&

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

&&

$$
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