Area Forecast Discussion
Issued by NWS Billings, MT

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532
FXUS65 KBYZ 210826
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
226 AM MDT Wed May 21 2025

.KEY MESSAGES...

- Breezy with isolated showers today; dry late tonight and
  Thursday morning, with patchy fog in southeast Montana.

- Periodic showers, a few afternoon and evening thunderstorms, and
  seasonable temps from late Thursday to Sunday.

- Memorial Day Forecast: Slight (20%) chance of showers and
  thunderstorms; high temps in the mid 60s to mid 70s (coolest
  east).

- Temps back to near 80 degrees toward the middle of next week.

&&

.DISCUSSION...
Today through Thursday Night...

Satellite imagery shows WNW flow aloft with an upper level jet to
our south from OR to southwest WY. There is a weak shortwave
moving thru south central MT, which with steep mid level lapse
rates is producing showers over/near the Beartooth Absarokas as of
0730z. As this wave tracks to the ESE the rain and mountain snow
showers will do likewise thru the remainder of the night...likely
staying to the south of Billings. There are also a couple of
showers dropping thru eastern Powder River along an axis of low
level frontogenesis, and these should exit southeast MT over the
next couple hours. Light easterly winds persist in our far east
and in this area there is still a risk of localized fog from now
thru ~14z.

Once the south central MT wave exits to the east, we will undergo
gradual height rises associated with a low amplitude ridge to our
west. With this in mind, shower potential will be lower today and
anchored mainly over our southern mountains. Low level
frontogenesis will again be a potential axis of showers and weak
t-storms this afternoon from Miles City to Broadus eastward.
Elsewhere, it will be drier with mixed/breezy downslope winds
(gusts 20-30 mph). Look for high temps in the mid 50s to mid 60s,
again coolest near the Dakotas border.

Flat ridging will bring a period of dry weather tonight thru
midday Thursday. Boundary layer in our far east looks to remain
moist enough for another risk of fog late tonight thru early
Thursday east of Forsyth and Broadus.

Surface winds turn easterly Thursday and the ridging should push
temps to the mid 60s to lower 70s (the warmest day for about a
week). Next Pacific shortwave will introduce height falls and a
chance of convection by afternoon in the west. Showers w/ embedded
weak t-storms are likely from west to east with the trof passage
Thursday night. There will be a bit of plains moisture return
ahead of this wave, but the flow is too progressive to allow
enough moisture/instability for any risk of strong storms. Current
HREF shows sbcapes of 200-400 j/kg. Regarding precip, though
there remains a fair amount of model uncertainty, most areas
should see 0.15" or less. The probability of exceeding 0.20" is
35-45% in our NW and NE, to less than 10% in Sheridan County.

JKL

Friday through Tuesday...

Potential for showers and weak t-storms will continue each day
Friday through Sunday, as another trof moves slowly thru the
region. Ascent generally looks to remain weak and the precip will
be more diurnally driven than not, but there is model uncertainty
regarding the depth of the trof. As a result, there is
considerable ensemble spread in QPF during this time. A higher
amplitude trof would obviously be wetter, but this won`t be rain-
maker of the magnitude of the past few days. The probability of
exceeding 0.50" from Friday to early Sunday ranges from about 10%
in the north to 45% in the south. Sheridan has a 20% chance of
reaching an inch of precip. Upslope areas in our south should pick
up greatest amounts as flow turns northwesterly by Saturday
(which seems to be the wettest and coolest day). Temps will cool
back to the 60s Friday and Saturday. Snow levels in the high
country look to set up around 9kft, so keep this in mind if you
are planning to head for the mountains over Memorial Day weekend.

There is growing confidence for a building ridge early next week,
which would bring warmer & drier weather. A potential fly in the
ointment is if the ridge axis stays to our west and cyclonic
northerly flow remains over the northern plains...a set up which
would keep "cooler" easterly winds for southeast MT and northern
WY. For now, look for near 70F in the west Sunday, followed by
mid 60s to mid 70s Monday, and 70s to lower 80s Tuesday. Cannot
completely rule out some mainly diurnal mountain showers on these
days. The warmer temps will also increase high elevation snow melt
again, but our rivers are currently in good shape and can take
some water.

JKL

&&

.AVIATION...

There is a risk of fog & stratus (30% chance) near the Dakotas
border (affecting KBHK-K97M) from now through ~14z this morning.
The remainder of the area will see VFR, but an early morning
disturbance is bringing scattered rain and mountain snow showers
to southern areas...so expect mountain obscurations and perhaps
local MVFR near the foothills. VFR will otherwise prevail today
and tonight with only isolated afternoon and evening showers. KMLS
& KBHK could see an isolated TS nearby (<20% chance) between
21-06Z. Late tonight, localized fog is possible again in far
southeast east of Rosebud County. JKL

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Thu     Fri     Sat     Sun     Mon     Tue
-------------------------------------------------------
BIL 064 041/071 046/069 046/063 046/070 046/075 050/080
    1/U 02/W    53/W    36/T    22/T    01/U    12/T
LVM 061 036/065 040/067 043/062 041/071 045/077 048/079
    1/B 06/T    65/W    46/T    21/U    12/T    23/T
HDN 064 039/071 046/069 046/064 044/068 044/074 048/080
    1/U 01/B    63/W    46/T    33/T    11/U    12/W
MLS 064 038/070 048/067 045/064 045/066 044/072 047/078
    2/T 10/U    84/W    35/T    33/T    11/U    11/U
4BQ 062 038/068 046/069 046/061 045/063 043/069 046/076
    1/U 10/U    62/T    46/T    44/T    11/U    11/U
BHK 056 032/064 043/061 041/059 042/061 040/066 042/071
    2/T 10/U    74/W    34/T    44/T    11/U    11/U
SHR 061 035/070 042/069 044/060 041/064 041/071 044/077
    3/W 11/B    43/T    58/T    44/T    12/T    12/T

&&

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

&&

$$
weather.gov/billings