682
FXUS65 KBYZ 210831
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
231 AM MDT Tue May 21 2024

.DISCUSSION...

Today through Wednesday night...

Upper level low continues to slowly move east across the northern
half of Wyoming early this morning, with an enhanced baroclinic
leaf showing on satellite over central sections of southern
Montana/northern Wyoming. Overall this system is looking less
impressive than previously advertised with a system ejecting out
of the 4 corners pulling energy out of it, and the parent low over
southern Canada pushing northwesterly flow further to the south
shunting the track a bit further south and funneling dryer air
into the area. The result is that precipitation with this system
is being confined to the Bighorn mountains and nearby lower
elevations today. As a result have cancelled the Winter Storm
Warning for the southwest mountains and the northern Bighorn/Pryor
mountains. Still expect to see an additional 4 to 8 inches of
snow through this afternoon for the area remaining in the Winter
Storm Warning. NBM probabilities for over 10 inches of additional
snow are around 40 percent for Bighorn mountain locations along
the Johnson/Sheridan count line.

With winds shifting out of the west- northwest today will see
temperatures warming back into the low to mid 60s this afternoon.
With the upper trof over the area, isolated to scattered
instability showers can be expected over most areas, from this
afternoon into the early evening hours. Precipitation with this
activity should be under a tenth of an inch for most areas.
Locations along I-90 south of Crow Agency have a better than 50%
chance for more than a quarter of an inch of precipitation through
this evening, including Sheridan Wyoming.

Zonal flow to weak ridging will be over the area tonight through
Wednesday morning, for dry conditions. Temperatures will drop into
the 30s in many locations tonight with the potential for frost
development. Take precautions to protect tender vegitation
tonight.

Next storm system moves quickly from near Seattle Wednesday
morning to SE Idaho by Thursday morning. The latest deterministic
model runs have come into good agreement with the timing and the
track of the system through Wednesday night. Left front jet
divergence moves into western zones late in the afternoon and
spreads eastward overnight. Winds turn easterly during this same
time frame, enhancing upslope lift. The combination of the two
will see good chances (40-70%) of precipitation spreading west to
east across the area Wednesday night. Snow levels drop from 8500
feet to 6500 feet Wednesday night. NBM snow totals Wednesday night
currently range from 2 to 10 inches, heaviest in the Crazy
mountains. Issued a Winter Storm Watch for the western mountain
zones (Beartooth/Absaroka/Crazy mountains) starting at 6pm
Wednesday evening going through Thursday evening. Chambers

Thursday through Tuesday...

Model agreement continues to support widespread precipitation,
including mountain snow, for Thursday into early Friday. The
latest NBM probabilities have a 55-85% chance (lowest over the
east) of at least 0.25" through Friday and a 35-65% chance (lowest
over the east) of over 0.5". For the mountains, this translates
to a 60% chance of at least 6 inches of snow.

Then, late Friday into early Saturday, shortwave ridging is
expected to build in, bringing a brief period of drying and warmer
temperatures to Saturday. Another low will move in late Saturday
into early Sunday, and potentially linger through early Monday
before ridging builds back over the region. Currently, Saturday
and Sunday each have a 30-50% chance (lowest over the east) of
precip over the plains and a 50-70% chance over the mountains and
foothills. Then, as the ridge builds in, conditions are expected
to become warmer and dry.

High temperatures will be in the 50s to mid 60s through Friday,
increasing to mid 60s to low 70s for Saturday. Sunday will drop
back into the 60s before a warming trend begins, bringing back
highs into the mid 60s to low 70s Monday and into the 70s to near
80 Tuesday. Archer

&&

.AVIATION...

Isolated to scattered showers and isolated thunderstorms are
possible near all TAF sites through this evening. Areas of heavy
rain will periodically reduce conditions to MVFR/IFR. Expect
mountain obscuration. Archer

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Wed     Thu     Fri     Sat     Sun     Mon
-------------------------------------------------------
BIL 063 042/067 043/050 036/064 042/071 044/063 043/072
    3/T 22/R    79/T    52/R    13/R    55/T    32/R
LVM 060 038/060 038/048 033/062 040/065 037/060 038/071
    3/T 16/T    9+/T    32/T    15/T    65/R    22/R
HDN 063 038/070 044/054 035/065 039/073 044/066 042/073
    3/T 21/B    59/T    62/R    12/R    55/T    32/R
MLS 063 041/070 045/056 035/061 040/072 045/066 045/071
    1/B 21/B    38/T    62/R    11/B    44/T    32/R
4BQ 062 040/070 044/062 036/062 039/073 045/066 044/068
    3/T 20/U    27/T    72/R    11/B    34/T    32/R
BHK 063 037/069 042/059 034/058 037/071 042/065 042/068
    1/B 11/B    17/T    72/R    01/U    34/R    33/R
SHR 057 035/066 040/057 033/062 037/071 039/064 040/070
    7/T 21/B    48/T    62/R    12/R    45/T    33/R

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Watch in effect from Wednesday evening through
      Thursday evening FOR ZONES 67-68.
WY...Winter Storm Warning in effect until 6 PM MDT this evening
      FOR ZONE 198.

&&

$$
weather.gov/billings