929
FXUS65 KBYZ 180334
AFDBYZ

Area Forecast Discussion...Updated
National Weather Service Billings MT
934 PM MDT Mon Jun 17 2024

.UPDATE...

A few strong to severe thunderstorms developed over southeast MT
this evening, but since have moved east into the Dakotas. The
Severe Thunderstorm Watch has been cancelled. Widespread showers
are moving into the region as an upper trough and associated low,
currently centered near West Yellowstone move into the region.
Expect periods of showers and mountain snow to continue to affect
the area tonight into Tuesday. Temperatures will be cool enough
that snow could mix down into the foothills locations at times,
although most accumulations should be above 6000 feet. Have
adjusted PoPs to latest trends and updated them through the
overnight. Otherwise, the rest of the forecast remains on track.
STP

&&

.DISCUSSION...

Rest of Today through Tuesday night...

Strong upper trough with unseasonably cool air will be tracking
across our region in the short term period. This will bring a
variety of weather to the area with snow in the high country and
strong to severe thunderstorms in our east.

At this time...satellite imagery showed the upper trough axis
moving through Idaho with strong S/SW mid level flow over our
area. Showers were noted on radar across our far western mountains
and nearby foothills. Cooling tops were noted across
northern/central Wyoming moving moving northeast toward our area.
where a low level convergent area had developed in relation to
the surface low centered in Wyoming. The probability of MUCAPE
and bulk shear above 30kts was greatest in this location (Rosebud
County to Sheridan County, WY). CAM`s suggest rapid
intensification of convection in this area late today with decent
helicity track signals. Shear proggs range from 45-75 kts, which
the high end could actually be too strong for deep convection, but
for now we suspect scattered strong storms in our east late today
through early evening. A few storms could be severe (damaging
wind, large hail). Storms should be moving fast so folks need to
remain alert. Showers and thunderstorms are also possible in the
west with snow levels dropping to about 8500 ft late. Areas around
Billings have about 30% chance of showers/thundershowers.

Upper trough tracks right over us tonight. Look for the stronger
convection in the east to exit into the Dakotas after 9 pm...but
showers and embedded thundershowers will increase over our CWA
(60-90% PoPs). Due to aggressive dynamic cooling with this system,
we have dropped snow levels down to around 5900 ft overnight
placing a solid mix of rain/snow in our higher foothills,
including Red Lodge. We dont expect much accumulation this low,
but would not be surprised if there is an inch of accumulation on
natural surfaces while roads remain wet. The chance of an inch in
Red Lodge is estimated to be around 35%. We are looking for about
2-4 inches accumulation on the Beartooth Pass tonight into
Tuesday.

For Tuesday...Trough axis is over Custer/Powder River Counties
around midday, then shifts to the Dakotas by evening.
Bulk of heavier precipitation is from east central Montana
northward during the day, but there is indications of some wrap
around and instability showers into our western zones in the
afternoon. Beartooth Pass could see additional accumulations
during this time. Blustery north/northwest winds 15-25 mph are a
good bet at most locations tomorrow. Precipitation winds down in
the evening as westerly flow replaces the trough.

Precipitation...Anywhere from 0.15 to 1 inch of precipitation
(rainfall and melted snowfall) can be expected with the highest
amounts generally north of Billings. Locally higher amounts are
possible in the western mountains and under thunderstorms across
the east. Probability of at least 0.25 of an inch ranges from 20%
over our southern border to 90% near the Snowies (60% at
Billings).

As far as snow goes, accumulations can generally be expected
above 7000 ft. Chances of 4 or more inches of snow in the higher
terrain of the Crazy and Beartooth/Absaroka Mountains is high.
Along the Beartooth Highway, 2-4 inches of snow can be expect.
This will create slick and wintry road conditions this evening
through Tuesday.

Lows tonight will range from mid 30s west to upper 40s east.
Temperatures on Tuesday will warm into the 50s to lower 60s.
BT


Wednesday through Monday...

For Wednesday, trailing energy from cyclonic flow in Canada will
bring increased precip chances for the mountains and SE MT
(15-30%). Southwest flow and troughing over the Pacific NW will
allow for continued chances of precip (20-40%) into Thursday.
Shortwave troughing will move east into MT Friday and Saturday
bringing more widespread chances of rain to the region. A strong
push of Gulf moisture will allow for PWATs over an inch for most
of the region (highest for eastern MT). Afternoon instability will
allow for some thunderstorms to form, but MUCAPE values generally
remain low (less than 750 J/kg), so just some general
thunderstorms are expected at this time. The best chances for at
least a half an inch of rain with this system (Fri.-Sat.) is
generally Billings east with a 20-40% chance. By Sunday, ensembles
have ridging building back in for Sunday with another potential
system entering MT Monday.

High temperatures will be in the 70s to low 80s, warming to the
upper 80s to low 90s for Sunday and Monday. TS

&&

.AVIATION...

Widespread showers and isolated thunderstorms will continue to
move through the area overnight producing MVFR to IFR conditions.
Mountains will be obscured due to snow. Conditions will begin to
improve late Tuesday morning as showers become more isolated in
coverage. STP

&&

.PRELIMINARY POINT TEMP/POPS...

    Tue     Wed     Thu     Fri     Sat     Sun     Mon
-----------------------------------------------------------
BIL 043/059 041/072 050/079 056/075 056/083 058/091 060/090
    +6/T    21/U    01/B    25/T    52/T    11/U    11/U
LVM 034/059 034/069 041/076 047/075 049/083 052/091 054/087
    95/T    22/T    01/B    15/T    42/T    11/U    11/N
HDN 041/059 036/076 048/081 055/077 054/082 054/093 058/090
    86/T    21/U    11/B    35/T    63/T    11/U    11/U
MLS 043/056 039/073 050/079 056/076 055/080 056/089 061/087
    96/W    21/U    12/T    45/T    63/T    10/U    11/U
4BQ 044/058 038/072 051/079 057/078 057/080 056/090 061/090
    83/W    12/W    12/T    45/T    63/T    11/U    11/U
BHK 045/056 036/071 048/076 054/075 054/079 053/086 056/087
    85/W    21/U    11/B    45/T    64/T    11/U    11/U
SHR 039/059 034/073 045/079 052/077 052/081 052/091 057/090
    72/T    11/U    12/T    36/T    53/T    11/U    11/U

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory remains in effect until 6 PM MDT
      Tuesday FOR ZONE 67.
WY...None.

&&

$$
weather.gov/billings