347
FXUS65 KBYZ 240003
AFDBYZ

Area Forecast Discussion...Updated
National Weather Service Billings MT
503 PM MST Sat Nov 23 2024

.KEY MESSAGES...

- Strong gusty winds along the western foothills through early
  evening.

- Turning colder with some snow at lower elevations late tonight
  into Sunday (Probabilities trending slightly upward...40-65%
  chance of 1+ inches Yellowstone County westward).

- Mostly dry Monday through Wednesday.

- Waves of snow and colder air possible Wednesday night through
  the holiday weekend, but details are very uncertain at this
  time; monitor the forecast if you have travel plans!

&&

.DISCUSSION...
Tonight through Sunday night...

Satellite imagery shows a partial clearing from the west into
portions of southern Montana ahead of a deep Pacific coast trough.

Winds...Lee side pressure falls occurring now over the eastern
plains of Montana and tightening up the pressure gradient over the
foothills. 700 mb winds are progged to reach around 45kts from
the W/SW helping to boost wind in the foothills. Gusts over 50 mph
mph will continue in the Livingston to Big Timber corridor late
today and early this evening before the frontal passage disrupts
things. As upper trough moves in from the west, we may see
a very short window of elevated W/SW wind at other foothill
locations like Red Lodge, Fort Smith and Dayton/Sheridan. Gusts of
30-40 mph gusts are possible at these locations (30-50% chance).
Then this evening, the arrival of a cold front will end the risk
of gusty winds along the foothills and introduce brisk NW winds
across the lower elevations tonight, continuing in the east thru
Sunday.

Temperature forecast for rest of today is rather convoluted. Low
level cool easterly winds will persist late today for much of the
area...but by early evening we may see a some SW-W winds push
somewhat east of the foothills, to be followed quickly by the cold
front and shift to NW winds this evening. Some locations
(including Billings and Sheridan) could see their high temps for
today occur in the early evening (after 5 pm). Sunday will be our
coldest day yet of the fall with highs remaining below freezing
across the area.

Precipitation...Height falls w/ moist SW flow will bring some
snow to the western slopes of the mountains this afternoon into
the evening, with a period of drying and subsidence tonight behind
the initial wave. Frontal precip at lower elevations should be
minimal as most of the forcing lifts to the north/northwest of our
CWA and upslope remains weak and relatively shallow in the
foothills. However, by Sunday morning the upper jet support ahead
of the main trough axis will strengthen lower level frontogenesis
and low level convergence. Cross sections indicate best lift is
through the dendritic layer across the south/central zones from
Billings to Livingston for a short time Sunday morning. Since this
forcing slides fairly quickly S/SE through the day and usplope is
shallow...snowfall accumulations should be limited. That
said...there is a chance of a narrow intense band to drop 1-3
inches somewhere, with the greatest chance along and south of a
Melville- Billings- Busby line. By late afternoon the trough axis
and forcing are pushing southeast bringing any lingering snow to an
end. Sunday night will see at least partial clearing, and set up the
coldest night of the season so far with overnight lows in the
single digits and teens.

Some of the aforementioned areas (including Billings) have yet to
see much if any accumulating snowfall. Due to the colder temps,
we should see accumulation on roads and sidewalks (not just
"grassy" areas). So we believe its prudent to highlight the risk
of accumulating snowfall even though amounts will be limited. We
have issued winter weather advisories from Livingston (and
Paradise Valley) through Billings and down into southern Big Horn
County. Valid period will be 2 AM tonight through 5 PM Sunday. The
heaviest snow should occur Sunday morning.

Here are some noteworthy probabilities thru Sunday. Please note the
chance of 1 inch or more has been trending upward for south central
sections...

1+ inches of snow:  40-70% west of Rosebud County
2+ inches of snow:  15-40% at lower elevations, 80-90% mountains
4+ inches of snow:  70% over the higher western mountains
6+ inches of snow:  25-50% over the higher western mountains

BT



Monday through Saturday...

A period of ridging will begin to build over the region, Monday.
With this pattern, dry conditions and high temperatures will be in
the upper 20s to low 30s around and east of Billings, and upper
30s to low 40s west of Billings. Temperatures will warm into the
upper 30s and low 40s on Tuesday, with a low chance (5 to 25%) from
Harlowton to Billings to Sheridan. The chance for precipitation
in the mountains and foothills is 30-60%, with an inch or two of
snowfall in the mountains.

Tuesday evening, the upper low off the West Coast will begin
coming ashore, buckling the ridge over the Northern Rockies.
Models and ensembles are slowly starting to agreement on some
elements of the weather pattern, Wednesday into the weekend.
However, there is still a large gap to be resolved, with a general
trend toward cooler temperatures, there is great uncertainty on
the extent of precipitation chances. The range for potential high
temperatures is 20-40F.

The current forecast for Thanksgiving Day has high temperatures
in the 20s to low 30sF, coldest in the east.

Continue to monitor the forecast for updates as the Holiday
approaches.

Matos
&&

.AVIATION...

Areas of MVFR/IFR ceilings with patchy fog will continue E and SE
of KMLS tonight. Elsewhere, conditions will deteriorate from W to
E to MVFR/IFR, as a cold front pushes through the area bringing
low ceilings as well as rain and snow changing to all snow late.
These conditions will persist on Sunday, especially from KLVM to
KBIL S. Gusty W surface winds will persist at KLVM to K6S0 through
06Z tonight. The mountains will be obscured much of the period.
Arthur


&&

.PRELIMINARY POINT TEMP/POPS...

    Sun     Mon     Tue     Wed     Thu     Fri     Sat
-----------------------------------------------------------
BIL 020/027 009/032 019/041 022/038 016/030 013/027 009/021
    39/S    10/B    01/B    11/B    33/J    22/J    21/E
LVM 022/034 016/042 023/043 022/038 017/036 016/035 013/031
    59/S    10/U    12/J    21/B    22/J    22/J    21/E
HDN 017/027 007/032 014/041 019/037 013/029 010/029 005/021
    28/S    10/U    01/B    22/J    44/J    23/J    32/J
MLS 016/024 006/026 012/039 015/031 010/022 005/023 002/016
    11/B    00/U    00/B    00/B    22/J    12/J    11/B
4BQ 019/026 008/032 014/043 020/036 013/027 008/029 007/021
    04/S    00/U    00/B    11/B    22/J    11/B    11/B
BHK 012/025 002/026 007/036 011/030 005/020 902/020 902/016
    01/B    00/U    00/B    10/B    11/E    11/B    11/B
SHR 019/030 009/040 016/047 020/039 014/034 011/034 007/026
    15/S    10/U    01/B    22/J    33/J    22/J    22/J

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory in effect from 2 AM to 5 PM MST
      Sunday FOR ZONES 34-65-66-138-141-169-170-235.
     Winter Weather Advisory in effect from 11 PM this evening to
      5 PM MST Sunday FOR ZONE 64.
WY...None.

&&

$$
weather.gov/billings