Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 161102
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
402 AM MST Sat Dec 16 2017

.SHORT TERM...valid for Tdy and Sun...

The cold front has moved through the entire forecast area as of
early this morning. Current obs upstream have not been that cold
as most locations through last evening into early this morning
have been in the upper 30s to lower 40s. However, temperatures
just the past 90 minutes or so have dropped into the lower and
middle 30s. Winds have switched to the northeast for most areas
except Livingston. An upper trough and area of vorticity currently
over southern Idaho will move east during the day. Synoptic
forcing, decent instability and steep lapse rates today will
result in light to moderate snowfall today along and west of a
Roundup- Billings- Sheridan line. Radar the past few hours has
been filling in across the central and western areas with movement
north to south. Precip started as rain for a couple of hours but
has recently changed over to snow. Temperatures are not expected
to fall below freezing for the remainder of tonight into the day
Saturday so accumulations but be difficult to achieve on road
surfaces. However, with steep lapse rates, any bursts of heavier
snowfall will be enough to help accumulate on paved surfaces. The
current winter weather advisories from Golden Valley County
southeast to Sheridan County and points west still look good where
2 to 4 inches will be likely with slightly higher amounts for the
foothills. As a result, we will make no changes to the advisories
with this forecast issuance. The snow will slowly taper off from
north to south during the afternoon and is expected to be out of
the area by this evening.

Ridging, as well as lee-side troughing will build back once again
on Sunday and Sunday night. Models show very tight pressure
gradients across the Upper Yellowstone and Stillwater Valleys by
Sunday night into Monday morning. Gradient orientation will be
more east/west at first and favoring Big Timber and Harlowton but
will become more north/south favoring the Livingston area Sunday
night. Confidence is very high for advisory winds with the
possibility of warning criteria. As a result, I did increase wind
gusts for the Sunday night period. In addition, given the winds,
overnight lows for Sunday night/Monday morning were raised quite a
bit from Nye to Livingston as temperatures may not drop below
freezing. Hooley

.LONG TERM...valid for Mon...Tue...Wed...Thu...Fri...

Strong gap flow winds Monday morning will be subsiding as a cold
front moves through the area. Precipitation will slide into the
area behind the front but the window for this precipitation looks
short as heights begin to rise Monday evening. Another round of
potential high winds arrive Tuesday evening and they end
Wednesday as a strong cold front moves into the area. This cold
front will begin the onset of a different weather regime with
below normal temperatures likely with snow falling and sticking on
the ground Wednesday afternoon and Wednesday night. Cold persists
into Thursday but this will be followed by moderation by next
weekend. However...the downsloping pattern looks like a klondike
chinook so moderation will be only into the lower 30s at best.
Even the ECMWF...which was hinting at less amplitude to the
eastern Pacific ridge driving this change is still a colder
solution this run. borsum

&&

.AVIATION...

Areas of MVFR to IFR conditions with local LIFR as snow and fog
develop across the area on upslope conditions. Expect foothill and
mountain obscurations through the period. The main band of
precipitation will move southward this morning with some clearing
expected at KMLS and KBIL this afternoon. borsum

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Sun     Mon     Tue     Wed     Thu     Fri
-------------------------------------------------------
BIL 035 018/038 031/046 028/042 033/038 012/027 016/031
    9/S 20/U    23/O    32/O    36/O    41/B    12/S
LVM 032 015/037 033/042 032/046 036/040 010/024 015/028
    8/S 21/N    25/O    43/O    46/O    42/S    12/S
HDN 036 017/039 026/047 024/043 029/040 011/027 016/032
    8/S 10/U    14/O    32/O    36/O    52/S    13/S
MLS 038 019/038 027/045 023/039 027/038 009/023 015/029
    2/S 10/U    13/O    22/O    45/O    41/B    12/S
4BQ 036 020/038 026/047 023/042 029/042 010/024 013/030
    5/S 10/B    13/O    21/E    25/O    62/S    12/S
BHK 035 015/038 026/042 021/037 024/036 006/018 011/024
    1/E 00/U    13/O    21/E    35/O    52/S    12/S
SHR 033 014/037 023/047 023/044 028/042 010/024 010/031
    +/S 40/U    12/O    21/B    15/O    62/S    12/S

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory in effect until 6 PM MST this evening
      FOR ZONES 28-34-35-39>42-56-57-63>66.
     Winter Weather Advisory in effect until 11 PM MST this
      evening FOR ZONE 38.
WY...Winter Weather Advisory in effect until 11 PM MST this
      evening FOR ZONES 98-99.

&&

$$
weather.gov/billings



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