Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 101025
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
325 AM MST Mon Dec 10 2018

.SHORT TERM...valid for Tdy and Tue...

Surface pressure gradient from Idaho Falls to Lewistown has
tightened to 15 mb overnight, and winds responded at Livingston
with a gust to 50 mph. Guidance indicates that the strongest
gradient will be very early this morning and expect a slackening
up through the morning hours. This should translate into the
strongest winds at Livingston and Nye very early this morning,
with a gradual decreasing trend through mid to late morning.
Another round of wind, this much stronger, expected Tuesday night
into Wednesday.

Surface pressure really tightens up Tuesday night and 700 mb
winds increase to 55 kts. Wind gusts in excess of 60 mph seems
like a sure bet Tuesday night through around noon Wednesday, with
some gusts possibly getting as high as 70 mph. Latest guidance has
shown a bump up in possible high wind criteria being hit at
Livingston (gust to 75 mph). This upward trend toward warning
criteria has been gradual, but steady. Event certainly looks like
at least a high end Advisory, with the possibility of Warning.
Will issue a High Wind Watch for the Livingston area and the
Beartooth Foothills for Tuesday night through early Wednesday
afternoon.

Otherwise, a splitting trough rolls through southern Montana and
northern Wyoming Tuesday night. This will provide decent QG
forcing with some weak instability. System has been splitting a
little more of late, and it appears the forecast area will be
right between the two stronger pieces of energy of the split. That
being said, QG forcing is modestly strong, so will maintain the
low PoPs in the forecast. Mountains will get the best shot of snow
showers, but the quick moving nature of the trough will keep
accumulations down to an inch or two.

Temperatures will be mild with downslope flow. Clouds will help
to temper the warmup for central and western zones, with snow on
the ground over the east keeping highs down there. TWH

.LONG TERM...valid for Wed...Thu...Fri...Sat...Sun...

Relatively minor changes to the extended forecast period, as
winds continue to be the main concern through the extended
forecast period, especially for gap flow prone areas.

Reasonably good model agreement and local guidance points to a
the period of gusty winds in gap flow areas, including
Livingston, Nye, and Big Timber to continue into Friday night.
That said, there will certainly be periods of lesser winds,
associated with disturbances crossing the region. Strongest
periods of winds continue to be into Wednesday morning, and
Thursday through Friday.

On Wednesday and into Wednesday night, gap winds will taper off
from those seen early in the morning, but gusty winds will spread
out onto the plains, as mixing and subsidence drive the winds to
the surface behind a departing trof. Winds continue to decrease
from West to East as trof proceeds eastward. Gap winds redevelop
early Thursday morning, with gusts quickly climbing to around 60
mph. Potential for these Advisory strength winds persist
into Friday night based on the GFS model. Winds taper off through
the weekend, but continue to remain breezy into early next week.

AS for precipitation, a progressive flow will bring a trof across
the area Wednesday, followed by a large ridge, then another trof
in the Friday night/Saturday time frame. Each trof will bring a
chance of precipitation, with best for accumulations on Wednesday,
with a mix of rain and snow. That said, precipitation amounts
should be fairly low. Only isolated showers are expected with the
Friday night/Saturday wave.

Temperatures will be in the mid 30s to upper 40s through the
extended period, with a warming trend through Friday and a few
locations seeing 50 degrees. Slightly lower temperatures are
expected on Saturday behind the trof, with a gradual warming trend
through the remainder of the period. Gilstad

&&

.AVIATION...

Expect southwesterly surface winds to gust up to 45 kts at KLVM,
and 30 kts at KBIL this morning to slowly taper off through this
afternoon.

VFR conditions will persist through the day, under increasingly
cloudy skies. Scattered snow showers will bring localized MVFR to
IFR conditions across South Central and Southeastern Montana and
North Central Wyoming overnight. Gilstad

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Tue     Wed     Thu     Fri     Sat     Sun
-------------------------------------------------------
BIL 044 027/043 028/044 025/043 029/048 031/045 024/043
    0/N 31/B    12/J    20/N    00/B    01/B    00/U
LVM 042 024/039 028/039 020/038 025/045 028/039 021/040
    0/N 31/N    34/W    21/N    10/N    12/J    11/N
HDN 044 021/043 023/044 021/044 024/050 026/046 020/044
    0/B 22/J    12/W    20/N    00/B    01/B    00/U
MLS 037 019/036 022/041 021/039 023/042 025/041 019/036
    0/B 11/B    13/W    20/B    10/U    11/B    00/U
4BQ 038 019/038 021/041 022/039 023/044 026/043 019/038
    0/B 13/J    13/W    30/N    10/U    12/J    00/U
BHK 037 022/036 022/041 022/038 024/043 026/041 019/036
    0/B 02/J    13/W    20/N    10/U    12/J    00/U
SHR 046 022/041 020/043 018/043 021/049 025/044 019/042
    0/B 13/J    13/W    20/N    00/U    01/B    00/U

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...High Wind Watch in effect from Tuesday evening through
      Wednesday afternoon FOR ZONES 65-66.
WY...None.

&&

$$
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