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 FXUS65 KBYZ 170549

Area Forecast Discussion...Updated
National Weather Service Billings MT
1049 PM MST Sat Dec 16 2017


Snow is rapidly decreasing across Southern Big Horn and Sheridan
Counties late this evening. Additional accumulations only around
an inch are possible. Therefore, the winter weather advisory will
be allowed to expire at 11pm. Hooley

.SHORT TERM...valid for Sun and Mon...

Snow was still ongoing across western and central areas late this
afternoon with weak ascent aloft and upslope flow still in place
near the surface. Satellite showed a clearing line approaching our
far northwest as of 3pm MST. Still expect snow to diminish from
north to south through the evening with snow lingering longest
over the Bighorn Mountains and adjacent foothill locations.
Generally an inch or less of additional snow accumulations is
expected, with a couple inches possible along the Bighorn
foothills and 2 to 4 additional inches possible in the Bighorn
Mountains. Will let the Winter Weather Advisories in effect for
our western and central zones expire as planned at 6pm as only
minor accumulations are expected after that time. Will continue
the advisories near the Bighorn Mountains through 11pm tonight.

Skies will clear out behind the departing system tonight with
temperatures dropping into the teens for most places. Will need to
monitor cold spots like Livingston and Sheridan as temperatures
down into the single digits are possible given the recent
snowfall. Wet roads will freeze this evening and overnight with
slick roads a good possibility. Patchy fog is possible late this
evening and into the overnight where precipitation fell today.
High pressure will build over the region on Sunday with lee
troughing developing over central MT. Winds will increase along
the western foothills Sunday evening as lee troughing develops
over central MT ahead of another approaching shortwave. Have gone
ahead and issued a High Wind Watch for the Livingston to Big
Timber areas as well as near Nye for Sunday evening through Monday
afternoon. Strong winds aloft and favorable surface pressure
gradients could result in winds gusting to 75 mph at Livingston
and Nye, with gusts of 55 to 65 mph near Big Timber. Showers are
possible over portions of the area on Monday as the next shortwave
moves through the region. Not expecting much accumulation with the
showers. Highs will range from the upper 30s to lower 40s on
Sunday with 40s on Monday. STP

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

Made some significant changes to the extended. Changes involve
the Wednesday through Wednesday night period and for late in the
week into next weekend.

Models bring a sharp trough into the area on Wednesday. This
trough contains significant ascent on the front side and drags a
strong front through. Raised PoPs to likelies for the frontal
passage as models have consistently painted the area with
snowfall. The EC was less aggressive in snowfall behind the front,
but the GFS was putting down almost .2 inches of liquid in the
cold air, with more along the foothills. Could see 2-4 inches of
snowfall, and possibly more along the foothills. The one drawback
for this potential snow event is the quick moving nature of the
ascent. Should be a quick hitter, and if northwest winds develop
at low levels, that would mean less snow over the central plains.
At any rate, model consistency has been such that felt raising
PoPs to likely was warranted.

The other change was to make the end of the week into next
weekend colder. A western ridge amplifies sharply off the west
coast and allows strong energy to drop toward the Great Basin by
Friday. This will send a cold front into Montana Thursday, with a
reimbursing arctic front Friday into next weekend, with a deep
trough taking shape over the northern plains. The EC was quite
chilly, with 850mb temperatures of -26c dropping into Montana by
Sunday. Lowered temperatures quite a bit for these periods. This
arctic will bring in a shot of snow too as it invades. TWH



Snow tapering off at BIL and SHR over the next few hours. Fog
impacts possible at LVM and BIL through the morning hours.
Southwest winds increase at Livingston during the early morning
with gusts to 50 kts by late afternoon and early evening Sunday.



Sun Mon Tue Wed Thu Fri Sat
BIL 018/039 030/047 028/042 031/036 010/023 015/023 010/020
60/U 12/R 32/O 37/S 71/B 12/S 32/S
LVM 010/037 033/045 033/046 034/038 008/021 014/021 009/019
31/N 24/R 33/O 47/O 61/B 22/S 32/S
HDN 017/042 027/049 025/043 027/038 009/022 015/021 010/020
20/U 12/R 42/O 37/S 71/B 12/S 32/S
MLS 019/041 029/047 024/039 025/036 007/021 014/020 008/018
00/U 12/R 22/O 37/S 71/B 12/S 31/B
4BQ 019/040 027/050 025/042 027/040 008/021 012/021 007/019
10/U 12/R 31/E 26/O 72/S 12/S 31/B
BHK 015/039 026/045 022/037 022/034 004/019 010/019 002/017
00/U 12/R 21/E 27/S 70/B 12/S 21/B
SHR 011/038 023/049 023/044 026/040 008/019 009/023 005/018
90/U 11/B 21/B 16/O 72/S 12/S 32/S


MT...High Wind Watch in effect from Sunday evening through Monday
afternoon FOR ZONES 41-65-66.