Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 101737
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1035 AM MST Mon Dec 10 2018

Updated Aviation Section.

.UPDATE...
Made some updates within the first 24 hours of the forecast, which
includes the timing of the snowfall across Southwest MT and gusty
winds along the Northern Rocky Mountain Front. Ended up Bringing
the snowfall into the Southwest slightly faster (1-2 hours faster)
as models are keying in on the wave moving into our area slightly
faster. Brought the gusts up over the Rocky Mountain front,
specifically over Cut Bank who were seeing some of those 35 mph
gusts this morning. -TP

&&

.SYNOPSIS...

A Pacific weather system will continue cloudy skies and gusty winds
across the region today, with the strongest winds along the Rocky
Mountain Front. Snow with this system will spread from the western
Montana mountains today into southwest Montana during the evening
hours. Light accumulating snow is possible in some southwest
valleys. Temperatures will remain above normal over the plains, but
they will be near to slightly below normal in the southwest.

&&

.AVIATION...
Updated 10/1735Z.

VFR conditions are expected to persist across all terminals through
early this evening. Lower clouds and snow begin to push into parts
of Southwest Montana early this evening, mainly impacting KBZN and
KEKS terminals. MVFR to IFR conditions are expected with reduced
visibilities at these sites through the tonight period, then
tapering off overnight. Expect gusty winds to remain over most of
the Northcentral Montana terminals through forecast period, with
winds steadily increasing early Tuesday morning across much of
the area. -TP

&&

.PREV DISCUSSION...
/ISSUED 453 AM MST Mon Dec 10 2018/

Today and Tonight...High pressure over the Treasure State moves
eastward with an area of lower pressure approaching from the west.
With the associated tightening pressure gradient, gusty winds will
be expected across the region, with the strongest winds occurring
along the Northern Rocky Mountain Front where winds are expected to
gust to as high as 48 knots. With this system, snow will spread from
the western Montana mountains into southwestern Montana during the
evening hours, depositing up to an inch and a half of snow
accumulation in its wake.  Temperatures will remain above normal
over the plains, but will be near to slightly below normal in the
southwest. The upper level trof will move quickly eastward and out
of the area, while the next upper level ridge moves in quickly
behind. - Fogleman

Tuesday through Sunday...primary forecast concerns over this period
are 1) accumulating mountain/mountain pass snow Tuesday night
through Wednesday evening; and 2) windy conditions from Tuesday
morning through Wednesday (especially along the Rocky Mountain Front
and Eastern Glacier County) and Thursday through Friday morning
(Rocky Mountain Front and North Central Montana plains.

The first in a series of fast moving open waves will be departing
the Northern Rockies to the east by Tuesday morning, with transitory
ridging quickly building over North Central and Southwest Montana
for the daylight hours of Tuesday. While Tuesday morning will begin
relatively quiet as subsidence associated with the transitory ridge
overspreads the region, a sharpening lee-side surface trough will
lead to a strengthening pressure gradient along the Rocky Mountain
Front. This strengthening pressure gradient combined with increasing
cross barrier flow at H700 of 40 to 60 knots by the late
afternoon/early evening hours on Tuesday, will set the stage for
possible "High Winds" along the Rocky Mountain Front and over
Eastern Glacier County. For this reason, have issued a High Wind
Watch for the aforementioned areas from 19z Tuesday through 17z
Wednesday. The increasing H700 flow will also be responsible for
transporting abundant Pacific moisture eastward into the Northern
Rockies Tuesday night and into the day on Wednesday. Synoptic scale
ascent associated with this second wave will overspread the Northern
Rockies over this same timeframe and work with orographic lift to
produce precipitation, in the form of snow, along the Continental
Divide and over the mountains of Southwest Montana. Given the
already strong winds over the Northern Rocky Mountain Front and
expected snowfall accumulations of 6 to 8 inches at Marias Pass,
have also elected to issue a Winter Storm Watch for the potential of
Blizzard condtions from 00z Wednesday until 18z Wednesday for the
Northern Rocky Mountain Front. Additional Winter Weather Highlights
may be needed for areas/mountain passes of Southwest Montana (i.e.
Beaverhead, Madison, and Gallatin Counties) with future forecasts.
As this second open wave crosses the region Wednesday
afternoon/evening, breezy to windy conditions are expected across
all of Southwest and North Central Montana, but am not expecting
High Wind criteria. As this second wave slides east of the Northern
Rockies, precipitation will quickly come to an end Wednesday
night/early Thursday morning. This will also bring a brief, albeit
only 6-9 hour window, of "lighter" (wind gusts in excess of 30 kts
will likely still be occurring along the Rocky Mountain Front) winds
to the CWA. Cross barrier flow will strengthen along the Rocky
Mountain Front Thursday morning and overspread the plains of North
Central Montana through the day, which will lead to another period
of strong winds into the morning on Friday. This event may require
additional High Wind Highlights, especially along the Rocky Mountain
Front and over the immediate plains west of the Interstate 15
corridor. - Moldan

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  41  24  40  32 /   0   0   0  10
CTB  39  22  38  27 /   0   0   0  20
HLN  36  19  37  25 /  10  10   0  30
BZN  35  17  35  21 /   0  70   0  30
WEY  29   8  23   9 /   0  70  20  70
DLN  32  13  31  17 /   0  40   0  40
HVR  40  19  38  27 /   0   0   0  10
LWT  42  22  38  27 /   0  10   0  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Watch from Tuesday afternoon through Wednesday morning
Eastern Glacier...Northern Rocky Mountain Front...Southern Rocky
Mountain Front.

Winter Storm Watch from Tuesday afternoon through Wednesday
morning Northern Rocky Mountain Front.

&&

$$

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