Area Forecast Discussion
Issued by NWS Great Falls, MT

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684
FXUS65 KTFX 142158
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
258 PM MST Thu Dec 14 2017

.SYNOPSIS...

Stubborn freezing fog is expected to persist in the valleys of
Southwest Montana through Friday morning. Accumulating snow will
then overspread the region from northwest to southeast late Friday
morning through early Saturday morning. Precipitation will fall
as rain or a rain/snow mix at lower elevations on Friday before
changing to snow that evening. The snow will then end gradually
later Saturday morning through early Sunday morning.

&&

.DISCUSSION...

Rest of today through Saturday night...High pressure ridging aloft
will break-down on Friday as a disturbance continues approaching
from the Gulf of Alaska Region. This disturbance will then cross
our area on Saturday and be followed by high pressure aloft
building-in from the west by early Sunday morning. At the surface,
a Canadian cold front will cross the border and enter the Hi-Line
Friday afternoon. This front is then expected to stall along the
Rocky Mountain Front and Central Montana mountains by Friday
evening. It will then remain there through Saturday before
dissipating thereafter. Above-normal temperatures will prevail
over North-Central Montana ahead of the cold front, then cool
somewhat behind the front for Friday night through Saturday night.
With recent cold air entrapment in the valleys of Southwest
Montana, overall cooler readings are expected there throughout the
period.

Predominantly fair weather is expected to continue through Friday
morning. However, patchy freezing fog should persist in the
Southwest Montana valleys before dissipating toward noontime on
Friday. In addition, gusty downslope winds are expected to develop
over North-Central Montana overnight tonight into Friday, but
model guidance indicates peak gusts should remain below high wind
criteria. The aforementioned disturbance will allow snow to
overspread our region from northwest to southeast late Friday
morning through early Saturday morning. Thereafter, the snow will
taper-off gradually and end area-wide by early Sunday morning. At
lower elevations, precipitation will fall as rain or a rain/snow
mix for a time on Friday before changing to snow that evening.
Snow totals are still expected to reach a trace to 3 inches for
the plains/valleys, with totals of up to a foot in the mountains.
Issued winter weather advisories for Marias Pass and Kings Hill
Pass, where confidence is high accumulating snow will impact
travel. Will let future shifts decide if advisories need to be
expanded in areal coverage.
Jaszka

Sunday through Thursday...An unsettled weather pattern will reside
over the region, with a gradual shift towards colder temperatures
over North Central MT by late in the period. Breezy west winds
develop on Sunday allowing the I-15 corridor to warm up a bit from
Great Falls to Cut Bank, otherwise expect another round of light
snow to move through the region late Sunday night through Monday. A
few snow showers linger into Tuesday, otherwise the next major
weather system will be the cold front pushing southward from Canada
into Montana Wednesday into Thursday. A much colder air mass will
follow on the heels of this system under northerly upper level flow
late Wednesday through the end of next week.
CC/Brusda

&&

.AVIATION...
Updated 1733Z.

Mainly VFR are forecast for the next 24-hours. Expect northerly to
northwesterly flow aloft and passing upper-level clouds. Patchy
freezing fog and associated CIGS/VSBY down to LIFR should dissipate
by 20Z/Thur in SW MT valleys. Westerly surface winds strengthen
along and near the Rocky Mountain Front, including KCTB, by late
this evening. Mountain wave activity will also increase as a Pacific
disturbance begins its approach.
Jaszka

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  34  45  27  33 /   0  10  70  50
CTB  33  42  24  33 /   0  40  70  40
HLN  22  37  24  30 /   0   0  60  40
BZN  16  36  21  29 /   0   0  70  50
WEY  10  25  16  24 /   0   0  80  50
DLN  20  37  22  30 /   0   0  40  30
HVR  30  42  25  36 /   0  40  60  20
LWT  31  47  25  30 /   0   0  70  40

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Freezing Fog Advisory until 5 PM MST this afternoon Beaverhead...
Broadwater...Central and Southern Lewis and Clark...Gallatin.

Winter Weather Advisory from 5 PM Friday to 11 PM MST Saturday
Cascade...Judith Basin...Meagher.

Winter Weather Advisory from 11 AM Friday to 11 AM MST Saturday
Northern Rocky Mountain Front.

&&

$$

http://www.weather.gov/greatfalls



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