Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 150333
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
833 PM MST Sun Jan 14 2018

.UPDATE...

Previous forecast is generally on track with just some minor
adjustments this evening. Band of light precipitation pushing
southwestward across north-central MT following the intrusion of a
shallow back door cold front has reached the I-15 corridor and
has also pushed west of far NE zones where skies are clearing.
Precipitation pushing to the S and W continues to be very light
and should gradually decrease in coverage later tonight as moist
layer becomes increasingly shallow due to strong drying moving in
from the NE in mid to upper levels. Due to the very shallow nature
of this moist layer, ice crystals needed for snow growth may be
limited at times, which has resulted in pockets of freezing
drizzle. Clearing skies have moved into NE zones somewhat quicker
than earlier anticipated and temperatures have been falling
quickly across Hill and Blaine counties where minimum
temperatures tonight have been adjusted down some as well.
Hoenisch

&&

.SYNOPSIS...

A cold front will bring widespread light snow from east to west
through tonight. As snow is ending some areas may see areas of
freezing drizzle at times. Snow accumulations of 1 to 3 inches
are expected...with little to no ice accumulation as expected.
Those traveling should use caution. Cold temperatures are also
expected behind this front...with below zero readings possible by
Monday morning for areas across the north and central. Dry and
cold conditions are then expected for Monday as high pressure
moves overhead.

&&

.AVIATION...
Updated 2345Z.

Surface cold front will continue to slide southwest across north-
central and southwest MT this evening. Area of light snow currently
affecting KHVR and KLWT will also shift to the S and W spreading IFR
conditions into KGTF and KCTB early this evening and into the KHLN
and KBZN areas later this evening. Precipitation coverage and
intensity decreases as the band of moisture moves to the SW, but low
clouds and some potential for freezing drizzle will exist through a
portion of tonight. Drier air works SW across the region late
tonight though Monday morning fore clearing skies. Hoenisch

&&

.PREV DISCUSSION...
/ISSUED 445 PM MST Sun Jan 14 2018/

Tonight through Tuesday...Backdoor cold front is currently pushing
across northern and eastern portions of the CWA this afternoon.
This has been progressing as forecasted as light snow continues
to fall all along this boundary...with visibilities down to around
a mile. Expect light snow to impact much of the northern and
central portions of the CWA this afternoon and evening...with the
remaining part of the CWA seeing chances for brief light snow
tonight. As this front progresses westward tonight it starts to
loose its upper level support...and more importantly its
moisture. This will generally keep new snow accumulations
light...around an inch or two. However, this may introduce
chances for freezing drizzle as the saturation layer in model
soundings appears to be shallow and warmer than the ideal snow
zone. As a result have added in the mention for freezing drizzle
tonight into Monday morning where low level moisture lingers. This
will mainly be along the high plains along the Rocky Mountain
Front, to Great Falls, to Helena, and southward...with the best
chances coming from the Helena Valley through southwest Montana.
Any ice accumulations will be light...but may be enough to cause
travel impacts. Confidence is only moderate for a widespread
event so have held off on any advisories for now.
Meanwhile...areas behind the front will see clearing skies and
very cold temperatures return tonight. A light breeze will bring
dangerous wind chills to the Hi-Line. Winds look to be just shy
of Wind Chill Advisory Criteria...however...dangerous wind chills
of up to -25 are possible across the Hi-Line tonight. Monday will
see a large ridge build back in the region...ending any lingering
precip or drizzle in the morning...and bringing cool temperatures
behind todays front. Northern and central areas will struggle to
get into the single or double digits...while southwest MT sees 20s
and 30s. This ridge sticks around through Monday night...keeping
dry and cool conditions. Ridge then breaks down Tuesday with most
areas expected to warm back to near normal temperatures...except
across far north central portions. Tuesday will also see some
increased clouds...however...mainly dry conditions should
continue. Anglin

Tuesday Night through Sunday...A shortwave system crosses the
PacNW and moves into Montana Tuesday night behind the collapsing
ridge. Temperatures will moderate quickly, trending near to above
seasonal averages with gusty downslope winds. Precipitation
associated with this wave will be scattered in nature, producing
light snow mainly over some mountain areas. Seasonally mild
conditions continue Thursday and Friday under a progressive
westerly flow aloft. This pattern will produce areas of snow
generally over the mountains and more broadly across southwest MT.
Temperatures trend cooler into the weekend, with chances for snow
continuing as Pacific moisture crosses the region amid a broad
split flow pattern. PN

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF   7  18   5  34 /  80  10   0   0
CTB   1  15   1  31 /  60  10   0   0
HLN  18  24   6  27 /  20  20   0   0
BZN  16  28  -2  29 /  30  20   0   0
WEY  15  29  -5  30 /  10  20   0   0
DLN  23  31  12  36 /  20  20   0   0
HVR -13   3 -11  15 /  40  10   0   0
LWT   0  18   3  35 /  80  10   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

http://www.weather.gov/greatfalls



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