Wind Chill Advisory 1, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
420 PM MST Sun Dec 31 2017

Aviation Section Updated

.SYNOPSIS...
With high pressure moving southward into the region tonight, expect
very cold temperatures across North Central MT. However, warmer
temperatures have already moved into the higher elevations of
Southwest MT, thus it will not be as cold in that region. Other than
a passing flurry on Monday, it will remain cold over the north and
seasonable over the south. Warmer temperatures will slowly move back
into the entire region throughout next week.

&&

.DISCUSSION...

Tonight through Tuesday...Skies are clearing over an already
bitter cold airmass situated over most of the forecast area. The
coldest temperatures tonight are expected along the HiLine east of
Cut Bank, falling into the -20s and isolated -30s Fahrenheit. A
wind chill advisory has been in place over Toole County today for
apparent temperatures nearing -40F and wind speeds of 10-25 mph.
Confidence is low regarding expansion of areas where forecast
wind speeds are over 10 mph. Conditions will be monitored this
evening for possible extension and expansion of the wind chill
advisory. Anyone outside on this New Year's Eve need to dress
appropriately. Warmer temperatures aloft have yielded temperatures
in the teens to lower 20s above zero for most mountain areas, and
generally along and south of I-90 where the stationary front
persists. Lee troughing develops along the Rocky Mountain Front on
Monday afternoon. This will initiate Chinook winds and begin a
slow and expanding warming trend. With more than two feet of fresh
snow along the Rocky Mountain Front, expect blowing and drifting
snow to create difficult travel conditions Monday into Tuesday.
With rising thickness and Chinook winds, rapid temperature changes
are expected, even rising overnight as the Arctic airmass mixes
out. Temperatures may remain quite cold and below model guidance
in the strongly inverted Helena valley. PN

Tuesday night through Sunday...Overall, a gradual moderation in
temperatures is expected during this period. This trend stems from
the expectation of a high pressure ridge aloft building-in from the
Pac NW. While multiple disturbances are still forecast to ripple
through the ridge, there remains uncertainty regarding when many of
these disturbances will traverse our CWA. Regardless, meager
moisture ahead of these disturbances still looks to limit the
potential of precipitation through Friday. Next weekend, models are
in general agreement that a stronger Pacific disturbance will break-
down the ridge as it crosses our region. Accordingly, POPs increase
somewhat due to a greater influx of Pacific moisture ahead of the
disturbance. At the surface, a predominant lee surface trough is
expected throughout the period. This is especially the case for
North-Central MT. Accordingly, breezy surface winds will become more
prevalent. This may lead to some blowing snow concerns where
temperatures and lingering snowpack permit such conditions.
Jaszka

&&

.AVIATION...
Updated 2320Z.
VFR conditions will prevail for most areas tonight. The exception
will be the Helena/Bozeman areas where some patchy fog could develop
towards 12z Monday. Some mid clouds will move southward through the
region on Monday afternoon, producing a few flurries in the Great
Falls/Helena areas but nothing significant is expected at this time.
Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF -22   4   4  26 /   0   0   0   0
CTB -26   8   2  27 /   0   0   0   0
HLN -12   3   3  25 /   0   0   0   0
BZN  -6  21  -7  25 /   0   0   0   0
WEY  -5  23  -9  27 /   0   0   0   0
DLN   7  28   8  31 /   0   0   0   0
HVR -28 -14 -14  22 /   0   0   0   0
LWT -11  11   5  30 /   0   0   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 11 AM Monday to 11 AM MST Tuesday
Eastern Glacier...Northern Rocky Mountain Front...Southern Rocky
Mountain Front.

Wind Chill Advisory until 8 PM MST this evening Toole.

&&

http://www.weather.gov/greatfalls