Heavy Snow in Montana, December 16 to 19, 2021

Area Forecast Discussion
National Weather Service Great Falls MT
420 PM MST Thu Dec 16 2021

...Aviation Section Updated...

.SYNOPSIS...
A strong cold front will move southward through the region
tonight. Expect snow, blowing snow and poor visibility to
accompany the cold front, along with much colder temperatures.
Afternoon highs on Friday are likely to remain below zero in the
Havre area. However, warmer air will start to move back into the
region as early as Saturday, with most areas returning to above
normal temperatures by Sunday afternoon.

&&

.DISCUSSION...
Tonight through Friday night...Overall the current forecast is on
track, with little changes. At 2 PM, the cold front is just north
of Lethbridge, AB and continues to move southward. The cold front
should arrive in Cut Bank around 5 PM, Great Falls around 8 PM
and the Helena area around Midnight. Expect light snow and colder
temperatures to develop behind the front. Overall, 1 to 3 inches
at lower elevations and 3 to 6 inches in the mountains. Most areas
at lower elevations will be closer to an inch, but if some of the
heavier snow showers develop, they could approach 3 inches.
Temperatures will fall about 30 degrees after frontal passage.
Gusty winds for a few hours will also create areas of blowing
snow/poor visibility. Thus the winter weather advisory will
continue for all areas overnight and into Friday morning over
Southwest MT. Wind chills will fall into the -20 to -30 below
range over North Central MT, thus the wind chill highlight will
continue. It was extended though along the Hi-line until 5 AM
Saturday morning. Otherwise, the main concern is the little
warming that will occur on Friday and then how cold does it get on
Friday evening, before things start to warm up. Some adjustments
to the low temperature might occur, as temperatures could fall
quickly on Friday evening before things start to warm up.

Saturday through Thursday...Expect a changeable weather pattern
during this period, as a cold front moves north/then back south
through the region a few times during this period. On Saturday,
all models want to push out the cold air. This might be a bit
fast, thus went below guidance for temperatures northeast of Great
Falls a bit. It is seasonable on Sunday, but the cold front moves
back south on Sunday night, setting up an overrunning situation
for Sunday night/Monday. Another round of about 1 to 3 inches of
snowfall is expected at lower elevations and 3 to 6 inches in the
mountains with this event. Thus winter highlights might be needed
for this event. Temperatures will slowly start to warm back up on
Tuesday, with Wednesday looking to be slightly above normal for
temperatures in some areas. However, the cold air is expected to
move back into the region by next Thursday, it is just a question
on how far south the cold air goes. Thus expect some adjustments
to temperatures next week, depending on exactly where the cold
front is positioned. At this time, precipitation looks fairly
scattered/light for the middle portion of next week, thus impacts
look low at this time for early holiday travel. Brusda

&&

.AVIATION...
420 PM MST Thu Dec 16 2021 (17/00Z TAF period)

VFR conditions persist for most terminals early in this TAF period,
quickly giving way to lowered ceilings and snowfall, reducing
visibility. As a result, expect IFR/LIFR conditions briefly
overnight for most terminals within the region. Mountain obscuration
is forecast, especially along the Rocky Mountain Front as low-level
clouds settle in, but begin to clear out by the end of the period.
- Pierce

Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  -6   1  -3  36 /  90  10   0   0
CTB  -9  -2  -6  34 /  90   0   0   0
HLN   3  15   9  33 /  80  10   0   0
BZN   6  15   4  32 /  80  40   0   0
WYS   7  18   2  19 /  70  40   0   0
DLN  10  21   7  28 /  40  20   0   0
HVR  -9  -3 -11  29 /  80  10   0   0
LWT  -6   2  -2  35 /  70  10   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 3 AM MST Friday Blaine...Eastern
Glacier...Eastern Pondera...Hill...Liberty...Northern Rocky
Mountain Front...Toole.

Wind Chill Advisory from 10 PM this evening to 5 AM MST Saturday
Blaine...Eastern Glacier...Eastern Pondera...Hill...Liberty...
Northern Rocky Mountain Front...Toole.

Winter Weather Advisory from midnight tonight to 10 AM MST
Friday Beaverhead...Broadwater...Gallatin...Jefferson...Madison.

Winter Weather Advisory from 9 PM this evening to 5 AM MST
Friday Cascade...Central and Southern Lewis and Clark...
Chouteau...Eastern Teton...Fergus...Judith Basin...Meagher...
Southern Rocky Mountain Front.

Wind Chill Advisory from midnight tonight to noon MST Friday
Cascade...Chouteau...Eastern Teton...Fergus...Judith Basin...
Meagher...Southern Rocky Mountain Front.

&&

http://www.weather.gov/greatfalls