Winter Storm in Montana, January 10, 2020

Area Forecast Discussion
National Weather Service Great Falls MT
850 PM MST Fri Jan 10 2020

.SYNOPSIS...
A moist westerly flow aloft tonight will allow for snow to fall over
the Rocky Mountain Front and portions of Southwest MT. Seasonable
temperatures on Saturday will give way to an arctic cold front
moving south through the region on Sunday. Another round of
widespread snow is expected Sunday into Monday, along with very cold
temperatures moving into the region. Expect the very cold
temperatures to last through much of next week.

&&

.UPDATE...
Updated forecast is out. Main adjustment was to updated temps/pops
to current trends. Overnight lows should not fall too much tonight
with winds/cloud cover. Pops increased a bit in Southwest MT as
the next upper level disturbance moves through that region
tonight. Expanded the winter weather advisory to all elevations of
Beaverhead, Madison and Gallatin counties. Otherwise, all else
seems on track. Brusda

&&

.AVIATION...
Updated 515 PM MST Fri Jan 10 2020 (00Z TAF Period)

Main concern overnight is an area of light snow over the divide and
across Southwest MT, along with windy conditions/low level wind
shear over the Northern Plains tonight. Expect IFR/MVFR conditions
in/near areas of snow. Bozeman could be impacted for a few hours
between 06z and 12z Saturday. Wind shear could be an impact this
evening over North Central MT. Expect lighter snowfall on Saturday,
with the main arctic cold front to move into North Central MT on
Saturday night. Mountains/passes likely obscured for much of
the period. Brusda

&&

.PREV DISCUSSION...
/ISSUED 515 PM MST Fri Jan 10 2020/
Tonight through Sunday...Breezy conditions and warming temperatures
have been the main story so far today. Some breezy winds have
brought areas of blowing and/or drifting snow. An upper level
disturbance will push through tonight continuing breezy winds and
the threat for blowing/drifting snow. Snow showers will generally be
confined to the mountains and portions of Southwest Montana. As a
result have expanded the Winter Weather Advisory to including the
entire Rocky Mountain Front and some higher elevation areas of the
southwest including Monida pass and the West Yellowstone areas.
Areas in the advisories could see 2 to 6 inches, with higher amounts
across the mountains, and periods of blowing snow. Meanwhile this
disturbance may bring some isolated to scattered snow showers across
the north and central with mild temperatures tonight. Westerly flow
will then be found for Saturday, with lingering mountain snow and
near normal temperatures for most areas. Winds will relax a bit for
Saturday although may be just enough to bring blowing/drifting snow
for areas with fresh snowfall. Saturday night through Sunday then
sees the next push of arctic air across the region. Still some
details to work out although confidence is high temperatures will
begin to cool and areas of snow will be found. So far the snow
confidence is high enough to place a Winter Storm Watch along the
Rocky Mountain Front from Sunday through Monday. Here snowfall could
be over a foot and gusty winds may bring periods of blowing and
drifting snow. Elsewhere, snow looks for fall along the front
although timing and locations are still being worked out. Be sure to
check for the latest details. Temperatures will also start to cool
along and behind the front on Sunday, mainly across central and
northern portions while southwest MT remains near to only slightly
below normal. Anglin

Sunday night through next Saturday...Some of the coldest air of the
season is expected during this period, especially for the first
half of the week. Widespread sub- zero temperatures are expected
by Sunday night for Central and North-Central locations, with most
of these areas struggling to reach zero during the day on Monday.
Overnight lows will fall to as low as 40 below and colder along
the Hi-Line Tuesday and Wednesday mornings. The cold air will
likely reach the southwest by late Monday into Tuesday, although
current guidance is struggling with how fast it will move into
this area. Wind chill products will considered in the coming days
as hypothermia and frostbite will increasingly become a real
threat due to the dangerously cold temperatures. The unsettled
nature of this pattern will also bring periods of snow. Best
chances right now look to come Monday and Tuesday, although timing
and exact locations are still being determined. Overall most
locations will have a chance for snow, with cold temperatures, and
perhaps extreme wind chills at times in the long term period.
Anglin

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  28  36  10  16 /  10  10  20  20
CTB  23  28  -3   2 /  10  20  30  30
HLN  19  34  22  30 /  50  20  20  20
BZN  25  34  20  32 /  60  20  30  20
WYS  10  21   8  17 / 100  60  60  70
DLN  19  27  16  27 /  70  20  20  10
HVR  18  31   4   6 /  40  10  40  30
LWT  25  35  13  20 /  30  10  20  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 5 AM MST Sunday Central and
Southern Lewis and Clark...Southern Rocky Mountain Front.

Winter Storm Watch from Sunday morning through Monday afternoon
Northern Rocky Mountain Front...Southern Rocky Mountain Front.

Winter Weather Advisory until 3 PM MST Saturday Beaverhead...
Gallatin...Madison.

Winter Weather Advisory until 5 AM MST Sunday Northern Rocky
Mountain Front.

&&

http://www.weather.gov/greatfalls

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
514 PM MST FRI JAN 10 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0409 PM     NON-TSTM WND GST 4 NNE MCALLISTER        45.50N 111.70W
01/10/2020  M55 MPH          MADISON            MT   MESONET

            MESONET STATION MTNOR NORRIS HILL (MT DOT).

&&

BRUSDA

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
703 PM MST FRI JAN 10 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0615 PM     NON-TSTM WND GST 1 SW THREE FORKS        45.88N 111.57W
01/10/2020  M56 MPH          GALLATIN           MT   AWOS

            AWOS STATION K9S5 1 SW THREE FORKS.

&&

MOLDAN