High Wind in Montana, February 17, 2018

Area Forecast Discussion
National Weather Service Great Falls MT
500 PM MST Sat Feb 17 2018

...UPDATED AVIATION SECTION...

.SYNOPSIS...

A strong storm system tracking east across the region tonight
will continue to spread snow across much of the area with
steadiest snow and greatest snow accumulation expected across
western portions of north central Montana. Periods of snow will
increase over southwest Montana as well tonight with a brief but
intense snowband accompanied by gusty winds expected this evening.
Gusty north winds will develop tonight as the low pressure center
moves off to the east and much colder air pours south into the
region from Canada.

&&

.DISCUSSION...

Tonight through Monday...Strong shortwave and surface low now
moving onshore in far SW BC will continue ESE tonight with main
focus for widespread and at times moderate to heavy snow
continuing to be focused across N-central MT and particularly NW portions
of the forecast area from I15 west to the Rocky Mtn Front where
synoptic and frontogenic lift will combine with low level upslope
flow. Further east, snow amounts have been reduced slightly from
previous forecasts but still support 5-8inches across much of
north-central MT east of I15 through Sunday night with bulk of the
snowfall coming tonight followed by periods of lighter snow. From
Helena south through SW MT the airmass south of the surface to
mid level low will be slightly unstable with strong winds aloft
tonight. Snow showers will likely organize into bands later this
afternoon and evening with hi-res models supporting a more
intense E-W band of snow likely to develop around the I90 corridor
later this evening then sink south with the passage of the mid
level shortwave. With potential for convective elements in the
snow band, some stronger wind gusts to 50mph or more are not out
of the question, resulting in a brief but intense snow squall,
potentially moving through the Bozeman area between 9pm and
Midnight. Otherwise, total snow accumulation across SW MT remains
the same and generally less than 5 inches except over the higher
mountain ranges. Winds also increase across north-central MT
overnight as as the surface low moves east and a much colder
airmass surges south from AB. By sunday morning, temperatures
across north- central MT should be in the single digits and remain
steady with wind chill values in the teens and twenties below
zero and north winds around 10-15 mph. Upper trough continues to
deepen over the western US Sunday and Monday as additional
shortwave energy drops south along the coast. Cold cyclonic flow
aloft over the region with high pressure at the surface will
maintain cold temperatures through Monday though cloudy conditions
persist with periods of light snow. Hoenisch

Monday Night through Saturday...Forecast models are in generally
good agreement with the overall pattern solution of a deep,
positively-tilted low pressure over the western and central United
States through the period. The resulting north-northwest flow aloft
will keep the forecast area very cold through at least Tuesday night
with very little chance for snow. Lows Monday night will fall well
into the teens and 20s below zero with 5 to 10 mph winds potentially
causing wind chills in the -30s and -40s below zero. A series of
disturbances will then likely bring an increasing chance of snow to
the mountains for Wednesday through Saturday, but increasing
westerly downslope winds over the plains will hinder significant
precipitation development there. These winds will also help warm
temperatures gradually through this part of the period, but the
likely widespread snow coverage from recent storms will likely
prevent significant warming and keep temperatures 5 to 10 degrees
below normal (forecast highs mostly in the 20s and forecast lows
mostly in the 5 to 15 above zero range).
Coulston

&&

.AVIATION...
Updated 0000Z.

A cold front just south of a KGTF-KLWT line will move south to a
KBZN-KDLN line through 12Z then south of this line after 12Z. As a
result, widespread light to moderate snow will continue MVFR/IFR
conditions across north central and central Montana through 12Z.
Breezy and gusty east winds will also shift more northerly by 06Z,
causing widespread blowing and drifting of snow. Snow will then
decrease from the northwest after 12Z, for more VFR/MVFR conditions,
but IFR conditions will still be possible in the KHLN and KLWT
areas. Snow will be more showery in nature across southwest Montana,
which will cause VFR/MVFR conditions to quickly worsen to IFR in
those showers. Strong mid level westerly winds will also cause
mountain wave turbulence and low level wind shear, and they will
likely mix down to the surface there at times with the showers,
causing gusts of up to 35 kt mainly through 12Z.
Coulston

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF   0   2 -15  -7 / 100  70  60  40
CTB  -2  -2 -20  -4 / 100  70  40  30
HLN   9  11 -11   1 /  80  60  60  30
BZN  16  18 -10   1 / 100  80  60  30
WEY  18  24 -13   9 / 100  90  80  40
DLN  23  24  -9   1 /  70  60  70  30
HVR   0   4 -18  -5 / 100  70  30  30
LWT   1   3 -13  -4 / 100  70  50  40

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 5 AM MST Monday Beaverhead...
Broadwater...Central and Southern Lewis and Clark...Gallatin...
Jefferson...Madison.

Winter Storm Warning until 5 AM MST Monday Central and Southern
Lewis and Clark...Eastern Glacier...Eastern Pondera...Eastern
Teton...Northern Rocky Mountain Front...Southern Rocky Mountain
Front...Toole.

Winter Storm Warning until 5 AM MST Monday Blaine...Cascade...
Chouteau...Fergus...Hill...Judith Basin...Liberty...Meagher.

Ice Jam Flood Warning continues until 915 PM MST Monday for the
Missouri River near Townsend in central Broadwater County.

&&

http://www.weather.gov/greatfalls

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1245 PM MST SAT FEB 17 2018

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

1245 PM     SNOW             9 WSW FORESTGROVE       46.95N 109.26W
02/17/2018  M8.0 INCH        FERGUS             MT   TRAINED SPOTTER

&&

JAA