Winter Storm in Montana, December 3 to 4, 2017

Area Forecast Discussion
National Weather Service Great Falls MT
914 AM MST Sun Dec 3 2017

.UPDATE...
Updated forecast is out. Dropped the winter weather advisory from
just south of the city of Great Falls northward, as the heavier
snowfall will stay south of this region. A mix of light rain/snow
continues to fall around Lewistown and in Southwest MT. Rain
should change to all snow by afternoon. Periods of snow, heavy at
times this afternoon/evening will affect Southwest MT. Kept
advisory in place down there. Made slight adjustments to
temperatures for current trends for today. Brusda

&&

.SYNOPSIS...
An upper level disturbance will move eastward away from the region
tonight. Snow will gradually end from west to east overnight.
Fairly quiet weather conditions are then expected for much of the
upcoming work week, as a ridge of high pressure slowly starts to
build into the region from the west. Afternoon highs will be a few
degrees below normal on Monday and gradually rise to about 5 to 10
degrees above normal by late in the week, especially over the
Plains of north central MT.

&&

.AVIATION...
Updated 1615Z.
Periods of snow will affect Central/Southwest MT into the evening.
The snow could be heavy at times this afternoon/evening. IFR
conditions should be expected, with LIFR possible in/near heavier
snow showers. Precipitation begins to diminish from west to east
after 04z Monday. Mountains will be obscured in many areas through
12z Monday before ceilings begin to rise for most locations.
Brusda

&&

.PREV DISCUSSION...
/ISSUED 448 AM MST Sun Dec 3 2017/

Today through Tuesday...Split trough and its associated cold front
is still expected to bring widespread snow across the CWA today.
This mornings models pushed the main energy even further south.
This might cause a slight shift in the highest snowfall...placing
Great Falls and northward on the bubble...while southern Cascade
County to Helena to Lewistown and southward look to receive the
bulk of the snow. The mountains of sw MT still look to get a foot
or more of snow...while generally 1 to 4 inches is possible
across the lower elevations. Models are also hinting that a mid
level dry layer could bring some brief drizzle or freezing drizzle
this morning across some central areas. Impacts from this look to
be low as recent warm temperatures should help prevent any ice
build up. All things considered decided to keep existing winter
highlights. Some of the more northern ones will need to be
monitored as snowfall could be less impactful with a southerly
shift. While some mountain areas in the central may see
borderline warning level impacts...especially across Kings Hill
Pass. As this wave dives into WY tonight, light to moderate snow
may continue to linger across much of central and southern
portions. Snow should then diminish from north to south Monday
morning. Building high pressure to our west then brings lingering
northwest flow for the remainder of Monday and into Tuesday.
Isolated snow showers will be possible at times in this weakly
unstable pattern. Today's cold front will cool temperatures down
to near normal readings in the 20s and 30s. Northwest flow will
allow for these cooler and more normal temperatures to stick
around. Areas that receive fresh snow could even see morning low
temperatures dip into the teens and single digits. Anglin

Tuesday night through Sunday...Medium range forecast models are
consistent with their solutions for most of this period. Deep upper-
level low pressure troughs over the north central Pacific Ocean and
over eastern North America will keep the forecast area under the
influence of an amplified high pressure ridge. This stagnant pattern
will allow for only slight eastward movement of the ridge axis from
just off the Pacific coast Tuesday night to the Great Basin/Pacific
Northwest by Sunday. Not much moisture is expected to move over the
forecast area in the resulting north-northwest flow aloft, so
passing clouds are expected, but very little chance of
precipitation. Temperatures will very gradually warm from near
normal early in this period to between 5 and 10 degrees above normal
for the weekend. However, temperatures will be slower to warm in the
southwest valleys, as expected new snow cover will pair with high
pressure aloft to develop inversions that will likely be slow to
erode. Have therefore lowered temperatures up to 5 degrees there,
but they may need to be lowered more. The GFS indicates that a
shortwave trough may approach the forecast area from the northwest
on Sunday, which may bring a round of light precipitation, but the
ECMWF does not show this. Will therefore hold off on any mention of
precipitation at this time and monitor the progress of the models.
Coulston

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  33  18  31  21 /  50  20  20  10
CTB  26  13  31  21 /  40  10  10  10
HLN  36  20  28  18 /  90  50  10  10
BZN  35  17  26  10 /  90  50  30  10
WEY  32   9  21   4 /  90  50  10  10
DLN  37  14  25  12 /  90  30  10  10
HVR  34  15  32  20 /  50  10  10  20
LWT  36  16  27  19 /  90  40  20  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 5 AM MST Monday below 5500 feet
for Gallatin...Madison.

Winter Storm Warning until 5 AM MST Monday above 5500 feet for
Gallatin...Madison.

Winter Weather Advisory until 5 AM MST Monday Cascade.

Winter Weather Advisory until 5 AM MST Monday Broadwater...
Central and Southern Lewis and Clark...Jefferson...Meagher.

Winter Weather Advisory until 5 AM MST Monday Fergus...Judith
Basin.

Winter Weather Advisory until 10 PM MST this evening Beaverhead.

&&

http://www.weather.gov/greatfalls

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
806 AM MST SUN DEC 03 2017

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

0800 AM     SNOW             5 S LINCOLN             46.88N 112.68W
12/03/2017  E3.0 INCH        LEWIS AND CLARK    MT   AMATEUR RADIO

            ABOUT 3 TO 4 INCHES OF SNOW OVER NIGHT IN THE DALTON
            MOUNTAIN AREA.

&&

BRUSDA

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
810 AM MST SUN DEC 03 2017

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

0700 AM     SNOW             1 WNW MARYSVILLE        46.75N 112.31W
12/03/2017  E3.0 INCH        LEWIS AND CLARK    MT   TRAINED SPOTTER

            ESTIMATED 3 TO 4 INCHES OF NEW SNOW AROUND GREAT DIVIDE
            SKI AREA.

&&

BRUSDA

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
815 AM MST SUN DEC 3 2017

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

0400 AM     SNOW             17 W WHITE SULPHUR SPRI 46.58N 111.27W
12/03/2017  M3.0 INCH        MEAGHER            MT   MESONET

            MESONET STATION PCKM8, PICKFOOT CREEK
            SNOTEL. THE DURATION OF THE SNOW EVENT WAS
            24 HOURS.

0500 AM     SNOW             10 SSE NEIHART          46.79N 110.68W
12/03/2017  M4.0 INCH        MEAGHER            MT   MESONET

            MESONET STATION DDMM8, DEADMAN CREEK SNOTEL.
            THE DURATION OF THE SNOW EVENT WAS 24 HOURS.

0600 AM     SNOW             18 W WHITE SULPHUR SPRI 46.56N 111.29W
12/03/2017  M5.0 INCH        MEAGHER            MT   MESONET

            MESONET STATION BOMM8, BOULDER MTN SNOTEL.
            THE DURATION OF THE SNOW EVENT WAS 24 HOURS.

0700 AM     SNOW             12 ENE CHECKERBOARD     46.67N 110.33W
12/03/2017  M6.0 INCH        MEAGHER            MT   MESONET

            MESONET STATION DAZM8, DAISY PEAK SNOTEL.
            THE DURATION OF THE SNOW EVENT WAS 24 HOURS.

&&