Special Weather Statement, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
1020 PM MST Sun Jan 17 2021

.UPDATE...

Only minor insignificant changes were made to the grids and
forecast, with no impacts to sensible weather. Raised RHs across
the plains to match current observations.

&&

.SYNOPSIS...
A passing weather disturbance will keep mostly mountain snow
going through Monday evening. The snowfall will be heaviest in the
Kings Hill and Big Sky regions. Drier but breezy to windy
conditions move into the region for the middle portion of the
week. Colder temperatures along with a potential for snow can be
expected for next weekend.

&&

.AVIATION...
1020 PM MST Sun Jan 17 2021 (18/00Z TAF period)

Periods of MVFR/near-MVFR conditions are expected at all terminals
outside of KCTB for most of the 1806/1906 TAF period as an upper
level disturbance crosses the Northern Rockies. The most persistent
MVFR and even IFR conditions are expected at the KEKS, KBZN, KLWT,
and KHVR terminals due to northerly upslope flow, which will help to
produce snow over/near these terminals and over the adjacent
mountain ranges. Mountains will be obscured for most if not all the
TAF period. - Moldan

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

&&

.HYDROLOGY...
300 PM MST Sun Jan 17 2021

The flood advisory continues for the Jefferson River near Three
Forks until further notice.

The river gauge reading there continues to hover around minor
flood stage, with little variation over the last 24 hours.

Although no reports of flooding have been received so far, the
current forecast indicates that the river level should remain near
flood stage for the time being. Any impacts from this ice jam
should be minor and along the river bank.

&&

.PREV DISCUSSION...
/ISSUED 454 PM MST Sun Jan 17 2021/

Remainder of this afternoon thru Monday night...A Pacific cold
front, supported by an approaching shortwave trough, is currently
moving west to east through North-central and Southwest Montana. A
Gusty west to northwesterly wind shift, along with scattered
rain/snow showers are being observed along and behind this front.
Otherwise light snow and some blowing snow has been mostly
confined to mountain areas. The elevated cold front associated
with the shortwave trough moves in this afternoon and tonight,
bringing a further increase in mountain snow, especially over the
Little Belts and the Big Sky regions. Snow accumulations of 6 to
12 inches of snow can be expected over King's Hill area through
Monday evening, with slightly less amounts expected in the Big Sky
area. Other mountain areas will generally fall in the 1 to 3 inch
range for snow accumulations. Most lower elevation areas will see
little to no snow accumulation, with the exception of the
northwest facing slopes in between Great Falls and Lewistown,
where 2 to 6 inches of accumulation will be possible. The eastern
portions of the Bozeman area may see a few inches as well. The
only change to the current winter highlights was to extend the
Rocky Mountain Front advisory to 8 am Monday per coordination with
the Missoula forecast office. Cooling in the wake of this system
will be modest, with lows tonight remaining above what is normally
expected this time of year for most locations. Unstable northerly
flow aloft will keep snow snow going for much of the day on
Monday for the Central and southwest mountains, though the
activity may be more showery in coverage.

Tuesday through Thursday...There is the potential for a short
period of strong winds Tuesday afternoon into early Wednesday
morning over the Northern Rockies and in the Cut Bank area. A high
wind watch was issued for these locations in anticipation of the
strong winds. Other areas over the plains will be windy as well
but not quite to high wind criteria. Otherwise, expect slightly
above normal temperatures for Tue/Wed...with colder air starting
to move into the region on Thursday. Snowfall chances have
decreased during this period compared to what the forecast had a
few days ago, thus now only a passing snow shower is possible. RCG

Friday thru Sunday...Generally below normal temperatures are
expected by next weekend, as an upper level trough swings through
the region. Some very cold air in southern Canada will try to
move southwestward into the Havre area...the question is how far
though? Thus expect adjustment to temperatures in this region over
the next few days. Also the GFS is more aggressive with snowfall
next weekend along the cold air boundary than the EC model is.
There still is quite a bit of uncertainty in the forecast for next
weekend in terms of where/when/how much snowfall might fall, went
with NBM pops for now. RCG/Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  29  40  21  42 /  20  30   0   0
CTB  29  38  21  41 /  30  30   0   0
HLN  31  38  18  38 /  20  30   0   0
BZN  22  34  13  35 /  40  40  10   0
WYS   6  23  -5  25 /  50  30  10   0
DLN  20  34  11  33 /  10  20   0   0
HVR  28  39  21  42 /  30  20   0   0
LWT  26  32  16  38 /  80  70   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 9 PM MST Monday above 4000 feet
for Cascade...Fergus...Judith Basin...Meagher.

Winter Weather Advisory until 8 AM MST Monday Northern Rocky
Mountain Front...Southern Rocky Mountain Front.

High Wind Watch from Tuesday morning through Wednesday morning
Eastern Glacier...Northern Rocky Mountain Front...Southern Rocky
Mountain Front.

Winter Weather Advisory until noon MST Monday Gallatin.

Winter Weather Advisory until noon MST Monday above 5000 feet
for Central and Southern Lewis and Clark...Jefferson.

&&

http://www.weather.gov/greatfalls

Special Weather Statement
National Weather Service Great Falls MT
948 PM MST Sun Jan 17 2021

MTZ012-013-050-051-054-180645-
Chouteau-Cascade-Fergus-Judith Basin-Meagher-
948 PM MST Sun Jan 17 2021

...AN AREA OF HEAVY SNOW WILL AFFECT NORTH CENTRAL MONTANA
THROUGH MIDNIGHT...

At 945 PM MST, an area of heavy snow was located from near
Belt, eastward to Stanford, moving southeast at 15 mph.

Winds in excess of 30 mph are possible with this area of heavy snow.

This includes the following portions of Highway 200 from east of
Great Falls to Lewistown...and Highway 89 from Belt to White Sulphur
Springs.

Snowfall rates near 1 inch per hour along with visibility below one
half mile is expected in this region through Midnight.

Conditions can deteriorate rapidly in winter weather situations. Be
prepared for snow or ice covered roads. Slow down and allow extra
time when traveling.

LAT...LON 4734 11128 4742 11047 4686 10966 4675 11103
TIME...MOT...LOC 0445Z 315DEG 11KT 4724 11059

Brusda

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1055 PM MST SUN JAN 17 2021

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

0226 PM     NON-TSTM WND GST 13 S MARYSVILLE         46.56N 112.31W
01/17/2021  M65 MPH          LEWIS AND CLARK    MT   MESONET

            MESONET STATION MTMDP MACDONALD PASS (MT
            DOT).

&&

BRUSDA

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1056 PM MST SUN JAN 17 2021

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

0200 PM     NON-TSTM WND GST 16 SE GALLATIN GATEWAY  45.44N 110.95W
01/17/2021  M52 MPH          GALLATIN           MT   MESONET

            MESONET STATION GNFHY 10.7 W EMIGRANT
            (AVALANCHE).

0224 PM     NON-TSTM WND GST 1 N LOMA                47.95N 110.50W
01/17/2021  M57 MPH          CHOUTEAU           MT   MESONET

            MESONET STATION MTLOM LOMA (MT DOT).

0258 PM     NON-TSTM WND GST 2 NW WINDHAM            47.10N 110.17W
01/17/2021  M52 MPH          JUDITH BASIN       MT   AWOS

            AWOS STATION K1CM CHARLIE.

0452 PM     NON-TSTM WND GST 7 ESE HILGER            47.22N 109.22W
01/17/2021  M57 MPH          FERGUS             MT   MESONET

            MESONET STATION JPKM8 JUDITH PEAK RAWS.

0458 PM     NON-TSTM WND GST 1 E ROY                 47.33N 108.93W
01/17/2021  M56 MPH          FERGUS             MT   AWOS

            AWOS STATION K1OM OSCAR.

0600 PM     NON-TSTM WND GST 6 WSW BIG SKY           45.24N 111.44W
01/17/2021  M67 MPH          MADISON            MT   MESONET

            MESONET STATION YCAMS 5.7 W BIG SKY
            (AVALANCHE).

0603 PM     NON-TSTM WND GST 3 WNW TOWNSEND          46.33N 111.59W
01/17/2021  M56 MPH          BROADWATER         MT   MESONET

            MESONET STATION GINM8 GINGER RAWS.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GREAT FALLS MT
1058 PM MST SUN JAN 17 2021

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

1145 AM     NON-TSTM WND GST 5 N LEDGER              48.34N 111.82W
01/17/2021  M58 MPH          PONDERA            MT   MESONET

            MESONET STATION MTM73 LEDGER N MDA.

&&

BRUSDA

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