Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 280000
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
500 PM MST Sat Dec 27 2014

UPDATED AVIATION DISCUSSION

...WIDESPREAD SNOW...BLOWING SNOW AND CONTINUED TRAVEL IMPACTS
TONIGHT THROUGH MONDAY...

...MUCH COLDER TEMPERATURES EARLY NEXT WEEK...

.DISCUSSION...

Tonight through Monday...Light snow is beginning to develop over the
higher terrain along the Rocky Mountain Front and Little Belts this
afternoon ahead of the main trough of low pressure. As this low
deepens over the Northern Rockies, snow will begin developing
over north-central Montana between 9pm and midnight, then become
widespread into southwest Montana by early Sunday morning. Overall,
the period of heaviest snowfall is expected between midnight and 6
pm Sunday. Snow will continue into Sunday night but is expected to
diminish from north to south by Monday morning.

In addition to snow, gusty north winds of 10 to 20 mph with gusts to
30 mph are anticipated on Sunday, which will create blowing and
drifting snow. Near whiteout conditions are also possible along the
Rocky Mountain Front including Marias Pass, East Glacier and
Browning. Snow amounts in higher elevations at and above pass level
along the Continental Divide and central mountain ranges will range
from 8 to 12 inches with 3 to 6 inches in lower elevations below
pass level. Given this combination of snow and blowing snow, travel
could be very hazardous. A Winter Storm Warning is in effect now
through Monday morning for all elevations along the Rocky Mountain
Front as well as the Little Belts above 6000 feet, which includes
Kings Hill Pass. Have also issued a Winter Storm Warning beginning
late tonight for Chief Joseph Pass area in northwest Beaverhead
County. In the valleys across southwest Montana as well as areas
along the Hi-Line, snow accumulations of 2 to 5 inches of snow is
expected with 5 to 10 inches in the mountains above pass level.
Winter Weather Advisories are in effect for these areas beginning
late tonight. A cold airmass will follow the snow with temperatures
steadily falling into the teens and single digits during the day on
Sunday with highs around 0 on Monday. MLV

Monday night through Saturday...Medium range period begins with
scattered light snow ending over the area as the upper trof
responsible for the snow continues to push south and away from the
area. A strong upper ridge builds over the eastern Pacific on
Tuesday and Wednesday resulting in a northerly flow over the area
that will be dry and cool. The only precipitation will occur over
the Northern Rocky Mountain Front. By Thursday, shortwave energy
will begin to rotate south out of western Canada and will spread
light snow across the Hi-Line. Moisture and upslope lift associated
with the shortwave will result in widespread light snow developing
Friday across the area which will continue through Saturday. The
coldest temperatures will occur Tuesday morning with readings
generally in the teens below zero and highs reaching only the single
digits above zero during the afternoon. Temperatures will slowly
moderate during the week though readings will remain below seasonal
averages. By the end of the week, another round of cooler air will
push across the border from Canada.

&&

.AVIATION...
UPDATED 0000Z.
Confidence in the details of this forecast is low. What can be
said with high confidence is that conditions will deteriorate during
the period. Snow is expected to spread east this evening through
after midnight. What is uncertain is whether this snow will be
confined to the mountains with VFR conditions continuing for the
lower elevations or whether MVFR or even IFR conditions will set in
for the lower elevations. Feel the best chance for IFR/LIFR
conditions to develop is with and behind a Canadian cold front as it
spreads south later tonight through Sunday morning. This front is
expected to reach KCTB around 10z, KGTF by 14z, KLWT around 15z,
then KHLN 16z or 17z, and KBZN shortly around 19z. Mountain
obscurement over the Rocky Mountain Front will spread to the
remainder of the forecast area no later than late tonight or early
Sunday morning. Blank

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  16  22  -7   0 / 100 100  60  20
CTB  11  16 -13  -5 / 100 100  30  10
HLN  17  21   0   5 / 100 100  40  20
BZN  11  21  -4   7 / 100 100  60  20
WEY   9  22  -7   5 / 100 100  70  20
DLN  12  24   1   9 / 100 100  40  20
HVR  16  18  -4   3 / 100  90  30  10
LWT  16  21  -4   3 / 100 100  60  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY until 6 AM MST Monday Cascade...Central
and Southern Lewis and Clark...Chouteau...Eastern Glacier...
Eastern Pondera...Eastern Teton...Fergus...Judith Basin...
Meagher...Toole.

WINTER WEATHER ADVISORY from Midnight tonight to 6 AM MST Monday
Beaverhead...Blaine...Broadwater...Gallatin...Hill...Jefferson...
Liberty...Madison.

WINTER STORM WARNING from Midnight tonight to 6 AM MST Monday
for Chief Joseph Pass area.

WINTER STORM WARNING until 6 AM MST Monday FOR ELEVATIONS ABOVE
6000 FEET FOR Cascade...Judith Basin...Meagher.

WINTER STORM WARNING until 6 AM MST Monday Northern Rocky
Mountain Front...Southern Rocky Mountain Front.

&&

$$

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