Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 280545
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1045 PM MST Sat Dec 27 2014

.UPDATE...
No significant changes to the forecast as the next weather system
begins to impact the area. Have slightly adjusted pops and weather
grids for better agreement with the short term model forecasts and
observations.

&&

.AVIATION...
UPDATED 0545Z.
Confidence in the details of this forecast is low. What can be
said with high confidence is that conditions will deteriorate during
the period. A period of light snow from KGTF to KCTB will spread
east the rest of this evening through after midnight. Brief MVFR
conditions are expected at KGTF and KLWT but could last longer at
KHVR and KCTB. A Canadian cold front will spread south later tonight
through Sunday morning with widespread IFR/LIFR conditions
developing.  This front is expected to reach KCTB around 10z, KGTF
by 14z, KLWT around 15z, then KHLN at 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

&&

.PREV DISCUSSION...
/ISSUED 500 PM MST Sat Dec 27 2014/

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. 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.


&&

.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
Beaverhead.

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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