Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 202336
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
435 PM MST Sat Dec 20 2014

Updated Aviation Discussion

.DISCUSSION...

Tonight through Monday...A plume of moisture is pushing through
the Pacific Northwest on a strong westerly jetstream. Ridging
further west will turn the upper level flow northwesterly,
positioning western and southwest Montana beneath the jet exit
region. A shortwave trough will move through this flow from
British Columbia to eastern Montana, causing a lee surface trough
to develop. The overall result is heavy mountain snow, areas of
light rain at low elevations, and strong winds across central
Montana. Little, if any precipitation is expected for western
portion of the central plains. Areas of light freezing rain are
possible tonight generally north and east of the Bears Paw
mountains as warmer air spreads over a colder airmass in northeast
Montana.

Wind gusts will strengthen along the Rocky Mountain Front early
Sunday where a high wind warning remains in effect. Strong wind
gusts will extend further east onto the adjacent plains, but the
high wind watch continues with lowered confidence that winds here
will reach warning criteria. Winter weather advisories now cover
the Rocky Mountains above 5000 feet and for the Central and
Southwest mountains above 5500 feet. Travelers through mountain
passes on Sunday should expect snow covered and icy roads. Snow
will be later to start in the Little Belt and other central
Montana ranges...and will likely continue later into Monday. Nutter

Monday night through Saturday...Shortwave ridge develops over the
region Monday night into Tuesday afternoon with dry conditions at
lower levels but scattered to numerous showers over the mountains.
Temperatures are expected to be generally near or above seasonal
averages. For Christmas Eve and Christmas Day...a Pacific storm
system will affect much of the region. At this time, it appears
that anticipated snow amounts west of a line from Cut Bank to
Lewistown should see 3 to 5 inches of snow over the plains with 6
to 15 inches in the mountains. For areas east of this line...snow
accumulations should range from 1 to 4 inches over the plains with
3 to 8 inches in the mountains. It should be noted that the record
snowfall for Great Falls on Christmas day is only 4.4 inches...and
we might have a chance at that record should a heavier snowband
move through Great Falls. Overall this is not a major storm...but
the timing for precipitation during a major holiday period will
affect travel. Temperatures will also trend colder from Wednesday
through Friday. There is the chance that temperatures on Christmas
Day could be a bit colder than currently forecast because of
clouds/snowfall. After this storm exits the region late
Thursday/early Friday...the weather pattern will become a bit less
active. There will be a small chance for a passing snow shower
over the weekend and into the New Years week...but no significant
snowfall is expected at this time. The main concern tonight is the
GFS13/EC are hinting at some very cold air moving into the region
by Tue Dec 30th...again this is a ways out...and things can change
a bit...but at this time current models are trying to bring down
another batch of arctic air before New Years. Brusda/mpj


&&

.AVIATION...
UPDATED 2335Z.
A strengthening and increasingly moist West/Northwest flow aloft
will move across the Northern Rockies and MT tonight through Sunday.
This will spread increasing cloudiness across the region tonight
with precipitation and terrain obscurations increasing over the
mountains tonight and continuing through Sunday. Precipitation will
spread into the KBZN terminal vicinity after 06z with occasional
MVFR in lower CIGS/-SN late tonight through Sunday morning before
conditions improve some Sunday afternoon. Precipitation will be less
widespread at lower elevations of Central/N-Central MT. W-NW winds
aloft increase to around 50kts at ridgetops Sunday with Mtn wave
turbulence likely east of the Rockies and gusty surface winds likely
at most terminals. Hoenisch

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  36  49  31  39 /  20  50  30  30
CTB  30  43  28  36 /  20  40  30  20
HLN  30  47  31  38 /  50  80  40  30
BZN  31  45  27  34 /  70  90  50  30
WEY  30  39  21  31 / 100 100  90  50
DLN  34  46  29  35 /  70  90  60  30
HVR  25  44  27  38 /  20  70  20  20
LWT  31  48  30  37 /  30  80  40  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY from 7 PM this evening to 5 AM MST
Monday FOR ELEVATIONS ABOVE 5000 FEET FOR Central and Southern
Lewis and Clark...Jefferson...Northern Rocky Mountain Front...
Southern Rocky Mountain Front.

HIGH WIND WATCH from late tonight through Sunday afternoon
Eastern Glacier...Eastern Pondera...Eastern Teton...Liberty...
Toole.

HIGH WIND WARNING until 5 PM MST Sunday Northern Rocky Mountain
Front...Southern Rocky Mountain Front.

WINTER WEATHER ADVISORY from 7 PM this evening to 5 AM MST
Monday FOR ELEVATIONS ABOVE 5500 FEET FOR Beaverhead...
Broadwater...Cascade...Gallatin...Judith Basin...Madison...
Meagher.

&&

$$

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