Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 211755
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1055 AM MST Sun Dec 21 2014

...UPDATE TO AVIATION...

.UPDATE...

MDOT highway cams reveal snow falling over area mountain passes
with reduced visibility as forecast. This snow will continue
through the day. Light freezing rain has been reported in Ft.
Belknap southeast of Havre. Light rain showers over this area
continue to move east with temperatures rising above freezing, so
expect this hazard to end by 11am. Wind gusts along the Rocky
Mountain Front are just now exceeding 60mph. Surface pressure is
beginning to rise along a line from Cut Bank to Great Falls to
Helena. Expect wind gusts to increase with these pressure rises
along the Rocky Mountain Front, then expand eastward into Central
Montana through the afternoon. HRRR guidance for wind gusts
supports strengthening wind gusts today. High wind warnings and
winter weather advisories for mountain snowfall remain in effect.
Updated temperatures and winds forecast for today to align closer
with observed trends. Nutter

&&

.AVIATION...
UPDATED 1755Z.
A strong and unsettled northwesterly flow aloft is propelling a
surface cold front through central Montana at this hour. Isolated to
scattered rain and freezing rain showers ahead of the front will
move into eastern Montana by 20Z. Behind the front, gusty winds and
isolated showers will continue over the plains and in the valleys
through 00Z Monday. However, the western and southwest mountains
will continue to see widespread snow, blowing snow and obscurations
through the period. Strong winds aloft will continue to fuel
mountain wave turbulence to the lee of north-south oriented mountain
ranges as well as low level wind shear. Eastern slopes of the
Rockies can anticipate local wind gusts in excess of 70 mph at times
through this afternoon. mpj

&&

.PREV DISCUSSION...
/ISSUED 438 AM MST Sun Dec 21 2014/

Today through Tuesday...Strong west to northwest flow aloft today. A
shortwave will move through this flow and keep winds very strong.
Radar shows light precip over the western mountains. This
precipitation will spread east this morning as a low pressure
shortwave and associated cold front cross the Rockies. A surface low
pressure trof is over the CWA with higher pressure over Western. The
NAM gives 40 kt winds at just above the boundary level through the
day. Due to the position of the jet and timing of the front, will
cancel the current high wind watch but issue a warning for Lewis and
Clark, Cascade, Chouteau, Judith Basin, and Fergus counties. The
period of strongest winds will be associated with the frontal
passage. Will start Lewis and Clark warning with the issuance of
this forecast package, and start the others at 18z. The jet over the
Rockies will gradually shift to a more northwest direction during
the night. A ridge will build over the Eastern Pacific and northwest
flow aloft will be over the zones Monday. This ridge will be over
the Pacific Northwest by early Tuesday morning and move over the
zones during the day. The airmass will remain dry underneath the
high pressure but also remain rather cool. Zelzer

Tuesday night through Sunday...Expect another Pacific storm system
to move through the region from Tuesday night through Christmas Day.
Precipitation will be light to start with Tuesday night into
Wednesday morning...but will pick up in intensity by late Wednesday
afternoon through Christmas morning. It still looks like the swath
of heaviest snowfall will fall west of a line from Cut Bank to
Lewistown...with the Havre area only seeing around an inch of snow.
Otherwise...overall total snow accumulations still look to be on
track from previous forecasts...with a slight increase in the
mountains. Thus a generally 2 to 5 inches is expected at lower
elevations and 6 to 12 inches is expected in the mountains. Isolated
amounts around 16 inches will be possible in the mountains.
Temperatures will be mild Wednesday morning...but will fall rather
quickly Wednesday afternoon as colder air moves into the region
changing any rain back over to snow. For Friday and Saturday...it
will generally be cold with just a passing snow shower from time to
time. For Sunday and into early next week...the GFS13 and EC are
quite different. The EC model wants to start slowly warming things
up with little precipitation...while the GFS13 wants to bring down
significantly colder air and a better chance for precipitation. For
now I will go in the middle...but changes in the forecast are likely
to occur for this time period once model agreement starts to become
a bit more clear. Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  47  30  39  20 /  40  20  20  20
CTB  43  27  37  20 /  30  20  10  10
HLN  45  29  37  16 /  80  30  30  20
BZN  42  24  33   8 /  70  40  40  20
WEY  38  21  31   4 / 100  80  50  30
DLN  44  28  35  12 /  80  50  30  10
HVR  44  28  40  20 /  90  40  30  20
LWT  47  29  37  19 /  80  40  30  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING until 5 PM MST this afternoon Central and
Southern Lewis and Clark...Northern Rocky Mountain Front...
Southern Rocky Mountain Front.

WINTER WEATHER ADVISORY until 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.

WINTER WEATHER ADVISORY until 5 AM MST Monday FOR ELEVATIONS
ABOVE 5500 FEET FOR Beaverhead...Broadwater...Cascade...
Gallatin...Judith Basin...Madison...Meagher.

HIGH WIND WARNING until 10 PM MST this evening Cascade...
Chouteau...Fergus...Judith Basin.

&&

$$

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