Wind Chill Watch 1, NWS Great Falls, MT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
523 AM MST Thu Feb 27 2014

.DISCUSSION...

...Frigid temperatures, wind chills, snow and blowing snow through
the weekend...

Today through Friday...A long-duration winter storm is still on
track to impact most of north-central and southwest Montana with
widespread snow and blowing snow, near record cold temperatures and
frigid wind chills through the upcoming weekend. Numerous Winter
Storm Warnings and Winter Weather Advisories are in effect starting
this evening through Saturday evening. Pacific moisture will
increase across the Treasure State today while a Canadian surface
cold front from Saskatchewan/Alberta descends over the forecast area
this afternoon and evening. Weak shortwave energy and warm air
advection will lead to a chance for precipitation ahead of the cold
front for areas along the Continental Divide and southwest Montana.
Precipitation chances will continue to increase with the cold
frontal passage later this afternoon/evening as moist, westerly flow
aloft overruns an arctic airmass. This overrunning pattern will
persist through the weekend, thus supporting the potential for
widespread accumulating snowfall over much of central and southwest
Montana. The axis of heaviest snowfall will depend on where the cold
front stalls over central or southwest Montana, however latest
forecast models indicate this zone could extend from Helena to White
Sulphur Springs and as far south as Bozeman to West Yellowstone. In
addition to snow, bitterly cold temperatures will return.

Flash Freeze: With high temperatures above freezing today across
southwest Montana ahead of the cold front, a mix of rain and/or snow
will be possible before changing to all snow with the frontal
passage. With the rapid drop in temperatures this evening, a flash
freeze may occur and cause impacts to travel.

Snow: The periods of heaviest snowfall will be tonight through
midday Friday and Friday night through Saturday morning. Total
snowfall amounts through Saturday within the heavy snow axis will
range from 8 to 12 inches with locally higher amounts up to 18
inches in the mountains. Locations north and south of the axis
including the Rocky Mountain Front, adjacent plains, areas along
MT-200 and lower elevations of Beaverhead County, total snowfall
amounts of 4 to 8 inches are expected. Lesser snowfall amounts of 1
to 3 inches are anticipated in area north of MT-200 and along the
Hi-Line. Snow will taper from north to south on Saturday.

Blowing Snow: Gusty northerly winds of 10 to 20 mph with locally
higher gusts will also cause low visibility in areas of
blowing/drifting snow.

Temperature and Wind Chills: High temperatures on Friday will range
from 0 to +10 from I-90 north to the U.S./Canadian border with
readings on Saturday ranging from -15 to 0. Near-record low
temperatures could occur in this same area with overnight lows -15
to -30 and locally colder. With breezy northerly winds, dangerous
wind chill values of -30 to -50 are possible, especially along the
Hi-Line. A Wind Chill Watch is in effect Friday afternoon through
midday Sunday. These extreme cold temperatures will be very
dangerous for pets and livestock. MLV

Saturday night through Thursday...Medium range models remain in
decent agreement to start the period. A closed upper low retrogrades
to western Canada and subsequent west to northwesterly flow aloft
will continue to bring Pacific moisture across the area with
overrunning snow the result. With a fairly deep cold airmass east of
the Continental Divide, snow amounts will decrease on Sunday. The
heaviest amounts will continue over the western and southwest
mountains. Models begin to differ by Monday with the GFS developing
a weak upper ridge over the Pacific Northwest while the European
maintains a westerly flow aloft. Regardless, the circulation around
the closed low over western Canada will continue to bring Pacific
moisture across the area resulting in isolated snow over the plains.
As the closed upper low begins to move eastward once again on
Wednesday, the pattern remains the same with scattered mountain snow
and isolated snow over the plains. The upper low pushes across
northern Saskatchewan on Thursday with rising 500 mb heights over
the Pacific Northwest. Still plenty of moisture moving across the
area from the west coast resulting in isolated snow continuing.
Temperatures will start out bitterly cold with readings Sunday
morning in the minus 20 to minus 30 degree range across central and
northern portions of the county warning area. Readings will slowly
moderate through the week with afternoon temperatures approaching
freezing by Wednesday. Readings will be warmer through the period
over southwest Montana.

&&

.AVIATION...
UPDATED 1220Z.
A Canadian cold front will sweep across the area this afternoon.
Winds behind the front will become northerly and may be gusty for s
few hours. Snow will develop behind the front as moisture from the
southwest overruns the cold air accompanying the front. VFR
conditions prevail through 20z but will begin to deteriorate
thereafter. Widespread MVFR/IFR conditions will develop after 00z
due to low ceilings, snow, and blowing snow. MVFR/IFR conditions
will persist beyond 12z. Mountains will become obscured after 00z.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  37  -1   2 -22 /  30  90  90  80
CTB  34  -6  -2 -28 /  20  70  80  60
HLN  33   8   9 -13 /  60  90  90  90
BZN  34  12  16 -11 /  60 100 100  90
WEY  35  26  35   8 /  60 100 100 100
DLN  35  20  26  -2 /  80  90  70  90
HVR  27  -2   3 -25 /  10  50  50  30
LWT  36  -2   0 -23 /  40  90  90  80

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
WINTER STORM WARNING from 6 PM this evening to 6 PM MST Saturday
Broadwater...Central and Southern Lewis and Clark...Gallatin...
Jefferson...Madison...Meagher.

WIND CHILL WATCH from Friday morning through Sunday morning
Blaine...Cascade...Central and Southern Lewis and Clark...
Chouteau...Eastern Glacier...Eastern Pondera...Eastern Teton...
Fergus...Hill...Judith Basin...Liberty...Meagher...Northern
Rocky Mountain Front...Southern Rocky Mountain Front...Toole.

WINTER WEATHER ADVISORY from 6 PM this evening to 6 PM MST
Saturday Beaverhead...Chouteau...Eastern Glacier...Eastern
Pondera...Eastern Teton...Northern Rocky Mountain Front.

WINTER WEATHER ADVISORY from 6 PM this evening to 6 PM MST
Saturday FOR ELEVATIONS BELOW 5000 FEET FOR Cascade...Fergus...
Judith Basin...Southern Rocky Mountain Front.

WINTER STORM WARNING from 6 PM this evening to 6 PM MST Saturday
FOR ELEVATIONS ABOVE 5000 FEET FOR Cascade...Fergus...Judith
Basin...Southern Rocky Mountain Front.

&&

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