Area Forecast Discussion
Issued by NWS Great Falls, MT
FXUS65 KTFX 030541
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1041 PM MST Mon Dec 2 2013
Made some adjustments to snowfall and temps for the overnight period.
The main areas of lift are currently focused over southwest
Montana along an axis of instability and along the US/Canadian
border where relatively warm air in the mid levels was overrunning
the colder air in the low levels. These areas of lift will be slow
to move overnight. Have bumped the snowfall amounts up along the
US/Canadian border and lowered them some over the rest of the
north central Montana, especially for the higher plains near the
Rocky Mountain Front and lower elevation south of the Little Belt
and Big Belt mountains. Lowered temperatures over much of the
plains for tonight. Model guidance continues to run warm, current
observed temperatures over north central Montana are already near
or colder than some of the model forecast overnight lows. Langlieb
A deep upper level low pressure system with an associated arctic
cold front has pushed through Southwest Montana. The push of cold
air will bring snow and gusty winds along with widespread IFR or
LIFR conditions and mountain obscuration. Some improvement will in
conditions will occur Tuesday although widespread MVFR conditions
will continue with local IFR conditions.
/ISSUED 500 PM MST Mon Dec 2 2013/
Today through Tuesday Night...Complex pattern today as advertised
winter weather arrives in central and southwest Montana. A large
scale upper level low is moving through the Pacific Northwest.
Marginal instability beneath this trof has resulted in rain and
snow showers through south central and southwest Montana this
morning. This activity continues to press southward as a strong
cold front advances through north central Montana. Although models
initialized the frontal position well at 12Z and 18Z...in both
instances the front moved faster than guidance. Temperatures
dropped quickly behind the front and will level off in the single
digits tonight and Tuesday. As cold air deepens in increasing upslope
northerly flow, expect widespread snow to develop across region.
Wind gusts to around 40 mph have occurred at stations along the
Rocky Mountain Front with frontal passage. A secondary center of
circulation seen in satellite imagery at 21Z is expected to rotate
around the main upper low and shift south with the deepening cold
air. This feature could create an area of enhanced snowfall
shifting southward overnight. Periods of moderate snowfall will be
expected before tapering late Tuesday. Weather conditions with
snow will include dangerous wind chills and low visibility in
blowing snow. Roads have already iced over and become hazardous.
Wednesday through Monday...From Wednesday at least through the
weekend a strong upper ridge will be in the eastern Pacific which
will keep a cold northwest to north flow aloft over Montana.
Moisture associated with an upper trough over eastern Montana should
lead to isolated to scattered snow showers on Wednesday. Otherwise
expect a mostly dry period with the main threat for snow over the
mountains. Models start to bring some snow to the area by late in
the weekend or early next week but differ on the details. Added a
mention of snow in the forecast for the lower elevations during this
period. The GEM and GFS models bring another surge of cold air into
the area late in the weekend or early next week with the GFS being
quite a bit colder than the GEM. On the other hand the ECMWF does
not show this next cold air invasion. Took a middle-of-the road
.PRELIMINARY POINT TEMPS/POPS...
GTF 3 5 -3 4 / 100 90 50 40
CTB -4 3 -6 2 / 100 80 40 30
HLN 5 11 -1 8 / 100 80 30 30
BZN 5 11 -3 7 / 80 70 30 30
WEY -5 10 -14 4 / 100 40 50 20
DLN 6 11 -4 7 / 90 70 20 20
HVR 6 8 -5 2 / 100 90 60 20
LWT 3 7 -5 4 / 90 90 70 30
WINTER WEATHER ADVISORY until 11 PM MST Tuesday FOR ELEVATIONS
BELOW 6000 FEET FOR Beaverhead...Broadwater...Gallatin...
WINTER STORM WARNING until 11 PM MST Tuesday FOR ELEVATIONS
ABOVE 6000 FEET FOR Beaverhead...Broadwater...Gallatin...
WINTER STORM WARNING until 11 PM MST Tuesday 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.