Area Forecast Discussion
Issued by NWS Great Falls, MT
FXUS65 KTFX 021739
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1035 AM MST Mon Dec 2 2013
Cold front as of 16z has moved south to a line from Conrad to Fort
Benton and Havre. Web cams indicate snow fall developing behind
the front. Will have to monitor for possible local near blizzard
conditions developing for a few hours after frontal passage. The 12z
NAM initialized the frontal position well, but already appears
just a bit slow. Will expect the front through Great Falls approx
1730 UTC, and Bozeman to Lewistown approx 21z. Snow will steadily
develop behind the front as upslope flow deepens. The airmass
south of the front is marginally unstable with lowering heights
and weakly divergent flow aloft. Models suggest a band of heavier
precipitation may develop along a line from Butte to Lewistown.
Although mainly rain at lower elevations, this could produce a
period of heavy mountain snow this afternoon. Update forthcoming
to adjust temperatures and weather associated with frontal position.
A potent Canadian cold front had passed through KGTF as of 1730z and
will reach KHLN and KLWT between 18z and 20z and KBZN between 22z
and 00z. Widespread IFR conditions with occasional LIFR conditions
are expected by later this afternoon with moderate, possibly heavy
snow and low vis less than 1 mile at times over the north-central
plains. Across southwest Montana including KHLN and
KBZN...widespread MVFR with occasional IFR conditions are expected
once the front pushes through these areas. Rain, snow showers and
ice pellets are likely along and ahead of the cold front, but
precipitation will quickly changeover to all snow as temperatures
rapidly fall below freezing. Precipitation early this afternoon
will be more convective as morning sunshine causes the atmosphere to
destabilize. The unstable conditions will lead to the periods of
mixed precipitation before changing to all snow. Strong northerly
winds will also cause areas of blowing snow, which could further
reduce visibility less than one-half mile at times. Mountains will
be completely obscured over the next 24 hours. MLV
/ISSUED 500 AM MST Mon Dec 2 2013/
Today through Tuesday Night...Moisture ahead of an approaching
Pacific weather system will continue to bring snow, heavy at
times, to the mountains of western and central Montana through
tonight. Snow there will decrease Tuesday into Tuesday night as
the system exits the area. This system will drag a strong cold
front south from the Canadian border (where it is currently)
through north central Montana by early afternoon, then through
southwest Montana by early evening. Gusty westerly winds will
shift northerly behind the front, bringing winds of 15 to 25 mph
with gusts as high as 40 mph to the area. Strong lift and
instability will initially be associated with the frontal
passage. Then, more sustained (though a bit weaker) lift will move
into the area overnight into Tuesday due to deepening of the
northerly upslope flow as the system begins moving east of the
area. These features will cause snow to be heavy at times, causing
reduced visibility in blowing snow and adding snowpack onto icy
roads (due to rapidly cooling temperatures). Am therefore
continuing the Winter Storm Warnings for all elevations of north
central Montana and elevations above 6000 feet in southwest
Montana, with Advisories for lower elevations there (for lower
expected snowfall amounts). Mountains will generally receive an
additional 8 to 16 inches. The plains of north central Montana will
likely see 5 to 9 inches, while the valleys of southwest Montana
will receive 2 to 4 inches. Temperatures will also rapidly fall
behind the cold front today and tonight, bringing single digit
highs for Tuesday and lows possibly as low as 10 below zero for
Tuesday night. Overall, though, winds and snow should decrease
Tuesday afternoon through Tuesday night.
With regards to the High Wind Warnings for portions of north
central and southwest Montana, strong winds have not developed
there as previously expected, so have canceled those warnings.
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 approach to temperatures with these different
.PRELIMINARY POINT TEMPS/POPS...
GTF 39 2 2 -8 / 60 100 90 50
CTB 29 -4 0 -11 / 100 100 70 40
HLN 43 4 6 -7 / 60 100 50 30
BZN 45 3 8 -9 / 80 70 50 30
WEY 35 -7 5 -20 / 100 100 40 50
DLN 45 5 9 -8 / 80 70 40 20
HVR 29 6 6 -11 / 90 100 90 60
LWT 39 1 4 -11 / 60 100 100 70
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.