Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 070403
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
903 PM MST Tue Dec 6 2016

.UPDATE...

The tail end of a weak upper level disturbance skirting southwest
MT is moving into Wyoming. Snow flurries remain possible over this
area through much of the night. Surface high pressure over North-
central MT is now over 1040 mb and climbing as the Arctic air mass
continues to deepen. Will maintain mid-level clouds and isolated
flurries over this area tonight, but not expecting any new snow
accumulation. The headline concern is wind chill temperatures
dropping below -20F tonight. Nearly all locations in the CWA
indicate present temperatures in the single digits above and below
zero. Wind chill temperatures are in the teens below zero at
several locations and a few have already dipped below -20F where
wind speeds are around 10-15 mph. Although some areas will
continue to have light winds below 10 mph as high pressure settles
in, will maintain the wind chill advisory to advertise the cold.
Freshened the overnight forecast to match observed trends, but
otherwise looking in good shape. PN

&&

.AVIATION...
Updated 2345Z.

Upper level trough remains over region for continued northerly flow
aloft with cold surface high pressure system movings southward from
Canada. Low- to mid-level clouds producing MVFR/VFR conditions
prevail but areas IFR due to low clouds and flurries can also be
expected at times. Models suggest partial clearing possible at
times...especially after 12Z Wednesday. mpj

&&

.PREV DISCUSSION...
/ISSUED 445 PM MST Tue Dec 6 2016/
Tonight through Thursday...A few light snow showers are moving
across Central/Southwest MT, but the activity is fairly
light/scattered. Most of the snow showers will end this evening,
with any snow accumulations generally less than a quarter of an
inch. Expect mostly dry conditions Wednesday/Wednesday night as we
are in between systems. The next upper level disturbance will
approach the Rocky Mountain front/Southwest MT by late Thursday
afternoon...with the bulk of the snowfall auguring Thursday
night/Friday. It will be very cold the next few nights, especially
in areas that have some clearing/snow cover. For now I leaned
closer to the colder GFS numbers. Wind chill advisory in effect
for the entire region tonight/Wednesday morning. The wind chill
advisory will likely be extended into Thursday for portions of
the region tomorrow. Brusda

Thursday night through Monday...A high pressure ridge over Central
and Southwest Montana will be flattened Thursday night as a low
pressure trof moves over the West Coast. Moisture ahead of this trof
will cross the Rockies and bring cloudy skies with increased chances
of precipitation. Snow accumulations will mainly be over the western
mountains. Weak high pressure will build again Friday but another
disturbance moving through the flow aloft from the west will
increase the chances of snow again Friday night and Saturday. As
this trof crosses the zones, the associated cold front will bring
another push of cold air into the region. This will keep
temperatures, especially across the northern tier, well below
normals Saturday and Sunday. Weak high pressure will build again
Saturday night and most snow will be limited to higher elevations.
However, another shortwave will be upstream and periods of light
snow will continue Sunday night through the end of the period. Cold
temperatures will continue through the extended forecast period,
especially across the northern half of the forecast area where
temperatures will generally remain 15 to 20 degrees below normals.
Southwest Montana will not be affected as much by the Canadian
air and temperatures will push upwards towards normals.
Zelzer

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF -10   0 -10   3 /  20  10  10   0
CTB -11   0 -13  -3 /  10  10  10  10
HLN  -9   5  -5  17 /  20  10   0  10
BZN  -8   2  -8  17 /  20  10   0  10
WEY -12   6 -14  15 /  30  20  10  20
DLN  -7   8  -4  18 /  20  10   0  40
HVR  -7   2 -10   0 /  10  10  10  10
LWT -11   0 -11   6 /  20  10  10   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Wind Chill Advisory until noon MST Wednesday Blaine...
Broadwater...Cascade...Central and Southern Lewis and Clark...
Chouteau...Eastern Teton...Fergus...Hill...Jefferson...Judith
Basin...Meagher...Southern Rocky Mountain Front.

Wind Chill Advisory until noon MST Wednesday Eastern Glacier...
Eastern Pondera...Liberty...Northern Rocky Mountain Front...
Toole.

Wind Chill Advisory from midnight tonight to noon MST Wednesday
Beaverhead...Gallatin...Madison.

&&

$$

weather.gov/greatfalls



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