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000
FXUS65 KTFX 122353
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
450 PM MST Thu Dec 12 2013

UPDATED AVIATION SECTION

.DISCUSSION...

Tonight through Saturday...Strong and gusty winds will continue
this evening as the combination of weak energy and westerly mid-
level flow promotes downslope winds over the Rocky Mountain Front
and adjacent plains. Will continue the High Wind Warning through
11 pm MST for the Rocky Mountain Front with wind gusts up to 60kts
at times. Another upper-level low will cross into the Treasure
State on Friday and as Pacific moisture increases over western
Montana, light snow will develop in the higher elevations of the
Rocky Mountain Front and central mountains by the afternoon. Snow
accumulations of 1 to 3 inches are possible in the mountains. High
temperatures on Friday will be slightly cooler under northwest
flow aloft with readings in the 30s. Southwest winds will increase
Friday night with warmer air spreading into the area. Weak
overrunning may support isolated snow showers Friday night and
have added a slight chance of pops. By Saturday, increasing west-
southwest winds are expected with a tightening pressure gradient
as an upper-level shortwave trough approaches. This gradient will
support strengthening downslope winds on the lee side of the
Rockies with wind gusts approaching 60kts by Saturday afternoon.
High wind highlights may be needed during this time frame and will
continue to monitor. MLV

Saturday night through Wednesday...
A high pressure ridge will be over the Pacific Northwest Saturday
night and the zones will be underneath northwest flow aloft. A
disturbance moving across the top of the ridge will deepen the
surface pressure trof along the lee of the Rockies. Strong and gusty
winds will develop, and winds could be strong enough to require high
lights. Low pressure over the Gulf of Alaska will move east and
flatten the ridge. Several disturbances will move through the flow
aloft and the air mass will remain unsettled although, in general,
conditions across central Montana will remain dry through Sunday
night. The best chance for precip will once again be over the
Northern Rockies where west to northwest flow aloft will keep at
least a good chance of snow over the continental divide. The upper
level low will continue to move east into central Canada and an
associated cold front will move south across the Canadian border
late in the forecast period. The models begin to diverge somewhat on
their solutions by Monday. The ECMWF deepens the trof over the Gulf
of Alaska more than the GFS and produces a sharper ridge over the
West Coast. This ridge eventually moves over the zones Tuesday while
the GFS keeps the region cooler and under unsettled northwest flow.
Despite the differences, both models develop a low pressure trof
over the West Coast by Wednesday. Although the differences lower the
confidence for daily temps and weather in this timeframe, the
development of the trof adds confidence to the continued southward
movement of the cold Canadian air mass. Colder air will remain to
the north and finally push south towards the border Wednesday as a
low pressure trof moves across the Pacific Northwest and approaches
the Rockies. The approach of this trof will bring moisture into the
area and widespread precipitation as the associated cold front moves
into the zones. Temperatures will begin the period above normals.
Warmest temps will occur Sunday before beginning to trend downwards.
By Tuesday, below normal temps will again be moving south through
the region with very cold temperatures again moving into the
northern zones by Wednesday night. Zelzer

&&

.AVIATION...
UPDATED 2350z.
West to northwest flow aloft will continue as an upper level
disturbance approaches western Montana. Mid and high clouds will
increase overnight ahead of the disturbance aloft. Surface winds
remain gusty along the Rocky Mountain Front and adjacent plains but
will decrease overnight. Mountain snow showers will develop after
17z. VFR conditions prevail with MVFR conditions possible in the
vicinity of snow showers.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  23  36  23  44 /  10  20  20  10
CTB  15  34  20  43 /  10  20  20  10
HLN  18  34  21  39 /  10  20  20  10
BZN  12  33  14  35 /  10  30  30  10
WEY   1  25   2  23 /  20  40  40  30
DLN  12  32  14  36 /  10  20  20  10
HVR  10  24   7  37 /  10  20  20  10
LWT  20  37  19  43 /  10  20  20  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING until 11 PM MST this evening Northern Rocky
Mountain Front...Southern Rocky Mountain Front.

FLOOD ADVISORY until further notice for the Gallatin River near
Gallatin Gateway.

&&

$$


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