Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 210513
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1020 PM MST Thu Nov 20 2014

.UPDATE...

No significant changes needed for the evening update. Removed
areas of slight-chance POPS overnight except over the western
mountains. Brisk southwest winds over the north-central plains
will result in a slow rate of cooling toward morning minimum
temps. Patchy fog is possible in portions of Hill and Blaine
counties, but not with enough confidence to include in weather
elements. Nutter

&&

.AVIATION...
UPDATED 0520Z.
Variable mid- and high-level clouds will pass through north-central
and Southwest Montana. Southwest to west surface winds will increase
this evening and remain brisk through the period. The strongest
winds will occur along the Rocky Mountain Front and over adjacent
plains including KCTB. VFR conditions prevail. Nutter

&&

.PREV DISCUSSION...
/ISSUED 425 PM MST Thu Nov 20 2014/

Today through Saturday...A weak shortwave will cross the Rockies and
Central Montana late tonight and Friday while, to the west, a strong
upper level jet will move over the West Coast. A high pressure ridge
over Central Montana will be flattened by a series of shortwaves
ahead of a low pressure trof in the Eastern Pacific. These
disturbances will maintain a lee trof along the slopes of the
Rockies and a strong surface pressure gradient. Winds will remain
brisk through the period across the Rockies and adjacent plains and
become very strong Friday night and Saturday. Winds across Southwest
Montana will not be nearly as strong as those over the plains
although, as the upper level winds strengthen ahead of the
approaching trof, strong winds will also spread across the area
Friday night and Saturday. The trof will be over the Pacific
Northwest by early Saturday morning and good lift will develop ahead
of it across the Rockies. Snow over the Rockies will increase as the
low pressure trof approaches and a winter weather advisory for snow
and blowing snow will be issued beginning Friday night. The upper
level trof will be over the Rockies by late Saturday although the
cold air aloft will still be west of the Rockies. Zelzer

Saturday night through Thanksgiving...Period begins with a mid level
trough moving across MT and surface low pressure tracking east along
and just north of the MT/Canadian border Saturday night. Cold
advection, favorable upper level jet dynamics and slightly
unstable/cyclonic flow aloft will keep a chance for snow showers
across Central/SW MT while moisture wrapping around the low-mid
level circulation center passing by to the north will bring a chance
of snow showers to portions of North Central MT. NW flow aloft
continues Sunday into next week with a period of drier conditions
likely late Sunday through Monday. By Tuesday, flow aloft buckles in
response to shortwave energy coming onshore, allowing the upper
level jet to lift north into the northern Rockies for increasing
chances for precipitation. This is where models begin to diverge
significantly as the ECMWF model brings in a stronger shortwave
trough from the NW, carving out a trough over the interior west with
a much colder Canadian airmass moving into the region Wednesday and
Wednesday night. However the GFS model continues to build upper
level ridging inland Wednesday and Thursday, resulting in a shorter
lived precipitation event with warmer temperatures overall.
Confidence remains low at this point with regard to cold air
intrusion next week, but initial push of moisture/precipitation
Tuesday appears more likely regardless of model solution and have
increased pops that period. Hoenisch

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  32  44  32  44 /   0  10  20  20
CTB  29  42  29  42 /   0  10  20  20
HLN  26  42  29  43 /  10  10  20  50
BZN  18  39  23  42 /  10  10  20  60
WEY  15  31  21  31 /  20  20  50 100
DLN  22  39  27  39 /  10  10  30  60
HVR  25  42  25  42 /   0  10  10  40
LWT  28  45  29  46 /  10  10  10  40

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING until 10 PM MST Saturday Northern Rocky
Mountain Front...Southern Rocky Mountain Front.

WINTER WEATHER ADVISORY from Midnight Friday Night to 5 AM MST
Sunday Beaverhead...Central and Southern Lewis and Clark...
Gallatin...Madison...Northern Rocky Mountain Front...Southern
Rocky Mountain Front.

HIGH WIND WATCH from late Friday night through Saturday evening
Eastern Glacier.

&&

$$

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