Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 122338

Area Forecast Discussion
National Weather Service Great Falls MT
438 PM MST Thu Jan 12 2017

Updated Aviation Discussion


Tonight through Saturday...A relatively dry northwest flow aloft
will keep the forecast area mostly clear through Saturday, but
westerly winds will be gusty at times, mainly over the plains of
North Central and Central Montana. Winds have been gusty between
40 and 60 mph already along the Rocky Mountain Front, causing
widespread visibility-reducing blowing snow. As the surface trough
to the lee of the Rockies spreads east overnight, gusty westerly
winds will overspread the plains as well. Although gusts there
will not be quite as strong (mostly 35 to 45 mph), loose
relatively freshly-fallen snow will be easy to lift. Have
therefore expanded the Advisory for blowing snow east across the
Hi-Line to the Sweetgrass Hills, south along the plains adjacent
to the Rocky Mountain Front, and east from Great Falls to
Lewistown. Have also kept the expiration time the same (8 am
Friday). Will see how the winds react to the current snowpack
before deciding on whether or not to expand this Advisory farther
east. Late Friday morning through the overnight hours, winds will
generally decrease. A weak disturbance in the flow aloft may bring
gusty westerly winds back to the plains on Saturday. The
temperature forecast will be somewhat tricky over the next couple
of days, as the gusty winds could cause rapid warmups, but
lingering snowpack could hinder such warmups. Have kept
temperatures cooler than model guidance in the more wind-protected
Southwest Montana valleys, which could cause very cold overnight
temperatures due to the clearing skies. Warmer temperatures are
expected closer to the east slopes of the mountains. Overall,
though, temperatures will remain cooler than normal.

Saturday night through Thursday...A generally dry and breezy
pattern to transition into more active...but
Saturday night will start with a weak shortwave traversing across
the moisture will allow for mainly dry
conditions with a few clouds. Sunday through Monday we then find
ourselves in northwest flow with limited moisture and weak
disturbances at times. Little sticks out as a potential weather
maker so continued dry condtions...with only a few isolated snow
showers across the western mountains. Each weak disturbance Sunday
through Monday does bring an increased gradient at
times...providing for some breezy winds. Nothing looks high wind
at this point...but if a loose snowpack continues...blowing and
drifting snow will be possible. Tuesday through the rest of the
work week we then see a potential development of an atmospheric
river similar to the previous weeks active weather...with breezy
winds at times. The main difference with this new feature is the
amount of warm air associated with the mentioned feature. 700 mb
temps hover around the -6 to -10 C range during the event...with
breezy downsloping air bringing the 800 mb temps above 0 at times.
The result of all this warm air could be a messy mix of
rain...freezing rain...and perhaps some snow at times...across the
lower elevations as multiple disturbances and increased moisture
push through the area next week. Used model soundings and 800 mb
temps to try and include mention of this wintry
mix...however...confidence remains low on timing and locations at
this point...except across the south where mainly snow is
expected. With all this warm air...high and low temperatures will
be on the rise throughout the long term period. Models indicating
highs in the low to mid 40s possible by mid next week...with lows
in the 20s to even 30s. It will be interesting to see if the warm
air can overcome the recent snowfall. For now bumped down temps
slightly to account for snowcover. If we can get prolonged periods
above freezing...and combine that with the potential for rain
showers...there is a chance localized flooding is possible next
week due to quickly melting snow and perhaps ice jams. Be sure to
check back on the latest forecasts. Anglin


Updated 2338Z.

Area remains under a dry NW flow aloft through Friday with surface
high pressure centered over western and SW MT and in the Dakotas
while a surface trough develops along the east slopes of the
Rockies. Clear skies and light winds will prevail across SW MT
terminals, though some patchy fog cannot be ruled out for a period
tonight. To the north, breezy SW surface winds will expand eastward
across the plains tonight. Strongest winds will be concentrated
along and adjacent to the Rocky Mtn Front where blowing snow may
reduce surface visibility at times as far east as the KCTB terminal.


GTF  10  28  11  30 /   0   0   0   0
CTB   6  26   5  28 /   0   0   0   0
HLN  -5  16   1  24 /   0   0   0   0
BZN  -5  17  -3  24 /   0   0   0   0
WEY -11  17 -14  21 /   0   0   0  10
DLN  -5  18   0  26 /   0   0   0   0
HVR  -7  18  -3  22 /   0   0   0   0
LWT  10  28   8  31 /   0   0   0   0


Winter Weather Advisory until 8 AM MST Friday Cascade...Eastern
Glacier...Eastern Pondera...Eastern Teton...Fergus...Judith

Winter Weather Advisory until 8 AM MST Friday Northern Rocky
Mountain Front...Southern Rocky Mountain Front.


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