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National Weather Service Great Falls MT
1100 AM MST Sat Dec 3 2016

Aviation Section Updated

.UPDATE...

The main changes for the update this morning were to adjust wind and
pops based on current obs/trends. Downsloping is really limiting
precip east of the Rockies at this time and pops were adjusted to
reflect this. Satellite/radar show a few light showers from Havre
south through Lewistown and left low-end pops there. Otherwise, most
of the shower activity through this evening should be confined to
the mountains. Regarding the wind, the SFC pressure gradient should
gradually relax some compared to last night and this morning with a
gradual decrease in the wind expected along/east of the Rocky Mtn
Front today. However, strengthening winds aloft later today and
tonight should still be able to mix down to the SFC at times,
especially central Montana, so it will still remain breezy/windy at
times. As for the current Winter Storm Watch, am going to wait for
the latest data to come in to make a final call on any upgrades, so
stay tuned this afternoon for updates on advisories/warnings.
Martin

&&

.AVIATION...
Updated 1800Z.
Scattered snow showers will continue along the Rocky Mountain Front
and across Southwest MT today, while breezy west winds allow for
mostly sunny skies over the Northern Plains. Winds will diminish
this evening as clouds increase, especially after 07z Sunday.
Widespread snow will start to develop after 18z Sunday along with IFR
conditions. Otherwise, mostly VFR conditions will prevail before
18z, but some mountains/passes will be obscured with the snow
showers this afternoon. Brusda

&&

.PREV DISCUSSION...
/ISSUED 427 AM MST Sat Dec 3 2016/

Today through Monday...Initial disturbance that brought a few
light snow showers yesterday evening has moved off into eastern MT
early this morning...leaving behind breezy conditions...and only
a few isolated to widely scattered snow showers. Another weak wave
and push of moisture may bring a second shot of scattered snow
through the morning and afternoon hours today with the best
chances coming across western...southern...and central portions.
Strong winds will again be possible today with a developing strong
jet and pressure gradient. Gusts still look to be below high wind
criteria...however...winds over 50 MPH along the Rocky Mountain
Front...and 30-40+ MPH elsewhere are possible. We then see the
development of a sfc low and strong moist westerly flow aloft
tonight. With will provide for continued strong winds...with some
more scattered snow showers. 

Sunday into Monday still looks to see the return of winter
conditions. Upper level trough...sfc low...cold front...and
favorable jet dynamics all look to come together and bring
widespread snow during this time period. Intensity...timing...and
accumulations are still at medium confidence. GFS and Euro models
showing similar timing with moist sw flow bringing an initial wave
of snow to the west and south Saturday night through Sunday
morning...with the strong flow possibly causing downsloping delays
for central and eastern portions. However...by Sunday afternoon
this disturbance begins to progress across Montana spreading snow
to most locations by the late evening hours. Snow then continues
for Sunday night into Monday morning. The wave then kicks into the
Northern Plains Monday afternoon...however lingering moisture and
nw flow may still provide for a few scattered snow showers through
the day Monday. Confidence still remains only moderate...as some
model runs...such as the NAM...are trying to split the wave and
allow downsloping air to hinder snow. Stuck with a mainly GFS and
Euro blend for the time being. Winter Storm Watches were kept the
same...with the Rocky Mountain Front starting after 06Z Sunday and
the remainder of the highlights after 18z Sunday. Initial snowfall
forecasts have 1 to 2 feet in the Rocky Mountain Front...2 to 6
inches across the lower elevations of the CWA and 4 to 8 inches
across the southern mountains. Be sure to check back for the
latest updates. Temperatures will remain near normal for today and
Sunday...then quickly dropping on Monday with the push of arctic
air. With fresh snow...and new snow forecasted...combined with
breezy to strong winds at times...areas of blowing snow are also
possible throughout the short term period. Anglin

Monday night through Friday...Strong west flow will be moving
through a broad trof over Central and Southwest Montana. Cold air
will be settling into the zones and the Tuesday morning lows will be
much colder than the previous day. This will begin a period, lasting
through the remainder of the forecast period, where temperatures
will be well below seasonal normals. High pressure will already be
building aloft Monday night and Tuesday although the flow aloft will
be unsettled and scattered snow showers will remain over higher
elevations. The high pressure will continue to build Tuesday night
and Wednesday, and the air mass will continue to dry. Temperatures
will remain cold and, with snow on the ground and clearing skies,
very cold temperatures are expected Tuesday and Wednesday mornings.
The ridge of high pressure will be building over the zones Wednesday
night and Thursday. This will begin a gradual warming of the air
mass although temperatures will be slow to recover and remain 5 to
10 degrees below normals Friday. Zelzer

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  39  31  40  16 /  20  20  30  70 
CTB  37  29  36  10 /  10  20  40  50 
HLN  40  24  41  17 /  20  20  30  40 
BZN  35  24  37  15 /  30  20  30  50 
WEY  24  15  28   6 /  50  60  60  70 
DLN  35  22  36  12 /  20  10  40  50 
HVR  39  28  38  16 /  30  10  30  40 
LWT  36  27  38  15 /  30  20  30  60 

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Sunday morning through Monday afternoon 
Beaverhead...Broadwater...Cascade...Central and Southern Lewis 
and Clark...Eastern Glacier...Eastern Pondera...Eastern Teton...
Fergus...Gallatin...Jefferson...Judith Basin...Madison...Meagher.

Winter Storm Watch from this evening through Monday afternoon 
Northern Rocky Mountain Front...Southern Rocky Mountain Front.

&&

$$

weather.gov/greatfalls

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