Area Forecast Discussion
Issued by NWS Great Falls, MT

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110
FXUS65 KTFX 021800
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1100 AM MST Fri Dec 2 2016

.UPDATE...

The current forecast handles the rest of today well, so no major
changes were needed for the update this morning. The s/w moving into
British Columbia at this time will flatten the ridge over the
Pacific NW. This, in turn, will bring increasing winds aloft and at
the SFC later today through tonight, especially along and east of
the Rocky Mtn Front. For now, still thinking wind gusts will remain
below High Wind Criteria level tonight along the Rocky Mtn Front,
but we`ll re-evaluate this once the latest 12z guidance comes in
to determine if a High Wind Warning is needed. Regardless, 50-60+
mph winds will be possible right along the Front tonight, with
lower gusts out over the plains. Precip-wise, still looks like
most rain/snow showers will be confined to the western/southwestern
mountains through this afternoon as downsloping should limit
precip in the plains/valleys.

Of note, lingering snow from last night across central Montana will
continue to be responsible for slick spots on some roads, but
mostly sunny skies combined with temperatures rising above
freezing later today should allow for improved road conditions by
this afternoon. Martin

&&

.AVIATION...Updated 1145Z.

Central and Southwest Montana will be underneath a building ridge
today. However, a low pressure shortwave will flatten this ridge and
bring a chance of snow across the region again Friday night. Local
MVFR/IFR conditions are expected near snow showers. In addition,
mountain obscuration is possible across the region during the night.

&&

.PREV DISCUSSION...
/ISSUED 445 AM MST Fri Dec 2 2016/

Today through Sunday...A weak disturbance is currently causing
light snow across central portions of the CWA...while snow is on a
diminishing trend elsewhere. Continued the Winter Weather
Advisories across the central areas...while expiring the
remainder. The morning commute could be slick across anywhere that
receive fresh snow overnight...those traveling should use caution.
High pressure ridge very briefly builds into the region this
morning...ending snow across much of the area by the mid to late
morning hours. This ridge then gets washed out later today through
this evening...bringing an increased westerly flow...and perhaps a
few mountain snow showers to the west. Tonight into Saturday
morning a weak disturbance in the westerly flow moves through the
region bringing more showers to the west and south...with breezy
to windy conditions starting to develop elsewhere. Through
Saturday morning this disturbance...combined with increased
moisture...could even bring a few widely scattered snow showers to
the lower elevations...with little impacts expected. Mainly
mountain snow showers...with a few lower elevation snow
showers...will then be possible for much of the day Saturday into
Saturday evening. The increased westerly flow could also bring
breezy to windy conditions to much of the CWA. 700 MB winds still
aren`t as impressive as previous model runs. So while windy
conditions are possible...High Wind Criteria still looks to not be
met at this point. Our focus then shifts to the impending winter
system on Sunday. Flow flattens Saturday night and brings moist
westerly flow to the western and southern portions of our CWA.
This will provide for decent chances of mountain snow
showers...with windy conditions elsewhere. Models indicate that
this westerly flow may cause dry downsloping to start the day
Sunday...possibly delaying the start of snow for the lower
elevations. However...once the trough moves across Canada Sunday
afternoon...our flow becomes more southwesterly and even more
moist. Then the disturbance and a cold front will progress across
the region later Sunday afternoon. So current timing with the
advertised winter storm looks to be western and southern mountains
Saturday night into Sunday morning...then widespread snow
spreading to the lower elevations Sunday afternoon...and
continuing onward from there in the long term period. A lot of
timing and track details are still needed to be worked out...as
well as assessing the strength of dry downsloping ahead of the
storm. Will hold off on any highlights for this shift...but make
sure to check back for updates. Temperatures appear to be near
normal in the 30s and low 40s for the short term...although fresh
snowfall could cause slightly cooler temps at times. Anglin

Sunday night through Thursday...The extended period begins with a
rather broad trof across the western US. A shortwave moving through
the strong, generally west flow aloft will continue the widespread
precipitation. Significant accumulations are expected especially at
higher elevations. A cold front associated with the shortwave will
cross the Rockies Sunday night and begin a period with temperatures
much cooler than seasonal normals. The trof across the west will
continue to deepen and slow Monday and Tuesday. However, dynamics
will be to the south and precipitation may be light or intermittent.
The trof will move east of the zones Wednesday. However, the ECMWF
is slower than the GFS with this movement. Thus, the ECMWF holds low
pressure over the zones longer than the GFS. Do not have a preferred
solution at this time so Will blend this period. As the high
pressure builds,  Central and Southwest Montana will remain
underneath unsettled northwest flow aloft and a chance of snow will
continue. The air mass will begin to trend warmer Wednesday night as
the high pressure builds. However, moisture moving underneath the
ridge will keep at some showers over the region, mainly the western
mountains and Southwest Montana. The chance of showers will increase
Thursday as moisture ahead of another to the west moves on shore.
Zelzer

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  37  30  41  31 /  30  20  10  10
CTB  37  26  38  28 /  10  20  20  10
HLN  38  24  41  26 /  20  20  20  20
BZN  33  21  36  25 /  20  20  30  30
WEY  24   8  24  15 /  10  20  40  40
DLN  31  20  35  22 /  10  10  20  20
HVR  38  27  40  27 /  10  30  20  10
LWT  36  27  39  27 /  30  20  20  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

weather.gov/greatfalls



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