Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 271804
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1105 AM MST Mon Feb 27 2017

Aviation Section Updated

.UPDATE...
1100 AM Update...Dropped the advisory for Southwest MT. Widespread
impacts are no longer expected. Brusda

1000 AM Update....Updated forecast is out. Winter Weather Advisory
for Central/North Central MT has ended. Just a small chance for a
passing light snow shower in this region. Over Southwest MT...1 to 3
inches of snow is possible...mostly at higher elevations. Thus the
highlight might end early in this region as well. Otherwise the rest
of the forecast for today is on track. Brusda

&&

.AVIATION...
UPDATED 1805Z.
Low clouds/patchy fog in the Cut Bank area should dissipate by 21z.
Otherwise...partly cloudy skies this afternoon will give way to a
few scattered snow showers...mostly over Southwest MT and the Rocky
Mountain Front. Expect another chance for snow showers on Tue
morning...mainly after 13z to spread from west to east through the
region. Some mountains will be obscured at times through the
period. Brusda

&&

.PREV DISCUSSION...
/ISSUED 500 AM MST Mon Feb 27 2017/

Today through Wednesday....Satellite imagery and analysis this
morning shows a broad upper level trough remains across region with
shortwave in its base currently moving east across southern ID while
additional energy dives south along the BC Coast. Light snow
continues across much of North central MT in lingering upslope flow
but intensity has decreased and will continue to gradually decrease
through the rest of this morning. Snow showers also continue along
the ID border with incoming shortwave energy there and will likely
persist through this afternoon. Shortwave energy upstream along the
BC coast will rotate through the Northern Rockies later tonight
through Tuesday for additional snow showers with temperatures
remaining below seasonal averages. Drier conditions move in Tuesday
night before another round of shortwave energy in fast NW flow aloft
moves into the region Wednesday with snow showers again
redeveloping. Trough of low pressure at the surface develops along
the east slopes of the Rockies Tuesday night with surface low
tracking east along the US/Canadian border Wednesday afternoon.
Winds increase initially along the Rocky Mtn Front Tuesday night
with gusty SW to W winds spreading S and E across the Forecast area
Wednesday morning, shifting to NW Wednesday afternoon as the surface
low moves off to the east. Hoenisch

Wednesday Night through Monday...The medium/long range period starts
with NW flow aloft, but shifts to an active zonal flow by late in
the week. Models appear to be in decent agreement initially, but
begin to diverge late in the week and over the weekend. The extended
period was primarily a blend of the ECMWF/GFS as the CMC appears to
be more of an outlier at the moment. Overall, I would say confidence
in the extended period is a bit below average.

Where confidence is highest is with the potential for stronger
winds. That said, there are still enough differences to keep
confidence somewhat lower. For now, it appears the best chance of
seeing strong winds will be late Thursday through Friday night.
Strengthening winds aloft with the zonal flow plus a tightening
pressure gradient within a developing lee-side SFC trough should
lead to stronger winds first along the Rocky Mtn Front, then
potentially out across much of the plains. Over the plains, the
models differ on how strong the winds will be just above the SFC and
how much mixing will occur which leads to uncertainty regarding how
strong the winds will be. Given the uncertainty, and a trend in the
models to back off the wind just a bit, I have lowered winds/wind
gusts just a bit in the THU/FRI period. However, this period will
continue to be monitored for potential high wind highlights if
confidence increases. Across the mountains of SW MT, much of the
extended period will likely feature breezy/windy conditions at times.

Precip-wise, the zonal flow will mainly favor the
western/southwestern mountains initially. However, the models are
forecasting a 140kt jet to move over Montana over the weekend. While
moisture at lower elevations is somewhat in question, the jet
dynamics/modest lift are hard to ignore and should aid in precip
development even outside of the mountains. In addition, a potent s/w
is forecast to move through the area over the weekend, pushing a
strong Pacific cold front through. The front should be accompanied
by at least some shower activity for valleys/plains and may lead to
a period of gusty winds areawide as it moves through. In addition,
after a brief moderating trend this week, this front should usher in
colder air once again by early next week. Of note, the EC/GFS differ
on the timing of the front, but agree on the general idea of the
front moving through. The CMC is much slower with the associated s/w
and brings a strong SFC low through the heart of the CWA. Again,
leaned away from the CMC for now due to a lack of support from
other models. Martin

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  22  16  28  17 /  20  10  30  10
CTB  18   7  23  15 /  20  10  30  10
HLN  24  15  27  15 /  30  20  30  10
BZN  25  16  27  11 /  20  20  30  20
WEY  21   7  19   3 /  50  50  50  30
DLN  25  13  26  13 /  20  30  30  10
HVR  22  12  27  15 /  20  20  20  10
LWT  20  12  28  14 /  10  10  30  20

&&

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

&&

$$

weather.gov/greatfalls



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