Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 280501

Area Forecast Discussion
National Weather Service Great Falls MT
1000 PM MST Mon Feb 27 2017



Increased PoPs/QPF and snow amounts for Tuesday into Tuesday
night especially over the northern Plains as an upper disturbance
interacts with a weather front to generate at least some brief
areas of light snow. Snowfall over the SW MT mountainous region
looks to fall as generally diurnally convective snow showers.



A broad area of low pressure over the area will continue at least
mountain top-obscuring snow in the mountains. Otherwise, VFR
conditions with mainly mid level cloudiness and a few snow showers
are expected to continue at the terminals through the next 24 hours.
Some heavier showers could cause brief periods of MVFR conditions,
especially with the passage of a disturbance after 12Z. A frontal
boundary will also move east of the area with the disturbance after
18Z, shifting winds more westerly across the area.


/ISSUED 455 PM MST Mon Feb 27 2017/
Tonight through Wednesday...Two upper level disturbances will move
through the region over the next few days. Once disturbance will
move through this evening...while the second disturbance will
move through during the day on Tuesday. Each disturbance will
produce scattered snow showers...generally up to an inch of
snowfall is possible with each disturbance...slightly more in the
mountains. On Wednesday...another trof will move through the
northern portions of the region. Expect gusty west winds to
develop with this trof on Wednesday...with wind speeds just below
warning criteria along the front range. Some blowing snow is
possible on Wednesday...mainly west of I-15. Temperatures will
continue to be below normal through the period...but a
slow/gradual warming trend is expected from Tuesday into
Wednesday. Brusda

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


GTF  14  31  17  37 /  20  20  20  30
CTB   5  24  16  33 /  30  50  20  20
HLN  16  31  17  36 /  20  20  20  20
BZN  13  31  10  33 /  30  30  20  30
WEY   6  21   0  23 /  50  60  40  50
DLN  13  28   7  33 /  30  30  20  10
HVR   8  26  10  35 /  20  30  30  40
LWT  12  30  13  33 /  10  30  30  40



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