Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 170557
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1057 PM MST Thu Feb 16 2017

AVIATION SECTION UPDATED

.UPDATE...

Main update this evening is to add scattered showers (and
possibly a few thunderstorms) from Central Montana into the
eastern TFX zones. Convective showers have developed this evening
along a passing Pacific cold front from near Butte northeast to
Fort Benton, including the Helena and Great Falls areas, where
wind gusts in excess of 45 mph occurred. This main band of showers
will continue to weaken as it moves east/spreads northeast into
the Lewistown and Havre areas overnight. The main threat for
thunderstorms will likely only linger until midnight or so as the
marginally unstable airmass continues to stabilize. The main
threats from any storms will be brief heavy rain and strong wind
gusts.

Have also increased the mention of snow showers along the
Montana/Idaho border to better reflect current conditions, as West
Yellowstone has occasionally fallen below one mile visibility in
snow this evening. Models indicate that the snow there should
decrease after midnight as well.

Otherwise, breezy winds should keep overnight lows fairly mild,
which are trended well in the current forecast.
Coulston

&&

.AVIATION...
Updated 0557Z.

A Pacific cold front has pushed through the forecast area, but
lingering moisture/lift in the wake of the front is keeping
SHRA/SHSN going, mainly impacting areas near KGTF/KLWT/KHLN/KBZN.
Any shower that moves through will have the potential to cause a
brief period of gusty winds in excess of 30kt (similar to what was
seen at KHLN/KGTF/KBZN recently). Showers should diminish over the
next several hours. Across central MT, the wind may decrease some
overnight, followed by a period of gusty winds Friday afternoon.
SCT/BKN low/mid level clouds and areas of mtn obscurations should
begin to decrease Friday afternoon as a drier/westerly flow aloft
develops. Late in the period, the next surge of moisture may begin
to bring increasing clouds to far SW MT, possibly impacting
KEKS/KBZN, but for now am not expecting any precip at those sites
later Friday. Martin

&&

.PREV DISCUSSION...
/ISSUED 506 PM MST Thu Feb 16 2017/

Tonight through Saturday...The upper level ridge that has brought
record breaking warmth to much of the forecast area will move
east of the forecast area tonight. Behind the ridge, a short wave
disturbance will sweep across Montana tonight and Friday bringing
snow to the mountains along the Continental Divide and a slight
chance to chance for rain, snow or possibly freezing rain to lower
elevations of the CWA. Windy conditions will continue along the
Rocky Mountain Front and over the adjacent plains, but wind speeds
will likely be less than those seen today. High temperatures will
be about 5 to 10 degrees cooler on Friday as well. The disturbance
pushes eastward Friday night with a weak shortwave ridge building
over the region for relatively dry conditions and much lighter
winds. As the progressive pattern aloft continues on Saturday the
flow aloft becomes moist and southwesterly with a few weak
disturbance bringing a chance to low likelihood for additional
precipitation over the mountains and in southwest Montana. Cloudy
skies and developing east-southeast winds will also allow
temperatures to cool another few degrees for Saturday highs. mpj

Saturday night through Thursday... A southwesterly flow aloft will
prevail over the region on Saturday night, as the next upper level
trof moves through the region Sunday and Sunday night. Expect a
chance for rain/snow showers as the trof moves through. Snow
amounts mainly of an inch or two are possible in the mountains...
but in the mountains of far Southwest MT near the MT/ID border...
2 to 4 inches will be possible. A short break in the precipitation
is possible for a time Monday, before the next area of low
pressure moves through the region on Tuesday. This system has
weakened compared to prior solutions, but will maintain a chance
for mixed rain and snow Tuesday night. Temperatures trend
downward, closer to seasonal averages for Wednesday. A stronger
longwave trough is forecast to develop over the western U.S. on
Thursday. This will bring temperatures down to near or just below
seasonal average with chances for snow at all elevations. The
higher snow accumulations for this scenario would occur over
southwest Montana as the surface and 700 hPa low centers pass to
the south of our forecast area. PN

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  38  54  30  51 /  60  10   0  10
CTB  34  47  24  41 /  10  10   0  20
HLN  32  44  20  41 /  70  10  10  20
BZN  29  43  21  43 /  30  10  10  20
WEY  23  35  19  36 /  70  20  50  60
DLN  27  43  26  44 /  30  10  20  30
HVR  40  53  28  48 /  20  10   0  10
LWT  37  53  29  52 /  30  20   0  10

&&

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

$$

weather.gov/greatfalls



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