Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 071753
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1053 AM MST Wed Dec 7 2016

.DISCUSSION...

Although bitter cold temperatures will continue across the area
throughout the day, winds have generally dropped below 10 mph from
the Rocky Mountain Front south into Southwest Montana, so have
dropped the Wind Chill Advisory there. However, winds of 10 to 15
mph will gust to between 20 and 30 mph at times along and east of
a line from Cut Bank to Stanford through this evening. This will
be especially true between the Highwood and Little Belt Mountains
in Judith Basin County and off the Bears Paw Mountains in central
Blaine County. Have therefore extended the Wind Chill Advisory for
these areas until 10 pm this evening. Am anticipating winds to
drop below 10 mph at that point. Temperatures tonight will likely
be the coldest that they have been across the region in at least a
year, with widespread lows of 10 to 15 below zero, but the
relative lack of wind overnight should keep wind chills from
reaching bitter cold levels.  Coulston

&&

.AVIATION...Updated 1750Z.

VFR conditions will generally continue across the region today,
but patchy freezing fog will reduce visibility to MVFR levels at
times along the Rocky Mountain Front and into the Southwest
Montana valleys. Breezy northwest winds will also persist into
this evening across the plains of North Central Montana. High
pressure aloft will begin to build into the area from the
Southwest overnight, which will help clear out the area and cause
winds to decrease. There will continue to be a threat for patchy
freezing fog in the southwest valleys overnight, but conditions
will likely not fall below MVFR.  Coulston

&&

.PREV DISCUSSION...
/ISSUED 425 AM MST Wed Dec 7 2016/

Today through Friday...Northwesterly mid- to upper-level flow and
the arctic surface high pressure ridge should continue to persist
over the CWA through Thursday morning. A shortwave trough embedded
within the flow aloft will move southeastward during the course of
the day today. Lift and limited moisture ahead of this disturbance
should result in nothing more than scattered snow flurries and a
dusting of snow accumulation across the region. By Thursday
afternoon, still expect diffluent southwesterly flow aloft and
associated lift ahead of a low- to midlevel shortwave trough
approaching from the Pac NW to allow surface pressure falls to
commence over the CWA. In addition, model data are now in better
agreement that a surface warm front accompanying the disturbance
will advance northward into Southwest MT and near the I-90
corridor by Thursday evening. This pattern looks favorable for
isentropic lift of the aforementioned southwesterly flow of warm,
moist air to occur over the arctic air mass remaining over most of
the area, ahead of the front. The pattern will set the stage for a
widespread snowfall, especially Thursday night into early Friday
morning.

By daybreak Friday, snow looks to become more scattered over the CWA
as the aforementioned disturbance weakens while moving farther
eastward and flow aloft becomes more zonal due to a rather flat
mid- to upper-level high pressure ridge building-in from the Pac
NW. This shift in the flow aloft will cause isentropic lift to end
over our area. Thus, during the day on Friday, upslope flow looks
to become the main trigger for snow. On Friday, the aforementioned
warm front looks to move farther north toward the Central MT
mountains. With southerly surface flow south of the front and
easterly to northeasterly flow ahead of it, places such as the
south aspects of Southwest MT mountains and the north/east
aspects of the Rocky Mountain Front, Little Belts, and Big Snowy
Mountains will likely experience upslope snow showers. Winter
weather highlights may be needed for at least a portion of the CWA
for Thursday into Friday, but will wait for more model guidance
before issuing any highlights.

As for temperatures, low and high temperatures will be about 20 to
35 degrees below normal today through Thursday. Thursday morning
still looks to be the coldest for many places due to mainly clear to
partly cloudy skies. Thus, the wind chill advisory will remain in
effect for the entire CWA through at least noon today and will
likely be extended with the forecast update later this morning. By
Thursday night and Friday, the aforementioned warm front will
cause a more marked variation in temperatures. South of the front,
many places in Southwest MT will have lows in the 5 to 15 degree
range Thursday night and highs in the lower 20`s to mid 30`s for
Friday. North of the front, most places in North-Central MT will
experience lows in the range of 0 to -10 degrees Thursday night
and highs in the single digits or teens on Friday.
Jaszka

Friday Night through Tuesday...An upper level low pressure
shortwave will move over the West Coast Friday night and moisture
ahead of this system will be crossing the Rockies. A surface front
will lay across the zones with the result that the northern zones
will be very cold while the southwest zones will be closer to
normals. The shortwave will cross the Rockies early Saturday and
continue east across the zones. Brisk west winds aloft will keep
the chance of snow mainly over the higher terrain, and especially
along the Divide. The northern tier, especially the northeast
zones, will receive the least accumulation. High pressure will
build Saturday night, the air mass will dry and also begin to
trend warmer. However, the northwest flow aloft will be quite
unsettled and snow showers will remain in the forecast. A
shortwave in Alberta will move southeast Sunday towards the
Dakotas. This will will not bring much change in the chance for
precipitation but it will bring another cold front across the
Canadian border. Temperatures Sunday will again struggle to move
above zero across the Hiline and above single digits across the
central zones. Currently, the coldest air is forecast to slide
east of the zones...but a slight change in position would cause
very cold temperatures over the eastern zones.
Zelzer

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF   0 -14   0  -5 /  10  10  10  50
CTB  -3 -18  -4 -10 /  10  10  10  40
HLN   6 -10  13   6 /  10  10  10  50
BZN   8 -10  14  11 /  10  10  10  40
WEY   9 -25  14   8 /  10  10  10  50
DLN  10  -8  16  13 /  10  10  20  50
HVR   1 -13  -1  -6 /  10  10  10  30
LWT  -1 -15   3  -3 /  10  10  10  40

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Wind Chill Advisory until 10 PM MST this evening Blaine...
Chouteau...Eastern Glacier...Eastern Pondera...Fergus...Hill...
Judith Basin...Liberty...Toole.

&&

$$

weather.gov/greatfalls


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