Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 240539
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1039 PM MST Thu Nov 23 2017

...Updated Aviation Discussion...

.SYNOPSIS...
An upper level disturbance will move through the region tonight,
producing gusty winds and a chance for rain or snow showers. It
remains mild and turns mostly dry for Friday through Sunday
morning, as a brisk westerly flow aloft develops over the region.
On Sunday afternoon, an upper level disturbance will move across
Southwest MT, producing rain or snow showers and bringing in
cooler temperatures for early next week.

&&

.EVENING UPDATE...

Latest surface analysis shows a Pacific cold front stretches from
northern CA up through NW MT and on across southern Alberta as of
8pm. Based on this, the front is coming in a bit slower than
originally forecast, but overall this doesn`t significantly change
the forecast. Ahead of the front, bands of showers have been
pushing east off the mountains and out over the plains and this
trend will likely continue through the night as the front
continues to push SE, finally reaching the MT/ID border by Friday
morning. Of note, as the front moves through, low/mid level lapse
rates steepen some. This will do two things. It may actually aid
in some elevated instability, with an isolated lightning strike or
two not completely out of the question (several strikes have been
noted over western MT and southern Canada over the past few
hours). For this reason, I added a mention of thunder along the
Divide over the next few hours. Secondly, this may also allow
some of the stronger winds aloft to mix down to the surface as the
front moves through. For now, we`ll keep the current High Wind
Warnings as is, but the threat of damaging winds appears to be
trending much more isolated for the rest of the night and mainly
confined to the plains of Central MT and the SW MT mountains. Many
valley locations across SW MT may only see gusts to 40 mph or so
through the night. Still do not expect any significant impacts
with any snow that develops behind the front (lower elevations
should stay mostly rain). MARTIN

&&

.AVIATION...
Updated 0539Z.
VFR conditions with strong surface winds will continue east of the
Rockies this evening and overnight. Surface cold front moves through
the region this evening producing rain showers with areas of MVFR
conditions, mainly south of Great Falls. Mountains will be obscured
at times through early Friday morning. Expect strong low-level wind
shear in the deeper valleys up until cold frontal passage as strong
west-southwest persist just above the surface, with the potential
for swirly winds when stronger showers are able to bring those winds
to the surface, especially at KEKS. Skies expected to become partly
cloudy with widespread VFR conditions primarily after 12Z Friday.
CC

&&

.PREV DISCUSSION...
/ISSUED 445 PM MST Thu Nov 23 2017/
Tonight through Saturday...Main concerns in the short term
continue to be the strong winds. The Pacific cool front is
approaching from the west and should move eastward through the
region overnight tonight. The front should arrive in the Great
Falls area just before Midnight and then exit the eastern portions
of the region around 6 AM Friday morning. Periods of strong winds
are expected until the front passes, thus the high wind warning
will continue. Light rain will continue along the divide this
evening, and gradually spread eastward as showers overnight. The
Plains areas north of Great Falls will have the lowest chance for
rain, while areas over Southwest MT have the highest chances. Some
snow will mix in towards the end, but snow accumulations will
generally be less than an inch or so, and mostly above 6000 feet.
For Friday and Saturday, afternoon temperatures will be cooler
than today, but still a few degrees above normal for most areas.
There will be a small chance for showers Fri/Sat, but mostly over
the Rocky Mountain Front and the mountains around Big Sky/West
Yellowstone. Brusda

Saturday night through Thursday...Progressive upper level weather
pattern continues though next week, beginning with an upper level
ridge traversing the region Saturday night though early Sunday. A
lead shortwave moving over the ridge begins to break it down late
Sunday with moisture in an increasing SW flow aloft bringing some
precipitation to the western and SW MT mountains by Sunday evening.
Medium range models begin to get out of step with the arrival of
this lead energy, with the GFS bringing a more robust Pacific
frontal passage and moisture into the region as early as Sunday
afternoon while CMC and ECMWF models hold off until late Sunday
night into Monday for this with the arrival of more substantial
energy within the incoming upper level trough axis. In either case,
look for cooling to occur Monday with details on the timing of a
period of precipitation yet to be resolved. Cooling on Monday will
allow snow levels to lower below mountain passes with main impact
and focus for winter precipitation looking to occur near the
continental divide as well as the mountains of SW MT. Upper level
ridging then builds back into the Northern Rockies and MT on
Tuesday. Beyond Tuesday, models remain out of sync with regard to
individual shortwaves but are hinting at more of a NW flow pattern
vs previously advertised ridging.
Hoenisch

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  36  46  33  50 /  40   0   0   0
CTB  37  46  31  46 /  70   0   0   0
HLN  36  47  26  46 /  60   0   0   0
BZN  31  47  22  45 /  50  10   0   0
WEY  31  40  21  37 /  60  30  10  10
DLN  34  46  24  46 /  30  10   0   0
HVR  36  50  28  49 /  30   0   0   0
LWT  35  44  29  49 /  30   0   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 5 AM MST Friday Beaverhead...Blaine...
Broadwater...Cascade...Central and Southern Lewis and Clark...
Chouteau...Fergus...Gallatin...Hill...Jefferson...Judith Basin...
Madison...Meagher.

High Wind Warning until 11 PM MST this evening Eastern Glacier...
Eastern Pondera...Eastern Teton...Liberty...Northern Rocky
Mountain Front...Southern Rocky Mountain Front...Toole.

&&

$$

http://www.weather.gov/greatfalls


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