Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 222352
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
452 PM MST Wed Nov 22 2017

Aviation Section Updated

.SYNOPSIS...

A brisk westerly flow aloft will reside over the region through
Thursday. As a result, expect periods of strong winds over the
region, especially on Thursday. Additionally, periods of rain are
expected over the western mountains. The rain will gradually change
to snow on Thursday night, as a Pacific cool front moves through the
region. Looking ahead to the weekend, it will be mild through early
Sunday, along with windy conditions. There will be a chance for rain
and snow showers by late Sunday afternoon.

&&

.DISCUSSION...

Tonight through Friday...A unique weather pattern will make for an
interesting Thanksgiving Holiday filled with wind, rain, near
record temperatures, and possible localized flooding concerns.
Starting with the winds, flattening ridge will start to increase
winds across the region this evening. Ahead of an approaching cold
front, the pressure gradient only increases, causing strong winds
to develop overnight, especially across northwest portions. Here
a High Wind warning is now in affect tonight through Thursday
evening. As a cold front and clipper system push across the
CWA, 50 to 80 knots of wind at 700 mb may mix down through the
day on Thanksgiving and continuing into the evening hours. Thus a
wide area of strong winds are possible, and have continued a High
Wind Watch for most of the CWA. Winds then diminish below High
Wind criteria from west to east Thursday night.

Little precipitation is expected tonight through Thursday
morning, except across the favored mountains in upslope flow. At
these favored areas expect to see snow level fairly high and above
8000 feet. The mentioned cold front then pushes through Thursday
afternoon and evening bringing mainly rain showers. PWAT values
on this morning`s sounding are fairly high for this time of year,
and will remain high through tomorrow. Some areas may see
moderate to high amounts of liquid QPF...and mostly in rain form.
The areas that look to get hit the hardest are along the Rocky
Mountain Front, central, and southern Montana. Concerns with a lot
of rain over a decent snow pack may elevate localized flooding
potential, especially along the Rocky Mountain Front. See the
Hydro section for more details. This front then stalls across the
south Thursday night into Friday morning, lingering precip
chances. Enough cold air may also lower snow levels to around 4000
or 5000 feet during this time period. Light snow accumulations
will be possible for the southwest portions on Friday morning.
Precip chances then diminish Friday afternoon. And to top off this
unique holiday forecast, high temperatures look to be near record
readings for Thanksgiving in the 60s. Friday will be slightly
cooler and see more near normal values behind the cold front.
Anglin

Friday night through Wednesday...Medium range models are in fairly
good agreement in the depiction of an active but relatively
mild/progressive weather pattern through the middle of next week.
Period begins with an upper level ridge progressing east across the
western U.S. this weekend. Temperatures will warm to nearly 20
degrees above seasonal averages Sat/Sun. Breezy west winds across
the plains on Saturday will increase on Sunday as weak shortwave
moves up and over the ridge through southern Alberta, sending a weak
and mostly dry surface trough/front across the region Sunday
afternoon/evening. A larger scale upper level trough then moves
onshore Sunday night and progresses east across the Northern Rockies
and MT Monday/Mon night. This will send a cold front across the
region Monday with cooling temperatures and lowering snow levels
though Monday night. Models are still somewhat ambiguous with
smaller scale shortwave details within the trough, but a period of
precipitation appears likely for most areas with the passage of this
system, though its quick movement will likely limit precipitation
amounts to the lighter side for most areas with models trending
towards central and southwest MT as the most likely location for the
development of band of frontal precipitation which could involve
rain changing to snow for lower elevations. Upper level ridge builds
back in behind this system on Tuesday and Wednesday for drier
conditions. Hoenisch


&&

.AVIATION...
Updated 2352Z.

VFR conditions expected through the current TAF cycle, but
breezy/windy conditions will impact all terminals, especially
Thanksgiving afternoon.

Moisture continues to stream into the area from off the Pacific at
this time, but downsloping continues to keep precip mainly confined
to the mountains (where lower clouds and mtn obscurations are
occurring). This will continue to be the case overnight. On Thursday,
a cold front will begin to approach the area, but lower
clouds/precip over the plains/valleys should hold off until just
beyond the current TAF cycle. It will be breezy/windy at times ahead
of the front, first across Central MT and KEKS, then areawide
Thanksgiving afternoon. MARTIN

&&

.HYDROLOGY...
Updated 3 PM.

Periods of rain are expected to continue over the northern Rockies
tonight through Thursday. Rainfall amounts of 1 to 2 inches are
possible. This amount of rainfall, combined with melting snow, could
lead to some minor flooding problems on creeks/streams that flow out
of the mountains. Flood highlights are possible on Thursday should
impacts develop. On Thursday night, cooler air moves into the
region, changing the rain to snow and diminishing the threat for
flooding. Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  51  65  37  47 /  10  10  50   0
CTB  45  60  36  45 /  10  30  50  10
HLN  41  60  34  44 /  10  10  60  10
BZN  41  59  31  44 /  20  10  70  20
WEY  36  44  28  39 /  20  20  60  30
DLN  41  61  31  44 /  20  10  50  10
HVR  48  65  36  50 /  10  10  30  10
LWT  48  64  34  45 /  10  10  30   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from 11 PM this evening to 11 PM MST Thursday
Eastern Glacier...Eastern Pondera...Eastern Teton...Liberty...
Northern Rocky Mountain Front...Southern Rocky Mountain Front...
Toole.

High Wind Watch from Thursday afternoon through late Thursday
night Beaverhead...Broadwater...Gallatin...Jefferson...Madison...
Meagher.

High Wind Watch from late tonight through late Thursday night
Blaine...Cascade...Central and Southern Lewis and Clark...
Chouteau...Fergus...Hill...Judith Basin.

&&

$$

http://www.weather.gov/greatfalls



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