Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 201750
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1050 AM MST Thu Nov 20 2014

UPDATED AVIATION SECTION

.DISCUSSION...
Today...A quick update was made earlier this morning to reduce the
area of the fog advisory. Low level west flow will continue to push
east and most visibilities will be unrestricted again later this
morning. Zelzer

&&

.AVIATION...
UPDATED 1750Z.
Areas of lingering patchy fog will dissipate by 20z. Mid and high
level clouds will increase through the period. Southwest to west
surface winds will increase and become gusty after 21z. The
strongest winds will occur along the Rocky Mountain Front and over
adjacent plains. VFR conditions prevail.

&&

.PREV DISCUSSION...
/ISSUED 423 AM MST Thu Nov 20 2014/

Today through Saturday...Dense freezing fog does not appear to be
quite as widespread as it was last evening but satellite imagery
continues to show fog and low clouds across much of the area. Will
therefore continue the Freezing Fog Advisory through mid-morning.
A surface low pressure trough through central Montana has
oscillated back and forth on a scale of tens of miles. This has
caused surface winds at a few locations, including Great Falls, to
shift from westerly to light and variable or easterly with
temperatures oscillating from the lower teens to the lower 20s.
This feature will shift eastward through the day bringing westerly
winds to the entire forecast area and pushing the colder air and
areas of fog into eastern portions of the state. As a result,
temperatures are expected to rebound into the mid 30s to mid 40s
for all but extreme northern Blaine and Hill Counties. Models also
continue to show that a strong surface pressure gradient will set
up along the Rocky Mountain Front causing strong and gusty winds
to develop. This gradient may weaken at times but remains
relatively intact until a surface cold front sweeps through the
region on Saturday. Have issued a High Wind Warning for the Rocky
Mountain Front through Saturday evening and models suggest that
portions of the plains may need to be added to the warning when
the front sweeps through on Saturday. For now will hold off on
issuing a watch for the plains but will continue to monitor the
models to see how things develop. In addition to strong winds,
this front will bring precipitation to the central plains on
Saturday. With freezing temperatures expected Saturday morning there
is a risk for freezing rain across eastern portions of central
Montana as well. mpj

Saturday night through Thanksgiving...Period begins with a mid
level trough moving across MT and surface low pressure tracking
east along and just north of the MT/Canadian border Saturday
night. Cold advection, favorable upper level jet dynamics and
slightly unstable/cyclonic flow aloft will keep a chance for snow
showers across Central/SW MT while moisture wrapping around the
low-mid level circulation center passing by to the north will
bring a chance of snow showers to portions of North Central MT. NW
flow aloft continues Sunday into next week with a period of drier
conditions likely late Sunday through Monday. By Tuesday, flow
aloft buckles in response to shortwave energy coming onshore,
allowing the upper level jet to lift north into the northern
Rockies for increasing chances for precipitation. This is where
models begin to diverge significantly as the ECMWF model brings in
a stronger shortwave trough from the NW, carving out a trough over
the interior west with a much colder Canadian airmass moving into
the region Wednesday and Wednesday night. However the GFS model
continues to build upper level ridging inland Wednesday and
Thursday, resulting in a shorter lived precipitation event with
warmer temperatures overall. Confidence remains low at this point
with regard to cold air intrusion next week, but initial push of
moisture/precipitation Tuesday appears more likely regardless of
model solution and have increased pops that period. Hoenisch

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  42  32  43  31 /  10  10  10  10
CTB  40  28  41  28 /  10  10  10  10
HLN  41  27  41  27 /  10  10  10  10
BZN  39  18  37  21 /  10  20  10  10
WEY  31  13  29  18 /  20  30  30  50
DLN  39  20  37  25 /  10  10  10  20
HVR  38  23  41  24 /  10  10  10  10
LWT  46  28  45  28 /  10  10  10  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING until 10 PM MST Saturday Northern Rocky
Mountain Front...Southern Rocky Mountain Front.

FREEZING FOG ADVISORY until 11 AM MST this morning Blaine...
Chouteau...Hill...Liberty.

&&

$$

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