Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 111713
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1013 AM MST Wed Jan 11 2017

UPDATED AVIATION

.501 AM MST UPDATE...

Dropped remaining Winter Weather Advisories across portions of
southern Lewis and Clark...Judith Basin...and Fergus counties...as
snow has either ended or will end shortly. Extended timing of
Advisories for Broadwater and Jefferson Counties for lingering
light snow causing impacts to those on their morning commute. The
Winter Weather Advisories across the south remains the same as
previous publish. Wind Chill Advisories remain for much of
northern Montana for this morning.

In addition...updated aviation discussion.

&&

.DISCUSSION...

Today through Friday...IR imagery showing nicely the two weather
scenarios across the CWA this morning. in the central and we the
Canadian front stalling...with light to portions of moderate snow
along and ahead of this front. Behind the front...and showing up
quite nicely...clouds have cleared and very cold air is filtering
into the region. Lows in the -20s will easily be found. How far
will the very cold air push is still up for debate. Just enough
low clouds are hindering very cold temps from about Great Falls to
Lewistown. Current thinking is these clouds will briefly
diminish...bringing the cold air to about this line. Some light
breezes are also being found behind this front...thus issued a
Wind Chill Advisory until noon for much of the northern portions.
Cascade county was left out...due to uncertainty of the cold
air...and lighter winds. Hill and Blaine county will need to be
monitored as increasing winds today could bring dangerous wind
chills well past noon. Meanwhile across the south...the mentioned
stalled front will bring periods of snow through today and this
evening. Light snow may even persist into tonight. Extended the
advisory until 12z Thursday to account for some lingering
snow...and perhaps some blowing snow. Mainly dry conditions are
expected elsewhere...although there is a slight chance for
flurries or brief light snow across the Hi-Line this evening.
Confidence is low so left it as just 10 percent chance for now.
Flurries and scattered light snow may still be found across the
south Thursday morning...then diminish Thursday afternoon. Dry
condtions are expected elsewhere. Much of the CWA will find itself
sandwiched in between a cut off low in the Great Basin area and
a clipper system in the Northern Plains. This results in
increased dry westerly flow. Gusty winds are possible
Thursday...and will need to be monitored for possible blowing and
drifting snow advisories. A similar set up will be found on
Friday...dry conditons across the CWA...with breezy winds at
times. More blowing and drifting snow will be possible...and again
will need to be monitored. Temperatures will be well below normal
today with the arctic like air and fresh snow. With the mentioned
breezy winds on Thursday and Friday...we will start an extended
warming trend...with highs in the 20s by Friday. Overnight lows
will once again be bitterly cold tonight into Thursday...and will
have to monitor for more Wind Chill products...especially across
the north. Anglin

Friday night through Wednesday...While we may not completely lose
the active weather pattern of late, it does appear that we are
headed into a pattern that will favor moderating temperatures and
somewhat drier conditions. This also appears to be a favorable
pattern for breezy/windy conditions at times, especially across
central Montana.

The period starts with somewhat of a split-flow pattern aloft with a
slow-moving upper level low moving through the Four Corners region
and ridging developing from the northern Rockies into southern
Canada. In general, this will likely lead to mostly dry conditions
through Sunday.

As the upper low ejects into the central US next week, the models
begin to diverge on how the pattern will evolve across the western
US. Initially, a brief zonal flow is likely, potentially followed by
more of a SW flow aloft as ridging develops across parts of the
western US. The key is where will the ridge axis setup as this has
significant implications on temps, precip, winds. For now, thinking
the moderating temperatures and drier conditions will continue on
into at least Monday. Interestingly, by Tuesday/Wednesday, the
models suggest another atmospheric river event may impact parts of
the western US, although the trajectory of this one may be aimed a
bit more north compared to the most recent one which would favor
higher precip along/west of the Continental Divide. Locally, then,
this would likely bring widespread precip back to the mountains,
but downsloping may tend to limit precip somewhat across the
plains/valleys. Still, if this were to pan out, I would have to
believe at least some precip would be able to reach the
plains/valleys given the potential for anomalous moisture content.
Something to keep an eye on for next week.

Regardless of precip, the models are very consistent in moderating
temperatures through next week. In fact, some guidance suggests a
good likelihood of seeing highs at least as mild as the 40-45+
degree range for parts of central Montana with highs near/above
freezing across the SW valleys. But, again, the placement of the
ridge may be key in just how mild it can get next week.

Lastly, the models have been very consistent over the past couple of
days regarding periods of breezy/windy conditions across central
Montana late in the weekend and into next week. While that hasn`t
completely changed, the wind potential doesn`t look quite as
impressive with this morning`s runs as the last couple of days, but
still worth watching as the potential for high winds still remains
very much possible. Martin

&&

.AVIATION...
Updated 1713Z.

Low pressure trough aloft will maintain westerly to northwesterly
mid- to upper-level flow through 18Z/Thu. Predominantly VFR expected
in North-Central MT and at KHLN throughout TAF period. Disturbances
moving through the aforementioned trough will likely allow mainly
light snow to persist at KBZN/KEKS through most of the period.
Mainly MVFR CIGS/VSBY expected in this snow over Southwest MT, but
worse conditions are possible at times. Expect mountain obscuration,
especially in Southwest MT.
Jaszka

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF   7  -8  18  10 /  10  10   0   0
CTB  12 -10  14   4 /  10  10  10   0
HLN   7  -9  17   1 /  30  10  10   0
BZN   9  -5  20  -2 /  50  30  20  10
WEY  24   2  19 -12 /  90  70  30  10
DLN  15   3  21  -1 /  60  30  20   0
HVR   2 -13   6  -7 /  10  10  10   0
LWT   6  -6  18   8 /  20  10   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 11 AM MST this morning
Broadwater...Jefferson.

Wind Chill Advisory until noon MST today Blaine...Chouteau...
Eastern Glacier...Eastern Pondera...Eastern Teton...Fergus...
Hill...Judith Basin...Liberty...Northern Rocky Mountain Front...
Southern Rocky Mountain Front...Toole.

Winter Weather Advisory until 5 AM MST Thursday Beaverhead...
Gallatin...Madison.

&&

$$

weather.gov/greatfalls



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