Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 201112

Area Forecast Discussion
National Weather Service Great Falls MT
412 AM MST Tue Feb 20 2018

...Update to Aviation...


After a very cold morning for all locations across the area,
expect sunshine to return in full-force this afternoon. We remain
in a rather calm, yet cold weather pattern for the next several
days with light snow chances, primarily across south-central and
southwestern areas. The next system will arrive by later this
upcoming weekend with more widespread snow chances possible.



Tonight through Wednesday...With the previous stretch of very
active winter weather now behind us, we begin to transition into
more of a tranquil weather pattern for the next few days. Looking
aloft, we remain in control of dominant broad west-coast trough
yielding persistent low height anomalies. At the surface, a weak
area of high pressure across east-central MT will continue to
press eastward which will help keep winds primarily from the
southwest today. With very cold air in place, wind chills will
easily persist well below -20F for some, mostly across northern
and north-central MT through the morning hours where a Wind Chill
Advisory remains in effect. Afternoon highs will likely rise into
the teens across the Plains, while the valleys to the SW remain
locked in the colder air and will struggle to rise above the
single digits with mostly sunny skies across the area. By tonight,
the next weak shortwave is expected to arrive from the northwest,
along the counter- clockwise flow dominated by the aforementioned
west-coast trough. This will help with increasing cloud cover
from NW to SE throughout the night tonight given increasing
PVA/dynamic upper- level support. By Wednesday, the trough swings
through the area and may support enough lift to squeeze out some
light snow showers across south- central and southwestern MT. A
more thorough investigation of the northward extent of the light
snow potential illustrates very little, if any, support for snow
chances from LWT to GTF northward. However, decided to keep the
mention of at least a slight chance of snow Wednesday morning up
to GTF with mainly dry conditions expected to the north. Afternoon
highs on Wednesday will range only a few degrees warmer, but will
still be well below-average area-wide. KLG

Thursday through Monday...The next, stronger shortwave trough is
expected to follow the departing system on Wednesday across
coastal British Columbia. This trough will eventually press south
across the Pac NW and close off as an upper-level low. With our
area downstream of this system, expect increasing cloud cover with
more light snow chances, primarily across SW areas during the day
on Thursday. By Friday, this system will swing across the central
Rockies to our south, with a stretched area of upstream vorticity
and weak troughing to follow across our area. Regardless of
notable upper-level dynamic support in place, moisture will
remain rather starved, as PW`s range close to daily minimum values
per sounding climatology (~0.08" to 0.10"). With that said, going
to continue limiting any northward extent of snow potential and
keep chances primarily to south-central and southwestern MT,
specifically localized to any enhancement caused by terrain.

Once this trough passes, we return to a zonal pattern beginning on
Saturday. However, as this transition progresses, heights will
tightly pack across the area which will lead to increasing winds
aloft. H700 winds between 40 to 50kts will increase beginning in
the morning hours on Saturday, lasting throughout the day where
afternoon mixing will aid in downward transport, leading to breezy
or windy conditions. ATTM, not expecting this to cause any major
impacts, as winds aloft are not supportive for excessive windy
conditions. Like clockwork, the next shortwave trough arrives
across the Pac NW on Sunday which will drive Pacific moisture
across the area in the form of increasing cloud cover. This will
be followed by increasing snow chances along the Divide,
eventually spreading out into the Plains. Most long-range model
guidance is lacking much in the way of moisture supportive for any
significant accumulations like we`ve been seeing with previous
systems. However, confidence of lighter snow and associated
accumulations looks good, and will continue to monitor this system
in the upcoming days. KLG


Updated 1112z

Patchy areas of low clouds continue across BZN and EKS early this
morning, which has brought intermittent periods of MVFR to IFR
conditions, especially across EKS. Expect CIGs in and around 020 to
060 through daybreak, with variations in flight categories possible.
Low clouds/fog has started to work into HVR at this hour, which is
also leading to MVFR conditions. For all mentioned terminals, expect
conditions to slowly improve during the morning hours back to VFR
and lasting through the rest of the day. Otherwise, all other
terminals are clear and expected to remain that way through the
forecast period. KLG


GTF  13 -12  17  -8 /  10  10  20   0
CTB  15 -15  15  -7 /  10  20  10   0
HLN  13  -7  19  -4 /  10  10  20  10
BZN  10  -8  17  -5 /  10  10  20  10
WEY   8 -16  13 -11 /  20  30  30  30
DLN  12  -8  14  -4 /  10  10  20  20
HVR   8 -16   8 -15 /  10  10  10   0
LWT  11 -11  17  -6 /  10  10  10   0


Wind Chill Advisory until noon MST today Blaine...Cascade...
Chouteau...Eastern Glacier...Eastern Pondera...Eastern Teton...

Wind Chill Advisory until noon MST today Fergus...Judith Basin...

Wind Chill Advisory until noon MST today Central and Southern
Lewis and Clark...Northern Rocky Mountain Front...Southern Rocky
Mountain Front.


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