Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 141733
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1033 AM MST Thu Dec 14 2017

UPDATED AVIATION

.816 AM MST UPDATE...

As the sun rises, webcams have revealed the presence of freezing
fog in the valleys of Beaverhead County. Thus, added this county
to the freezing fog advisory in effect until 11 AM this morning.

.733 AM MST UPDATE...

Most of today`s forecast remains valid. However, freshened
temperature grids in the Bozeman area per latest observations and
model data. Also decided to extend the freezing fog advisory for
parts of Southwest MT until 11 AM this morning. Believe the fog
will persist longer than originally forecast.
Jaszka

&&

.SYNOPSIS...

High pressure building aloft will provide mostly sunny skies for
the area today. However, dense fog may be slow to clear out of
southwest valleys. West winds strengthen early Friday across
North-central Montana. A cold front arrives Friday night with
chances for accumulating snow.

&&

.AVIATION...
Updated 1733Z.

Mainly VFR are forecast for the next 24-hours. Expect northerly to
northwesterly flow aloft and passing upper-level clouds. Patchy
freezing fog and associated CIGS/VSBY down to LIFR should dissipate
by 20Z/Thur in SW MT valleys. Westerly surface winds strengthen
along and near the Rocky Mountain Front, including KCTB, by late
this evening. Mountain wave activity will also increase as a Pacific
disturbance begins its approach.
Jaszka

&&

..PREV DISCUSSION...
/ISSUED 440 AM MST Thu Dec 14 2017/

Today through Saturday...Dense freezing fog developed overnight in
southwest valleys with clearing skies over a fresh snowfall. A
freezing fog advisory is in effect through 8am. This may need to
be monitored and possibly extended later into the morning for some
areas. Impacts include low visibility and continued icy road
surface. Allow extra time and travel with caution this morning.
Otherwise expect mostly sunny skies today with some high clouds
slipping over the strengthening ridge to our west. Low level warm
advection and subsidence aloft will restore valley temperature
inversions through Friday. The western ridge collapses rapidly on
Friday as a strong weather system moves through the PacNW.
Westerly downslope winds will strengthen Friday morning along the
Rocky Mountain Front. At this time, model profiles do not support
adequate mixing to bring warning criteria winds to the surface.
Nonetheless, those working outdoors or driving lightweight high-
profile vehicles through this area should exercise caution. A cold
front arrives later Friday night, producing widespread
precipitation across the area through mid-day Saturday. Depending
on time of arrival, precipitation could begin as rain at lower
elevations before switching to snow at all elevations overnight.
Snow totals through Saturday range from around an inch at lower
elevations to near 6 inches in the mountains. Anyone traveling
over mountain passes will need to slow down and allow extra time
to reach their destination. Snow moves out of the region Saturday
night, with clearing skies enabling chilly overnight temperatures
closer to mid- December averages.
PN

Saturday night through Thursday...An unsettled weather pattern will
reside over the region, with a gradual shift towards colder
temperatures over North Central MT by late in the period. Breezy
west winds develop on Sunday allowing the I-15 corridor to warm up a
bit from Great Falls to Cut Bank, otherwise expect another round of
light snow to move through the region late Sunday night through
Monday. A few snow showers linger into Tuesday, otherwise the next
major weather system will be the cold front pushing southward from
Canada into Montana either on Wednesday or Thursday. Models have
differed quite a bit on the day in which the cold air moves south.
Additionally, the track of the main low pressure system does not
favor heavy snow over North Central MT, but a period of accumulating
snow is possible over Central/Southwest MT. For afternoon
temperatures over North Central MT through much of the week, I went
a touch below the blend solution, with Thursday being about 5
degrees below the blends. I did not go quite as cold as the raw
GFS/MEX numbers are progging at this time though. Overall near
normal temperatures are expected in the Southwest through much
of the period.
Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  43  33  48  26 /   0   0  20  70
CTB  45  31  44  23 /   0   0  40  80
HLN  29  19  37  24 /   0   0  10  50
BZN  29  13  35  21 /   0   0   0  60
WEY  25   5  24  14 /   0   0  10  60
DLN  30  16  36  21 /   0   0   0  40
HVR  41  27  47  26 /   0   0  30  70
LWT  42  28  50  25 /   0   0  10  50

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Freezing Fog Advisory until 11 AM MST this morning Beaverhead...
Broadwater...Central and Southern Lewis and Clark...Gallatin...
Jefferson...Madison.

&&

$$

http://www.weather.gov/greatfalls


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