Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 231800
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1100 AM MST Fri Feb 23 2018

.UPDATE...

...11am MST Update...
Issued a Winter Weather Advisory for Toole, Liberty, Hill, Eastern
Pondera, Eastern Teton, Chouteau, Cascade, and Judith Basin
Counties until 6am MST on Saturday. Winds gusting to near 40 mph
already are causing areas of blowing and drifting snow across the
aforementioned counties. In addition, spotters are reporting
reduced visibilities due to the blowing snow on major US Highways.
- Moldan


...930AM MST Update...
Morning update has been published, with
only minor adjustments made to winds and temperatures for today.
Lowered high temperatures across the Southwest Montana Valley`s
and in the Milk River Valley across North Central Montana for
today, as limited mixing and the depth of the cold/Arctic air in
place should be stubborn to moderate in these areas today. In
addition, increased winds slightly further along the Rocky
Mountain Front and across the plains of North Central Montana to
account for current observed values and latest guidance from the
12z WRF models. Blowing and drifting snow has already been noted
along the Rocky Mountain Front this morning via webcams, with some
roads already becoming closed (ie United States Highway 89 from
Two Medicine Creek to Browning) or reporting severe driving
conditions. Expect conditions to deteriorate further along the
Rocky Mountain Front and into Eastern Glacier County today as wind
speeds increase further. Given high temperatures across this
region won`t exceed freezing, am not worried about the snow
crusting over and not being able to be blown around. The one
limiting factor to how much snow blows around today is how much
has already be scoured out/compacted from recent wind events,
which unfortunately is unknown from this distance here in Great
Falls. - Moldan

&&

.SYNOPSIS...

Windy conditions are expected Friday, and again on Sunday, which
will lead to impacts from blowing and drifting snow. Along the
Rocky Mountain Front, ground blizzard conditions are expected
today through early Saturday morning. Periods of snow are expected
over the mountains but lower elevations should remain mostly dry.

&&

.AVIATION...
Updated 1140Z.

Areas of light snow will continue to produce IFR/MVFR conditions
across portions of southwest Montana through 15Z with improving
conditons thereafter. Remainder of the forecast area is expected to
see primarily VFR conditions with areas IFR/MVFR due to freezing fog
through about 18Z. Strong and gusty southwest to westerly winds
develop along the Rocky Mountain Front this morning then spread out
over the plains through the day. Widespread blowing and drifting
snow is expected along the front range of the Rockies producing
areas IFR/MVFR visibilities through the forecast period. Patchy
blowing snow is expected over the plains. mpj

&&

.PREV DISCUSSION...
/ISSUED 935 AM MST Fri Feb 23 2018/
FXUS65 KTFX 231635
AFDTFX

Today through Sunday...Montana will remain remain under the
influence of upper level troughing through the short term forecast
period. A disturbance moving through the upper trough will
continue to bring light snow to portions of southwest Montana this
morning with only minor accumulations expected. Periods of snow
can also be expected over the mountains of the Continental
Divide at times through the short term but the plains are expected
to remain mostly dry. Biggest concern for the short term
continues to be strong and gusty winds causing blowing and
drifting snow today through early Saturday morning, especially
along the Rocky Mountain Front. Have kept the Blizzard Warning for
this area intact with no major changes in the forecast
anticipated. Another round of windy weather can be expected on
Sunday with winds possibly exceeding high wind criteria over a
large portion of north central and central Montana. Have kept the
Winter Storm Watch in effect for now, but the Sunday event will
also feature warmer temperatures for much of the region. This
raises the possibility that blowing snow may not become as
widespread as anticipated if temperatures are sufficiently high to
cause the existing snowpack to crust over. mpj

Sunday Night through Friday...A broad low pressure trough will
remain over North America through this period, but some differences
develop among the models beginning on Wednesday. A progressive
weather pattern with a mostly westerly flow aloft with weak embedded
disturbances will persist through Tuesday night. The strong westerly
winds will decrease overnight Sunday night and into Monday as a
shortwave trough swings southeast through the Pacific Northwest and
into the Great Basin. This will keep the best chance for snow in the
mountains of western and southwest Montana with decreasing blowing
snow. This shortwave will then split Monday night and Tuesday,
sending the strongest energy south toward the western U.S./Mexico
border through Wednesday and leaving only a chance of mountain snow
for the forecast area. As mentioned above, this is where the
divergence in forecast solutions develops. The ECMWF and Canadian
models dig a deep upper level low pressure area south along the
Canadian and U.S. Pacific coasts for Thursday through Friday. This
would bring an increasingly moist southwest flow to the forecast
area, as well as an increasing chance of snow over the entire
forecast area, especially for Friday. The GFS model maintains more
of a westerly flow aloft through the latter part of the work week,
which would keep the better chance for snow over the mountains, as
westerly downslope winds keep the plains mostly dry. Will therefore
go with a chance of snow near climatological normals for this period
and make adjustments as models progress over the next few days.
Model consensus temperatures do not vary much through this period,
keeping highs mostly 10 to 15 degrees below normal (in the 20s) and
lows 5 to 10 degrees below normal (in the single digits to lower
teens).  Coulston

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  25  16  29  11 /   0   0  20  20
CTB  24  14  28  10 /   0   0  20  10
HLN  23   6  30   9 /   0  10  40  30
BZN  19   3  26   6 /   0  10  30  50
WEY  18  -2  17  -3 /  30  60  70  60
DLN  17   7  22   4 /  30  20  50  30
HVR  13  10  23   5 /   0   0  10  10
LWT  24  11  27  11 /   0   0  20  40

&&

.TFX WATCHES/WARNINGS/ADVISORIES...

Winter Weather Advisory until 6 AM MST Saturday Cascade...
Chouteau...Eastern Pondera...Eastern Teton...Hill...Judith
Basin...Liberty...Toole.

Winter Storm Watch from Sunday morning through Sunday evening
Blaine...Cascade...Chouteau...Eastern Pondera...Eastern Teton...
Fergus...Hill...Judith Basin...Liberty...Toole.

Blizzard Warning until 6 AM MST Saturday Eastern Glacier...
Northern Rocky Mountain Front...Southern Rocky Mountain Front.

&&

$$

http://www.weather.gov/greatfalls



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