Weather Service Report


418 
FXUS65 KTFX 240548
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1048 PM MST Fri Feb 23 2018

...Update to Aviation...

.UPDATE...
Updated forecast is out. Blizzard conditions continue along the
front range of the Rockies out to the Cut Bank area. Deep Creek
Raws had a wind gust to 92 mph this evening and Babb reported a
wind gust to 82 mph. Winds have increased further east into Judith
Basin, Fergus and Hill counties, thus the winter weather advisory
will continue for the rest of North Central MT tonight for 
blowing snow. With the strong winds temperatures will not drop 
much, but some cold pockets continue to reside north of Highway 2
from Havre to Harlem where the wind is light, thus some small 
temperature adjustments. Light snow continues around West 
Yellowstone. The advisory will continue for higher elevations of
Southwest MT, with light snow developing overnight mainly over 
the remainder of the mountain areas in Beaverhead and Madison 
counties. 

&&

.SYNOPSIS...
Strong winds along the Rocky Mountain Front and across the 
remainder of Glacier County will continue through the night, 
leading to significant blowing and drifting of snow across these 
areas. Across Southwest Montana and the mountains of Central 
Montana, light to at times moderate snow is expected to develop 
tonight and persist into the day on Saturday. Snowfall 
accumulations over this timeframe and area of two to six inches 
are expected. After a brief lull in the strong winds Saturday 
afternoon, winds will once again begin to increase along the Rocky
Mountain Front and spread east across the plains of North Central
Montana Sunday morning, potentially leading to more blowing and 
drifting of snow.

&&

.AVIATION...
Updated 0548Z.

Northwest flow aloft will continue to prevail over Montana through 
late Saturday evening. Strong and gusty surface winds causing 
blowing snow along the Rocky Mountain Front and over the adjacent 
plains are expected to diminish somewhat by 12Z allowing conditions 
to improve. Disturbance aloft will continue to bring areas of light 
snow to the mountains of the Continental Divide and across southwest 
Montana through the forecast period. Dry conditions continue to 
prevail at lower elevations for widespread VFR conditions at most 
terminals. mpj

&&

.PREV DISCUSSION...
/ISSUED 300 PM MST Fri Feb 23 2018/

This Afternoon through Sunday night...numerous forecast concerns 
through this forecast period which are as follows: 1) Strong winds 
leading to significant blowing and drifting of snow along the Rocky 
Mountain Front and Eastern Glacier through Saturday morning, 2) 
Moderate snowfall accumulations across Southwest Montana and along
the Continental Divide tonight through Sunday night, and 3) 
Strong (potentially) high winds along the Rocky Mountain Front and
over the plains of North Central Montana Sunday morning and 
afternoon, possibly leading to additional blowing and drifting of 
snow.

Surface pressure gradient will continue to strengthen along the 
Rocky Mountain Front through the early morning hours on Saturday as 
a lee-side surface trough sharpens in response to a developing area 
of low pressure across Central Alberta. By the mid-morning hours on 
Saturday, the surface low over Alberta will begin to slide east and 
south into Saskatchewan, which will allow the pressure gradient to 
relax significantly. This relaxation in the pressure gradient will 
allow winds to drop off along the Rocky Mountain Front and over the 
adjacent plains of North Central Montana. For this reason, will keep 
the current end times of 13z for the Blizzard Warning and Winter 
Weather Advisory for blowing/drifting snow as is for the current 
highlighted areas. Continued blowing and drifting of snow is 
expected through the night tonight over the highlighted areas, with 
the most severe impacts within the Blizzard Warning where numerous 
road closures have already occurred today.

A fast moving and energetic shortwave with very impressive H700 
frontogenic forcing will cross Southwest Montana this evening and 
into the day on Saturday. This disturbance looks to bring a quick 
shot of 2-6" for elevations above 6,500ft, which primarily will 
affect mountain passes like Monida, Chief Joseph, Raynolds, and 
Targhee. For this reason, have decided to issue a Winter Weather 
Advisory for Beaverhead, Madison, and Gallatin Counties above 6500ft 
for the expected snowfall, which will likely create some impacts to 
travel over the aforementioned mountain passes due to snow 
covered/slick roadways through Saturday afternoon. After a slight 
decrease in snowfall intensity Saturday afternoon/evening, snowfall 
intensities will begin to increase along the Continental Divide and 
over the mountains of Southwest and Central Montana.
Additional winter weather headlights will likely be needed for
this second wave of accumulating snow, especially across Southwest
Montana and along the Continental Divide.

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. - Moldan/mpj

Monday 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 continue to 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  12  30  15  41 /   0  10  10  20 
CTB  12  31  14  37 /   0  10  10  20 
HLN  14  27  15  39 /  20  20  20  50 
BZN   5  25   9  34 /  20  30  30  30 
WEY  -1  18  -1  21 /  80  60  60  70 
DLN   4  21   4  32 /  20  30  30  50 
HVR   8  25  10  39 /   0  10  10  20 
LWT   8  28  14  38 /   0  10  20  10 

&&

.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.

Winter Weather Advisory from midnight tonight to midnight MST 
Saturday night above 6500 feet for Beaverhead...Gallatin...
Madison.

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

&&

$$

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