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Area Forecast Discussion (AFD)

Issued by Great Falls, MT (TFX)

FXUS65 KTFX 212159

Area Forecast Discussion
National Weather Service Great Falls MT
259 PM MST Wed Feb 21 2018


A somewhat quieter weather pattern will prevail over the next couple 
of days across the area, with any chance of snow mainly confined to 
Southwest Montana. Over the weekend and into next week, a better 
chance of precipitation is possible, although the heaviest amounts 
look to be in the mountains. This pattern also favors breezy to 
windy conditions in the mountains and over the plains, which will 
likely lead to impacts from blowing and drifting snow. Temperatures 
will moderate some over the weekend, then decrease again next



Impacts from blowing and drifting snow will be the primary concern 
through the weekend, then the focus will turn back towards cold 
temperatures and perhaps the return of snowier conditions.

A shortwave diving south through BC at this time will help to 
reinforce the upper level trough in place over the Western US. This, 
in turn, will keep the cold air locked in place locally through 
Friday. The BC shortwave will close off over OR/ID, focusing the 
greatest lift/moisture to our south and west. However, there should 
be enough moisture for some snow showers/areas of light snow, 
primarily along/south of I-90, but with minimal impact. 

Over the weekend, zonal flow will lead to increasing winds aloft 
over the area. This will combine with a tightening pressure gradient 
within a developing lee-side trough and steep lapse rates to produce 
a more widespread area of breezy/windy conditions. At this time, 
high wind criteria is not expected, although this potential will be 
closely monitored. However, what is expected is a more widespread 
blowing/drifting snow potential, especially with cold temperatures 
and snow appearing to still be loose enough to blow around. At this 
point, we will let the current Winter Weather Advisory for blowing 
snow cover the ongoing impacts along the Rocky Mtn Front through 
this evening. Additional winter weather products for blowing snow 
certainly seem likely over the weekend, especially Friday and again 
Sunday. It should be noted that blowing snow has led to significant 
impacts along the Rocky Mountain Front in recent weeks and 
conditions look to go downhill once again in that area. If the snow 
is loose enough, ground blizzard conditions are a distinct 
possibility along the Rocky Mountain Front where gusts of 40-60 mph 
are expected. Elsewhere over the plains, the winds do not look 
nearly as strong, but still strong enough to cause impacts to 
travel. Those with interests along the Rocky Mountain Front are 
encouraged to pay attention to later forecasts and statements 
regarding the ongoing/additional blowing snow impacts. 

With the windy conditions, a brief moderation in temperatures is 
expected, especially by Sunday, but many locations may still not 
reach the freezing mark, especially along the Hi-line. Over the 
weekend and into next week, a couple of shortwaves will bring 
accumulating snow to the mountains. For the plains and valleys, each 
shortwave may allow some snow showers to develop, but widespread 
accumulating snow at lower elevations doesn't look likely at this 
point. MARTIN


Updated 1735z.

VFR conditions expected today. Reductions in VIS/CIGs possible 
tonight due to BR/FZFG.

Clouds continue to decrease across much of the forecast area at this 
time as an upper level trough pushes away from the area. Across SW 
MT, clouds will linger longer, though, and a few SHSN are possible 
this afternoon. With high pressure building in tonight, and low 
temps falling below or well below expected afternoon dewpoint temps, 
BR/FZFG appears likely across parts of the area, especially Central 
MT where they may be less cloudcover. For now, I have covered this 
potential with a VCFG mention, but this potential will continue to 
be further evaluated in later forecasts. IFR/LIFR VIS/CIGs would be 
possible with any BR/FZFG. SHSN will once again remain possible 
across SW MT on Thursday. MARTIN


GTF  -8  13  -7  22 /   0   0  10   0 
CTB  -9  14  -8  21 /   0   0  10   0 
HLN  -3  18  -2  23 /   0  10  20  10 
BZN  -3  20  -2  21 /  10  10  20  10 
WEY -10  19  -9  19 /  70  20  20  20 
DLN  -3  16  -2  19 /  20  10  30  10 
HVR -17   7 -12  15 /   0   0  10   0 
LWT  -5  16  -7  23 /   0   0  10  10 


Winter Weather Advisory until 8 PM MST this evening Northern 
Rocky Mountain Front.