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FXUS65 KTFX 241142

Area Forecast Discussion
National Weather Service Great Falls MT
442 AM MST Sat Feb 24 2018

...Update to Aviation...


Windy conditions will continue to cause areas of blowing snow with
blizzard conditions expected along the Rocky Mountain Front and
over the adjacent plains Saturday morning and again on Sunday. 
Pacific moisture in a northwest flow aloft will also bring areas 
of snow to the mountains along the Continental Divide and in 
southwest Montana today through Monday. Lower elevations will
remain mostly dry through the weekend.



Today through Monday...Montana continues to reside beneath upper
level troughing with a complex surface pattern causing multiple
impacts across the forecast area. Strong and gusty winds will
continue along the Rocky Mountain Front and in eastern Glacier
County this morning causing widespread blowing/drifting snow and
closing multiple roads. Have gone ahead and extended the ending
time for the existing Blizzard Warning through noon. Winds are
expected to diminish for 12 to 18 hours or so beyond this time
before increasing again. Ideally, the warning will be dropped
today, but as surface winds begin to increase again overnight I
anticipate that another Blizzard Warning could be required for 
Sunday. This next blast of strong winds could see gusts exceed 90
mph in favored canyons, valleys, and passes of the Rocky Mountain
Front from early Sunday morning through late Sunday evening. 
These strong winds will likely spread out across the plains as 
well and there is some likelihood that conditions over the plains 
could require highlights for high winds as well as blowing snow. 
Meanwhile, the existing Winter Weather Advisory for higher 
elevations of southwest Montana will remain in effect through 
midnight tonight with about 2 to 4 inches of accumulation likely. 
Am anticipating that this area should see a lull in precipitation 
from midnight tonight through about noon on Sunday, then another 
surge of moisture will bring additional snowfall to this region 
from Sunday afternoon through late Monday afternoon. Once again, I
anticipate that additional winter weather highlights will be 
required for my southwest Montana zones with this next surge.
Biggest wild card in all of this activity will be high
temperatures for Sunday. Some models suggest that portions of the
forecast area could see temperatures actually rise back above
freezing for the first time in awhile on Sunday afternoon. This
could end up causing blowing snow to be less than anticipated.
However, any warmup will be short-lived as models bring highs back
below freezing again on Monday. mpj

Monday Night through Saturday...Medium range forecast models are in 
much better agreement with the forecast solution during this period 
than they were last night. A broad upper level low pressure trough 
over the western and central portions of Canada and the United 
States is still forecast to be the dominant feature through this 
period. One embedded shortwave trough will exit the state Monday 
night, then another shortwave will swing through Montana Tuesday 
through Tuesday night, resulting in periods of light mountain snow. 
A shortwave high pressure ridge will then move into the state for 
Wednesday through Thursday ahead of a deep upper level low pressure 
area. This ridge will help decrease the chance of snow over the 
mountains, while breezy westerly downslope winds help keep the lower 
elevations dry. The low pressure area will be off the Pacific 
Northwest coast Thursday through Friday, but forecast models differ 
on what to do with it after then; the Canadian model keeps it off 
the coast, the ECMWF moves it slowly into the Pacific Northwest, and 
the GFS moves it quickly into Montana. Will go closer to the 
GFS/ECMWF solution of bringing the low towards the forecast area for 
an increasing chance of snow for Friday through Saturday. However, 
this solution is fairly different than the forecast depicted last 
night, so confidence in the details of this part of the forecast is 
only low to moderate. Regardless, the overall temperature trend 
keeps temperatures between 5 and 10 degrees below normal through 
Thursday, with the potential for at least a minor cooldown for 
Friday and Saturday.


Updated 1142Z.

Northwest flow aloft will continue to prevail over Montana through 
early Sunday morning. Strong and gusty surface winds causing blowing 
snow along the Rocky Mountain Front and over the adjacent plains 
should diminish somewhat by 18Z 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 expected at lower 
elevations for prevailing VFR conditions at most terminals. mpj


GTF  28  15  36  13 /  10  10  20  20 
CTB  27  15  33  11 /  10   0  20  10 
HLN  28  12  35  12 /  20  20  50  40 
BZN  26   7  32  12 /  30  30  30  50 
WEY  17  -1  20  11 /  80  70  80  90 
DLN  22  10  29  11 /  40  30  30  60 
HVR  24  11  33  10 /  10  10  10  10 
LWT  28  16  33  14 /  10  20  20  20 


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 until midnight MST tonight above 6500 
feet for Beaverhead...Gallatin...Madison.

Blizzard Warning until noon MST today Eastern Glacier...Northern 
Rocky Mountain Front...Southern Rocky Mountain Front.

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