Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 250541

Area Forecast Discussion
National Weather Service Great Falls MT
1041 PM MST Sat Feb 24 2018

...Update to Aviation...


Surface observations reveal little in the way of accumulating new
snow across Southwest MT this evening. Satellite imagery shows the
upper level trough axis through Beaverhead county, moving quickly
to the east. The winter weather advisory for this area will remain
in effect for now, but expect it to expire routinely at midnight
if not cancelled earlier. Missoula radar indicates numerous snow
showers extending upstream, so additional snow accumulation can`t
be ruled out this evening. Water vapor imagery shows subsidence
with clearing skies across North-central MT. Observed temperatures
were already nearing forecast lows, so overnight temperatures were
adjusted lower to better match these observed trends. One
additional point of interest is that we continue to see reports of
blowing and drifting snow across roads within our northeast
counties. These counties were not as warm, nor did they experience
the intensity of blowing snow see elsewhere yesterday. Hence,
even fairly light winds may continue to drift snow, so anyone
driving into northeast MT overnight should continue to use caution
and expect variable conditions. The rest of the forecast remains
in good shape overall, with strong winds returning Sunday with the
potential for another round of widespread drifting and blowing
snow. PN



Periods of light snow are possible Saturday evening across
Southwest Montana. Strong west winds return on Sunday, creating
areas of blowing snow across much of North-central Montana.
Travel west over the Continental Divide will be difficult on
Sunday due to a combination of falling and blowing snow.


Updated 0541Z

Variable mid- and high-level clouds will prevail across Montana
overnight through late Sunday evening. Areas of snow remain possible
across southwest Montana through the forecast period for IFR/MVFR
conditions and mountain obscurations at times. Widespread VFR
conditions prevail over north-central and central Montana but strong
and gusty westerly winds will cause localized IFR/MVFR conditions in
blowing snow, especially along the Rocky Mountain Front. mpj


/ISSUED 454 PM MST Sat Feb 24 2018/

Tonight through Monday...Radar and satellite imagery shows an area
of light snow beginning to spread across Southwest Montana. Light
snow will continue this evening, then end by the early morning
hours. A winter weather advisory is in effect for Southwest
Montana this evening to address expected impacts to travel over
mountain passes. New snow accumulations of around 1-4 inches are
possible. Light snow showers are also seen moving into Hill and
Blaine counties. These are expected to move quickly and produce
little new snow accumulation.

Strong west winds return along the Rocky Mountain Front early
Sunday, then spread across the North- central plains through the
day Sunday. Travel over the continental divide will be difficult
Sunday due to a combination of falling and blowing snow. The
previous Winter Storm Watch has been converted to a Winter Weather
Advisory for blowing snow. Winds gusting 35 to 50 mph will cause
widespread blowing and drifting snow. Localized wind gusts to 70
mph are possible along the immediate east slopes of the Rocky
Mountain Front. Warmer temperatures, combined with the intense
scouring and compaction of existing snow cover that occurred
Friday provides reserved confidence that ground blizzard
conditions will not redevelop over western Glacier County.
However, this remains a sensitive area in critical snow recovery
operations, so will monitor carefully for any blowing snow
conditions that may develop on Sunday. Winds speeds decrease
Sunday night. Another shortwave tracks through Southwest MT on
Monday, providing a new round of light snow that could slow travel
in some areas Monday evening.

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.


GTF  12  34  14  30 /  10  20  20  10
CTB  13  31  10  29 /  10  20  30  10
HLN  14  33  16  29 /  20  40  30  20
BZN   8  31  17  28 /  30  30  40  40
WEY   0  20  13  25 /  80  80  80  60
DLN   6  26  13  25 /  20  30  50  30
HVR   8  31  11  24 /  10  10  10  10
LWT  10  31  17  28 /  10  10  20  10


Winter Weather Advisory from midnight tonight to midnight MST
Sunday night Central and Southern Lewis and Clark...Northern
Rocky Mountain Front...Southern Rocky Mountain Front.

Winter Weather Advisory from 6 AM Sunday to midnight MST Sunday
night Blaine...Cascade...Chouteau...Eastern Glacier...Eastern
Pondera...Eastern Teton...Fergus...Hill...Judith Basin...

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


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