Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 212348
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
447 PM MST Fri Nov 21 2014

...Wintry mix of weather possible over the plains of North
Central Montana tonight into Saturday morning...
...Strong winds and blowing snow in the mountains overnight into
Saturday evening...

.DISCUSSION...

Tonight through Sunday...A Pacific weather system will move into
Montana from the west tonight and through North Central/Southwest
Montana on Saturday. It will initially bring measurable snow to
the mountains tonight and the already strong winds there will
cause areas of blowing snow. Will therefore be continuing the
Winter Weather Advisory for those mountain areas, as well as the
High Wind Warning for the Rocky Mountain Front. Southerly winds
through the Norris Hill area may approach High Wind criteria, but
will monitor the situation for now. Have also delayed the
beginning of the High Wind Watch for eastern Glacier County until
Saturday morning. Winds just off the surface appear strong enough
to cause high winds, but the mechanism to bring them down remains
somewhat in doubt. The pressure gradient increases during the day
on Saturday, which looks like the best time, if any, for strong
winds. Will allow subsequent shifts to further analyze it. As the
precipitation moves into the valleys and onto the plains
overnight, there will be a warm layer of air just off the surface
as temperatures fall to near or slightly below freezing at the
surface. This may cause sleet or freezing rain to fall for periods
of time after midnight and into Sunday morning, mainly east of a
Cut Bank to Great Falls line, but also in some of the southwest
valleys. However, the chance for significant precipitation is low
and surface temperatures will likely not rapidly cool (which would
cause ice accumulation on surfaces), so am not expecting
widespread significant impacts and will not be issuing any
advisories for this area at this time. However, the situation will
need to be monitored. Regarding the snow, though, it looks like
the Big Belt and Little Belt mountains will likely receive a few
inches of snow, which would cause travel difficulties over Kings
Hill Pass and through Deep Creek Canyon, so have issued a Winter
Weather Advisory for those areas beginning early Saturday morning
and continuing through Saturday night. As the system exits the
area Saturday night into Sunday, winds will decrease somewhat and
the resulting northwesterly flow aloft will bring cooler
temperatures and a continued chance of light snow showers to much
of the forecast area. Temperatures should only fall to a few
degrees below normal and little if any significant snow
accumulation is expected.
Coulston

Sunday night through Friday...Unsettled weather continues into
the long term forecast as a shortwave trough moves through the
region with northwesterly flow aloft. This should allow for cool
temperatures and snow showers mainly over the higher terrain to
continue into the work week. Model agreement begins to break down
by Tuesday morning when the GEM and ECMWF push a large scale
ridge further into the Rocky Mountains, the GFS however keeps the
ridge back off the Pacific coast, and suggests a significantly
cooler solution through the rest of the work week. Have trended
toward a warmer and less wet solution. Did not want to buy
completely into the ECMWF but have enough confidence to at least
trend temperatures up a bit and PoPs down. Suk/Emanuel

&&

.AVIATION...
UPDATED 2343Z.
Strong west flow aloft will strengthen further during the night
ahead of a low pressure trof over the West Coast. A cold front will
cross the Rockies early Saturday morning and spread east during the
day. Snow, mountain obscuration, and IFR/LIFR conditions are likely
at higher elevations later tonight and Saturday. Elsewhere, VFR
conditions will prevail. Very strong and gusty winds will also be
associated with and after frontal passage, and gusts in excess of 60
kts are expected over and along the lee slopes of the Rockies.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  33  44  26  38 /  10  20  10  10
CTB  29  40  23  35 /  20  20  20  10
HLN  31  44  28  38 /  20  50  20  20
BZN  25  41  19  33 /  20  70  20  20
WEY  22  33  10  24 /  80 100  70  40
DLN  28  39  19  31 /  30  70  20  20
HVR  27  43  25  34 /  30  30  40  20
LWT  29  46  26  35 /  20  40  30  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING until 10 PM MST Saturday Northern Rocky
Mountain Front...Southern Rocky Mountain Front.

WINTER WEATHER ADVISORY from Midnight tonight to 5 AM MST Sunday
Central and Southern Lewis and Clark...Northern Rocky Mountain
Front...Southern Rocky Mountain Front.

WINTER WEATHER ADVISORY from 6 AM Saturday to 5 AM MST Sunday
For US 89 over Kings Hill Pass.

WINTER WEATHER ADVISORY from Midnight tonight to 5 AM MST Sunday
Beaverhead...Gallatin...Madison.

HIGH WIND WATCH from Saturday morning through Saturday evening
Eastern Glacier.

&&

$$

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