Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 201738
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1040 AM MST Sat Dec 20 2014

...UPDATE TO AVIATION...

.UPDATE...

Only minor updates issued this morning to bring today`s forecast
closer to observed trends. The High Wind Warning remains in effect
along the Rocky Mountain Front. As expected, wind gusts in that
area have dropped to around 30 to 45 mph. Wind gusts will increase
again early Sunday. Strong winds are still expected to spread east
across the adjacent plains on Sunday, but confidence is lower that
gusts will reach 50kts/58mph in the High Wind Watch area. Remainder
of the forecast package is on track with snow developing over the
mountains tonight and Sunday, and rain or snow at lower elevations.
Decisions are pending regarding the status of the High wind watch
and the Winter Storm Watch. Nutter


&&

.AVIATION...
UPDATED 1740Z.
A moist west to northwesterly flow aloft will bring broken mid to
high level clouds and breezy conditions to the forecast area today
through late this evening. Widespread VFR conditions will prevail
through 06Z Sunday. However, a wet storm system will push into
western and southwest Montana overnight bringing widespread snows
for MVFR conditions and mountain obscurations. The KBZN terminal
will likely see snow develop around 08Z Sunday with snow expected to
prevail through the end of the forecast period. Strong winds aloft
could also produce local mountain wave turbulence through much of
the period. mpj

&&

.PREV DISCUSSION...
/ISSUED 445 AM MST Sat Dec 20 2014/

Today through Monday...A strong upper level jet will move across the
Rockies today and eventually mid-level winds will increase to 50+
knots during the night. A high wind warning is currently in effect.
Strongest winds are expected tonight through Sunday morning. Also of
concern is the possibility of very strong winds spreading east
across the adjacent plains tonight and Sunday. A weak upper level
disturbance will move east of the region today while to the west, a
low pressure trof will approach the West Coast. Surface low pressure
is over the Albert/Saskatchewan border with a tight surface pressure
gradient along the slopes of the Rockies. Brisk winds will continue
today and strengthen tonight with the approach of the jet aloft. The
airmass will be slightly cooler today behind the trof but strong
winds will moderate the effect somewhat. A low pressure trof will
move over the West Coast late today and moisture ahead of this
system will spread across the Rockies and through the zones. Flow
will generally remain strong and out of the west although heights
will be slowly falling through the night. Decent lift will develop
Saturday night along with widespread precipitation. Northern
portions of the CWA will be warm enough for rain. Southwest Montana
will see mostly snow. Accumulations will generally be marginal at
lower elevations with only the higher elevations expected to receive
significant amounts. Flow will remain unsettled through Monday
although the heaviest snowfall will be tonight and Sunday. Zelzer

Monday night through Saturday...Shortwave ridge will develop over
the region Monday night into Tuesday afternoon...resulting in just a
passing shower and seasonable temperatures. For late Tuesday night
through Christmas Day...expect a Pacific storm system to affect much
of the region. The track of this storm is similar to
yesterday...with areas west of a line from Cut Bank to Lewistown
generally seeing 2 to 5 inches of snow at lower elevations and 6 to
12 inches in the mountains. For areas east of this line...generally
snow accumulations will be less than inch. (Interesting...that the
record snowfall for Great Falls on Christmas is only
4.4 inches...and we might have a chance at that record should the
heavier snowband move through Great Falls.) Overall this is not a
major storm...but the timing of this storm during a major holiday
period will affect travel. Temperatures will also begin a cooling
trend from Wednesday through Friday. There is the chance that
temperatures on Christmas Day could be a bit colder than currently
forecast because of clouds/snowfall. After this storm exits the
region late Thursday/early Friday...the weather pattern will become
a bit less active. There will be a small chance for a passing snow
shower over the weekend and into the New Years week...but no
significant snowfall is expected at this time. The main concern
tonight is the GFS13/EC are hinting at some very cold air moving
into the region by Tue Dec 30th...again this is a ways out...and
things can chance a bit...but at this time current models are trying
to bring down another batch of arctic air before New Years. Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  44  36  46  32 /  10  30  50  30
CTB  41  31  41  30 /   0  20  40  30
HLN  40  31  44  32 /  10  50  60  40
BZN  38  31  42  26 /  10  70  80  60
WEY  34  29  36  23 /  40  90  80  80
DLN  39  35  43  30 /  10  60  70  60
HVR  42  26  42  26 /  30  30  60  30
LWT  44  31  44  31 /  10  30  80  40

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY from 5 PM this afternoon to 5 AM MST
Monday FOR ELEVATIONS ABOVE 5000 FEET FOR Central and Southern
Lewis and Clark...Jefferson...Northern Rocky Mountain Front...
Southern Rocky Mountain Front.

HIGH WIND WATCH from late tonight through Sunday afternoon
Eastern Glacier...Eastern Pondera...Eastern Teton...Liberty...
Toole.

HIGH WIND WARNING until 5 PM MST Sunday Northern Rocky Mountain
Front...Southern Rocky Mountain Front.

WINTER STORM WATCH from 5 PM MST this afternoon through late
Sunday night FOR ELEVATIONS ABOVE 6000 FEET FOR Beaverhead...
Gallatin...Madison.

&&

$$

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