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000
FXUS65 KTFX 120540
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
945 PM MST Wed Dec 11 2013

UPDATED AVIATION SECTION

.DISCUSSION...
Main update this evening is to add mention of snow to the
mountains east of the Continental Divide overnight. A weak
shortwave moving through the westerly flow aloft has brought a few
showers to the mountains, while lower elevations are only
reporting slightly lowering cloud ceilings. Am not expecting much
additional accumulation in the mountains, though. Otherwise,
forecast appears to generally be on track. The breezy westerly
winds have kept temperatures this evening a bit warmer than
previously expected over the plains of north central Montana.
However, am expecting enough of a drop off in winds to allow
temperatures to fall into the 20s for at least a brief period of
time. Windy conditions will likely continue areas of blowing snow
along the Rocky Mountain Front overnight, so will continue the
High Wind Warning and Winter Weather Advisory for blowing snow
there for now. With less wind in the southwest valleys,
temperatures have dropped into the single digits already in the
Bozeman area this evening. Temperatures should fall more slowly
there through the rest of tonight, keeping lows there in the lower
to mid single digits. Coulston

&&

.AVIATION...
UPDATED 0545z.
Northwest flow aloft will continue over the area as an upper ridge
remains over the Pacific Northwest. Moisture moving down the front
of the upper ridge continues to bring mid and high clouds across the
area overnight. A lee side trof will allow gusty surface winds to
continue. The strongest winds will be along the Rocky Mountain Front
and adjacent plains, though wind speeds should decrease some after
09z. VFR conditions prevail though MVFR conditions are possible
along the Rocky Mountain Front due to areas of blowing snow.

&&

.HYDROLOGY...
The flood advisory for the Gallatin River near Gallatin Gateway
will continue until the threat from flooding has ended. The ice
jam in that area is still in place and has been slow to break up.
While the river level has gone down slightly, water is still
slowly flowing out of the river in spots, and standing water
remains in some fields and around some houses. Reports from the
area indicate that roads have been opened, as the water has
ceased flowing over the roads, but they remain quite icy, causing
continued hazardous driving conditions in spots. High
temperatures will reach at least a few degrees above freezing
through the weekend, increasing the chance for ice jam breakup,
but overnight temperatures will fall well below freezing. Impacts
have at least temporarily lessened, but advisory will remain in
place for the time being. Coulston

&&

.PREV DISCUSSION...
/ISSUED 445 PM MST Wed Dec 11 2013/
Tonight through Friday...An upper ridge over the Pacific
Northwest will weaken as it moves over the forecast area
Thursday. Several weak weather disturbances aloft will follow
Thursday night and Friday. Moisture will be increasing but lift
is not particularly impressive with the disturbances. Through
Thursday it appears the only threat of snow will be over the
mountains of the Rocky Mountain Front. Thursday night and Friday
expect periods of snow over the mountains of the Rocky Mountain
Front with scattered snow over other mountains and a slight
chance to chance of snow for the plains and valleys. At the
surface cooler Canadian air will move into north central Montana
Thursday night but models differ on how far to the southwest the
cooler air will spread. This will result in low confidence for
forecast highs on Friday. As for weather highlights will continue
the high wind warning for the Rocky Mountain Front. Strongest
winds aloft should occur Thursday afternoon then diminish during
the evening. Will continue the winter weather advisory for
blowing snow for the Rocky Mountain Front through Thursday
morning. Elsewhere over the east slopes will cancel the winter
weather advisory for blowing snow. Temperatures have risen to
near or a little above freezing which has resulted in some
settling of the snow. A check of web cameras does not show much
in the way of visibility restrictions. Blank

Friday through Tuesday...
An upper level high pressure ridge will be over the Eastern
Pacific Friday with northwest flow aloft over the zones. A low
pressure shortwave will move through this flow early Friday and
move east of the region by Friday night. High pressure will
rebuild aloft late Friday and Friday night although several
disturbances will continue to move through the flow aloft through
the rest of the period. This will keep the air mass unsettled
along with a chance for precipitation. A fairly strong shortwave
will move through the Pacific Northwest Saturday and this will
deepen a surface low pressure trof along the lee of the Rockies.
Strong winds should develop across the Rockies and adjacent
plains. Winds will weaken at times however the period of strong
winds could last through Tuesday. Temperatures will begin the
period rather cool and remain below normals Friday but trend above
normals by Saturday with the warmest temperatures of the period
occurring on Sunday. Zelzer

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  24  42  23  38 /  10   0  10  20
CTB  22  38  16  33 /  10   0  10  20
HLN  14  35  18  34 /  10   0  10  30
BZN   5  33  15  34 /  10   0  10  30
WEY  -2  25   3  24 /  10   0  20  40
DLN   9  33  15  34 /   0   0  10  20
HVR  14  32   9  25 /  20  10  10  30
LWT  19  44  20  37 /  20   0  10  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING until 11 PM MST Thursday Northern Rocky
Mountain Front...Southern Rocky Mountain Front.

WINTER WEATHER ADVISORY until 6 AM MST Thursday Northern Rocky
Mountain Front...Southern Rocky Mountain Front.

FLOOD ADVISORY until further notice for the Gallatin River near
Gallatin Gateway.

&&

$$


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