Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 161726

1026 AM MST Tue Dec 16 2014

Minor update to the forecast for today. With light wind, and layer
of clouds, believe atmospheric mixing will be minimal and
temperatures will have a tough time warming today. Widespread
areas of fog continue. Freezing Fog Advisory remains in place and
may need to be extended. Pulled back on afternoon high
temperatures across much of north central and central Montana.
Also added mention of Freezing Fog redeveloping later this afternoon
and this evening.

Remainder of forecast on track with areas of snow showers
developing over southwest and working into central Montana later
today and tonight.

Low clouds with areas of dense fog will likely begin to erode
somewhat after 16Z across the plains of north central today.
Ceilings will mostly be IFR/LIFR, but the dense fog over the
western plains (including KGTF KCTB) is causing VLIFR conditions.
Conditions should improve in the west first, then ceilings will
gradually lift and clouds will break up after 18Z. However, KLWT is
out of the fog/low clouds at this time, and they will likely stay
that way. A disturbance will move northeast into the area after 00Z,
bringing increasing high and mid level cloudiness from the southwest
after 18Z, then more mid level cloudiness and a chance of snow after
03Z in the southwest and after 06Z over central Montana. Occasional
MVFR conditions are possible with any snow.


/ISSUED 510 AM MST Tue Dec 16 2014/

Today through Thursday...Forecast for the short term period is
expected to remain foggy this morning. Have expanded the Freezing
Fog Advisory to include Cascade and Judith Basin Counties as well
as the Rocky Mountain based on latest observations and SPORT night
time microphysics RGB imagery. Shortwave energy is still on track
to push into southwest Montana today and then into central Montana
overnight. Have increased PoPs across portions of the forecast
area based upon NAM model run but do not anticipated that snowfall
will be widespread enough or heavy enough to require any type of
highlights. Temperatures will remain near or below seasonal
averages for this time of year but I have undercut office-derived
SuperBlend temperature guidance for today and Wednesday given poor
performance on Monday. Expect another lull in clouds and
precipitation Wednesday night into Thursday before the progressive
pattern aloft brings another shortwave into western portions of
the forecast area Thursday afternoon. mpj

Thursday Night through Tuesday...A weak upper level ridge of high
pressure will keep the forecast area mostly dry Thursday night and
Friday. A shortwave trough will then move into the area Friday night
into Saturday, bringing an increased chance of mountain snow.
However, breezy westerly downslope winds will keep the plains dry.
The weather pattern will change somewhat beginning on Sunday. An
upper level ridge of high pressure will strengthen off the
California coast and an upper level trough of low pressure will
deepen from Hudson Bay into the Great Lakes. This will put Montana
under the influence of a strong northwesterly flow aloft. The
strongest winds aloft (60 to 70 kt at 700 mb) will occur Sunday into
Monday with the passage of a disturbance embedded in the flow. This
set-up will bring gusty westerly downslope winds to much of the
area, but especially over the plains of north central Montana. In
fact, some areas along the Rocky Mountain Front could approach High
Wind criteria (40 mph sustained/58 mph gusts). Confidence is
increasing that High Wind highlights may be needed for this event.
There is also significant moisture with this disturbance, so have
increased the chance for precipitation out onto the plains. Although
the winds will decrease somewhat after the passage of the
disturbance, the northwesterly flow aloft will remain fairly moist,
so have kept the chance for precipitation above climatological
normals across the area into Tuesday. The breezy winds throughout
the period will keep temperatures around 10 degrees above normal.
The warmest day of the period appears to be Monday, when most lower
elevation locations should get well into the 40s.


GTF  28  22  36  24 /   0  20  30  10
CTB  25  17  34  21 /   0  10  10  10
HLN  30  20  32  19 /  10  30  20  10
BZN  29  19  33  15 /  10  30  20  10
WEY  29  18  31  14 /  40  50  40  20
DLN  31  21  34  19 /  20  30  10  10
HVR  26  15  30  20 /   0  10  20  10
LWT  30  22  37  21 /   0  20  20  10


FREEZING FOG ADVISORY until 11 AM MST this morning Cascade...
Eastern Glacier...Eastern Pondera...Eastern Teton...Judith
Basin...Northern Rocky Mountain Front...Southern Rocky Mountain


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