Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 162155

255 PM MST Tue Dec 16 2014

Tonight through Thursday...Relatively quiet conditions over
central and north central Montana during the period. Areas of
freezing fog continue to cover portions of north central Montana
this afternoon...and those areas that did burn off will likely
see the fog redevelop late this afternoon or this evening. Have
extended the Freezing Fog Advisory for most of north central
Montana until 11 a.m. Wednesday.

Upper air pattern shows a high pressure ridge over the Rocky
Mountain states with a low pressure trough over the west coast.
Idiosyncrasies in the pattern are resulting in a split flow aloft
over southwest and central Montana...and small weather systems
embedded in the flow, and being steered into Montana, are being
sheared apart and weakened. Best chance for snow from these
systems will be over the southwest Montana mountains. Probabilities
decrease to only slight chances as the system moves to the
northeast over central Montana. As the high pressure ridge shifts
east and the trough begins to move inland, another system will
approach the area during the day Thursday. This again brings slight
chances for snow mainly over the west and southwest mountains.
Temperatures will remain near seasonal averages for this time of

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. Coulston


This is a very low confidence forecast with respect to ceilings and
visibilities. Do have fair confidence that areas of light snow will
spread into southwest Montana late this afternoon then reach the
Canadian border early Wednesday morning. Conditions for KGTF and
KCTB and KHVR could range from VFR to LIFR at anytime at least into
early Wednesday morning. Then for KBZN and KHLN and KLWT conditions
could range from VFR to IFR at any time after 00Z. Also have fair
confidence that conditions will be mostly VFR at 18Z Wednesday. Blank


GTF  21  37  25  37 /  20  30  10  10
CTB  17  34  22  36 /  10  20  10  10
HLN  20  31  18  33 /  30  20  10  20
BZN  22  31  14  30 /  30  30  10  20
WEY  22  31  17  28 /  50  40  20  30
DLN  20  33  17  33 /  30  20  10  20
HVR  15  31  19  35 /  10  20  20  10
LWT  21  38  22  39 /  20  20  10  10


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


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