Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 181348

648 AM MST Thu Dec 18 2014


The freezing fog advisory has been extended until 11am and shifted
further east to include Blaine county and the Missouri Breaks. Fog
has eroded with westerly winds along the Rocky Mountain Front and
the Helena Valley, so the fog advisory was dropped in these areas.


The airmass is again rather stagnant will ample low-level moisture.
An approaching shortwave should  increase winds and help dry lower
levels. Areas of dense fog are possible across northern portions of
Central Montana. Locally dense fog has also been noted in the Helena
Valley. Local IFR/MFR conditions will last until mid-morning. VFR
conditions are generally expected afterwards.


/ISSUED 440 AM MST Thu Dec 18 2014/

Today through Saturday...Weak low pressure continues over Central
Montana and dynamics are also weak. To the west, an upper level
ridge will build over the Pacific Northwest. A low levels, a A low
pressure trof sits along the lee of the Rockies...just about over
Cut Bank. This surface trof should finally move east and west winds
will return to the northwest zones, and fog should only be a problem
farther east. The ridge will move over the Idaho Panhandle tonight
and moisture behind the ridge will move into the region late
Thursday night ahead of an approaching shortwave. This weak
shortwave will move quickly and not leave much time for weather to
development. Best chance for precipitation will be over the Rockies
and Southwest Montana.  A Pacific cold front associated with the
shortwave will cross the Rockies late Friday and Friday night. This
will bring some cooling across the zones Saturday although breezy
conditions and sun should keep max temps inline with previous days.

Saturday Night through Thursday...Through Monday, an upper level
high pressure ridge will strengthen over the eastern Pacific Ocean
and an upper level low pressure trough will deepen over central
Canada and the northern CONUS plains. The resulting strong
northwesterly flow aloft will bring increasing westerly surface
winds to the forecast area. Although forecast models are not quite
as strong with these winds as they have been the last couple of
nights, there is still a chance for High Wind criteria winds along
the Rocky Mountain Front and over some ridge tops. Will continue to
monitor this for potential High Wind highlights. This increasing
flow aloft will also bring warm and moist Pacific air and a weak
disturbance into the area. The main impact from this will be at
least a rain/snow mix in the mountains, if not mostly rain, while
the plains and valleys will have less of a chance of precipitation.
This could be a concern in the mountains with regard to rain
possibly falling on snowpack. Will monitor this situation for
potential hydrologic highlights. With the warm air aloft moving over
cooler air at the surface over the plains of north central Montana
Saturday night into Sunday morning, have included a slight chance of
freezing drizzle there. The westerly downslope winds will quickly
spread east across the area during the day on Sunday, warming
temperatures well into the 40s by afternoon. Temperatures will
remain similarly mild through Monday. As the disturbance exits the
area Monday night, the chance for precipitation will be limited to
the mountains into Tuesday. However, a weak cold front will move
south through the area on Tuesday, cooling temperatures to near
seasonal averages. As was mentioned yesterday, a cold and moist
weather system will move southeast from the Gulf of Alaska and into
the northern Rockies for Wednesday (Christmas Eve Day) into Thursday
(Christmas Day). There is still a good chance of precipitation with
this system across the area, but forecast models are trending a bit
farther south with the heaviest precipitation, focusing it more over
southwest Montana than central Montana. Have therefore made this
adjustment to the forecast. There is still a good indication that
temperatures will cool significantly below normal through this
period, for widespread light snow. Will continue to monitor the
progress of this system for potential winter weather highlights, as
this system will likely negatively impact holiday travel. Coulston


GTF  41  27  41  28 /  10  10  10  20
CTB  38  24  39  28 /  10  10  10  10
HLN  35  20  36  22 /  10  10  20  30
BZN  32  17  33  19 /  10  20  20  40
WEY  32  20  33  23 /  30  40  40  50
DLN  35  20  38  22 /  10  10  20  30
HVR  37  21  39  26 /  10   0  10  20
LWT  43  24  44  27 /  10  10  10  30


FREEZING FOG ADVISORY until 11 AM MST this morning Blaine...


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