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Area forecast discussion 
National Weather Service Great Falls Montana
425 PM MST Thu Nov 20 2014

Aviation section updated.

Discussion...

Today through Saturday...a weak shortwave will cross The Rockies and
central Montana late tonight and Friday while, to the west, a strong
upper level jet will move over the West Coast. A high pressure ridge
over central Montana will be flattened by a series of shortwaves
ahead of a low pressure trof in the eastern Pacific. These
disturbances will maintain a Lee trof along the slopes of The
Rockies and a strong surface pressure gradient. Winds will remain
brisk through the period across The Rockies and adjacent plains and
become very strong Friday night and Saturday. Winds across southwest
Montana will not be nearly as strong as those over the plains
although, as the upper level winds strengthen ahead of the
approaching trof, strong winds will also spread across the area
Friday night and Saturday. The trof will be over the Pacific
northwest by early Saturday morning and good lift will develop ahead
of it across The Rockies. Snow over The Rockies will increase as the
low pressure trof approaches and a Winter Weather Advisory for snow
and blowing snow will be issued beginning Friday night. The upper
level trof will be over The Rockies by late Saturday although the
cold air aloft will still be west of The Rockies. Zelzer

Saturday night through Thanksgiving...period begins with a mid level
trough moving across Montana and surface low pressure tracking east along
and just north of the Montana/Canadian border Saturday night. Cold
advection, favorable upper level jet dynamics and slightly
unstable/cyclonic flow aloft will keep a chance for snow showers
across central/SW Montana while moisture wrapping around the low-mid
level circulation center passing by to the north will bring a chance
of snow showers to portions of north central Montana. Northwest flow aloft
continues Sunday into next week with a period of drier conditions
likely late Sunday through Monday. By Tuesday, flow aloft buckles in
response to shortwave energy coming onshore, allowing the upper
level jet to lift north into the northern rockies for increasing
chances for precipitation. This is where models begin to diverge
significantly as the European model (ecmwf) model brings in a stronger shortwave
trough from the NW, carving out a trough over the interior west with
a much colder Canadian airmass moving into the region Wednesday and
Wednesday night. However the GFS model continues to build upper
level ridging inland Wednesday and Thursday, resulting in a shorter
lived precipitation event with warmer temperatures overall.
Confidence remains low at this point with regard to cold air
intrusion next week, but initial push of moisture/precipitation
Tuesday appears more likely regardless of model solution and have
increased pops that period. Hoenisch

&&

Aviation...
updated 2325z.
Variable mid- and high-level clouds will pass through north-central
and southwest Montana. Southwest to west surface winds will increase
this evening and remain strong through the period. The strongest
winds will occur along the Rocky Mountain front and over adjacent
plains. VFR conditions prevail. Nutter

&&

Preliminary point temps/pops...
gtf 32 44 32 44 / 10 10 20 20
ctb 29 42 29 42 / 10 10 20 20
hln 26 42 29 43 / 10 10 20 50
bzn 18 39 23 42 / 20 10 20 60
wey 15 31 21 31 / 20 20 50 100
dln 22 39 27 39 / 10 10 30 60
hvr 25 42 25 42 / 10 10 10 40
lwt 28 45 29 46 / 10 10 10 40

&&

Tfx watches/warnings/advisories...
High Wind Warning until 10 PM MST Saturday northern Rocky
Mountain front...southern Rocky Mountain front.

Winter Weather Advisory from midnight Friday night to 5 am MST
Sunday Beaverhead...central and southern Lewis And Clark...
Gallatin...Madison...northern Rocky Mountain front...southern
Rocky Mountain front.

High wind watch from late Friday night through Saturday evening
eastern Glacier.

&&

$$

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