Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 121726

Area Forecast Discussion
National Weather Service Great Falls MT
1026 AM MST Tue Dec 12 2017

...Updated Aviation Discussion...


Mainly just updated winds and wind gusts with the morning update,
but probably could have justified raising high temperatures today
2 to 3 degrees over much of the plains. Not as excited about the
wind highlights looking at the latest models but am concerned
about extreme fire weather danger for a brief period late this
morning into this afternoon. Have started messaging the fire
weather danger pretty hard this morning as a result, especially
when some locations have already reported RH values in the single
digits. Will hold off on issuing any fire weather highlights at
the moment, and will leave the wind highlights as-is but continue
to evaluate the need for any changes. CC


An upper level ridge of high pressure will be over the region
through Friday. However, expect windy conditions today over the
Plains of North Central MT while some patchy morning fog is possible
in the valleys of Southwest MT. Afternoon highs will be mild over
the north, with temperatures in the 50s, while 30s are expected over
Southwest MT. A slow change in the weather pattern arrives on
Friday, as the chances for rain or snow start to increase over the


Low humidity and strong winds are expected over the Northern
Plains today. However I will hold off on a highlight as afternoon
temperatures are expected to be overly mild. In either case, any
new fire starts out over the grass lands are going to be difficult
to contain today. Brusda


Updated 1726z.
VFR conditions will prevail over the region through tonight, though
increasing high clouds in association with a Chinook Arch cloud will
bring mainly BKN skies for much of the afternoon and possibly
extending into the evening. The two primary aviation impacts through
tonight will be the potential for patchy morning fog in the Helena
and West Yellowstone areas. The second problem is strong surface
winds through this evening over the Plains of North Central MT. The
winds should diminish after 03z Wed. After 12z Wed a fast-moving
system moves through west-central and southwest Montana bringing the
potential for a period of light snow and MVFR cigs to terminals from
KHLN to KBZN and KEKS.  CC/Brusda


/ISSUED 323 AM MST Tue Dec 12 2017/
Today...Strong winds and low humidity over the Northern Plains
will be the main concern. A very low jet max is progged to move
from west to east across the Highway 2 corridor from East Glacier
Park to Harlem today. With some minor mixing, strong winds are
expected today. The main threat will be sustained winds around
40 mph, with a few gusts in the 60 mph range. Thus a high wind
warning will be issued for a portion of the region. Afternoon
temperatures will be mild over the north with the mixing. Over
Southwest MT, repeat conditions, with a cold morning, some patchy
valley fog, and afternoon temperatures a few degrees below normal.

Tonight through Thursday...An upper level ridge of high pressure
will be just to our west. Wind speeds will be lower on Wed/Thu
over the north, thus it will not be as warm. Repeat conditions
will continue over the Southwest, but the fog should not be quite
as bad as we move into Thursday. There is a small chance for a
passing snow shower on Wed near Big Sky as well.

Friday and Saturday...A very slow change in the weather pattern is
expected to begin, as the upper level ridge of high pressure will
start to break down. Because of how strong the ridge is, it is
going to take a few systems to knock it down. Strong winds are
possible on Friday ahead of the precipitation. Expect a chance
for rain/snow especially by Friday night over much of the region.
Pops could be increased a bit over the next few days for Friday
night. As of now, the GFS progs about a 1 inch snowfall and the EC
progs a 2 to 3 inch snowfall.

Sunday...Both models prog a transition day, with breezy
southwesterly winds developing. This will warm temperatures a bit
over the north and allow only a small chance for a passing shower
over the Plains.

For Monday/Tuesday, the forecast models are differing when the
next storm will arrive. The EC is faster and has longer periods of
steady precipitation, while the GFS is slower, with the bulk of
the precip not arriving until next Wed. Thus kept a blend for
pops/temps but confidence is very low for the timing of this event
at this time. Brusda


GTF  56  30  45  28 /   0   0   0   0
CTB  54  26  45  25 /   0   0   0   0
HLN  35  14  35  14 /   0   0   0   0
BZN  35   8  33   8 /   0   0   0   0
WEY  27  -3  30  -3 /   0   0   0   0
DLN  39  15  38  15 /   0   0   0   0
HVR  53  20  44  20 /   0   0   0   0
LWT  52  25  42  25 /   0   0   0   0


High Wind Warning from noon today to midnight MST tonight

High Wind Warning until 6 PM MST this evening Eastern Glacier...
Liberty...Northern Rocky Mountain Front...Toole.


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