Area Forecast Discussion

FXUS65 KTFX 112100
Area Forecast Discussion
National Weather Service Great Falls MT
200 PM MST Mon Dec 11 2017
Stagnant upper level weather pattern finally begins to change late
tonight into Tuesday as a strong disturbance sweeps across 
Alberta and Saskatchewan. Windy to very windy conditions with 
above normal temperatures are expected over the plains, but the 
valleys of Southwest Montana will remain cool with areas of late
night and early morning freezing fog. A change in the weather 
pattern is expected late this week, with a better chance for rain
and snow showers developing.
Today through Tuesday Night...The stagnant pattern of the last
week or so finally begins breaking down as a disturbance rides
over the top of the ridge tonight, then moves southeastward
through Alberta on Tuesday. Main impact of this disturbance is
expected to be lowering surface pressure in Alberta/Saskatchewan
with downslope pressure gradients along the east slopes of the
Rockies becoming stronger and tighter. Additionally, mid- and
upper-level winds will increase substantially with daytime heating
helping some of these stronger winds to mix to the surface. As a
result, am expecting strong and gusty winds to develop along the
Northern Rocky Mountain Front late tonight/early Tuesday, with
strong winds spreading eastward along the Hi-Line and into my
eastern zones during the day on Tuesday. Have therefore opted to 
issue a High Wind Watch for these areas beginning at 6 AM MST 
Tuesday and continuing into the evening hours. Forecast high
temperatures on Tuesday will once again rise into the 50s across
North Central Montana. mpj
Wednesday...A weak upper level disturbance will move through
Southwest MT, with a light snow shower possible around Big Sky.
Otherwise persistence continues across the region for
Thursday/Friday...The start of a gradual weather change to more
December like conditions should begin. A stronger upper level
disturbance will move into the Northern Rockies by late Friday,
producing some rain/snow showers over the region. The
precipitation looks to be most widespread Friday night. Afternoon
temperatures will still average about 10 degrees above normal for 
most areas though. There is the potential for some stronger winds 
during this period, especially along the front range of the Rockies.
For Saturday through Monday...Confidence in the forecast gets
lower each day through the period...becoming quite low by Monday.
Expect a few passing showers on Saturday, with forecast models 
differing for Sun/Mon. The EC wants to bring in a fairly good size
weather system for late Sunday into Monday. This would result in 
colder temperatures and a good chance for accumulating snow. The 
GFS/NBM is drier and not as aggressive with the colder air. For 
now I leaned towards the GFS/NBM solution, but significant changes
in the forecast are possible by early next week. Brusda
Updated 1720z.
VFR conditions will prevail across much of the region through the
period. The exception will be the valleys of Southwest MT, mainly
around Helena/West Yellowstone where some patchy freezing fog is 
possible during the early morning hours. Surface winds will be 
generally light today but are expected to increase significantly 
after 15Z Tuesday. mpj
GTF  32  55  32  46 /   0   0   0  10 
CTB  27  54  28  45 /   0   0   0   0 
HLN  18  35  23  39 /   0   0   0  10 
BZN  13  33  18  37 /   0   0   0  10 
WEY  -5  26   4  32 /   0   0   0  10 
DLN  17  37  20  41 /   0   0   0  10 
HVR  25  55  26  45 /   0   0   0  10 
LWT  30  55  29  43 /   0   0   0   0 
High Wind Watch from Tuesday morning through Tuesday evening 
Blaine...Chouteau...Eastern Glacier...Eastern Pondera...Fergus...
Hill...Liberty...Northern Rocky Mountain Front...Toole.