Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 272341

Area Forecast Discussion
National Weather Service Great Falls MT
540 PM MDT THU OCT 27 2016

Aviation Section Updated


Tonight through Saturday...A mid- to upper-level high pressure ridge
will persist over much of the CWA through the period. However,a
weather disturbance over northern AB at time of writing will move
southeastward, while another weather disturbance nearing the Pac NW
and southern BC will continue moving northeastward. These two
disturbances will merge over the AB/SK plains Friday morning before
reaching western ON early Saturday. Accordingly, a surface cool
front is expected to move southward into the Hi-Line early Friday
morning and then reach Southwest Montana by early Friday afternoon,
before dissipating over that part of the CWA soon afterward. Yet
another weather disturbance centered well west-southwest of CA`s
Channel Islands, near 130W, at time of writing is expected to
undercut the aforementioned ridge as it moves northeastward to
eastern ID by early Saturday and then moves east-southeastward to
near IA by early Sunday.

The aforementioned weather pattern will allow skies will be partly
to mostly cloudy over the CWA. As the surface cool front moves
southward, it should trigger only a few light showers due to limited
low-level moisture ahead of the front. In addition, a few showers
should be expected along the Rocky Mountain Front, including Glacier
Park. Finally, periods of precipitation are expected in Southwest
Montana, especially Friday morning through Saturday morning, due to
the aforementioned weather disturbance undercutting the mid-to upper-
level high pressure ridge. Per latest model data, the best potential
for precipitation in our southwest counties should be south of a
Helena to Lewistown line. Total liquid precipitation amounts during
the period will range from no more than a few hundredths of an inch
along and north of the Helena to Lewistown line to near a tenth to
three quarters of an inch south of that line. The greatest
precipitation amounts will likely be realized in the Southwest
Montana mountains. Snow levels should average near 7000 feet MSL in
North-Central Montana and near 8500 feet MSL in Southwest Montana.
Therefore, mountain passes should experience very little, if any
accumulating snow.

Many places will have lows in the 40`s tonight and then highs in the
low to mid 50`s Friday. Lows will then reach the 30`s in many
locations Friday night. On Saturday, highs will mainly reach the
upper 40`s to mid 50`s. These lows will be about 10 to 15 degrees
above average, while highs will be near-normal for late October.

Saturday Night through Thursday...Clouds increase once again from
the west Saturday night as a shortwave ridge axis moves downstream.
Weak warm advection will lift areas of rain into the Northern
Rockies early Sunday. Precipitation continues but shifts further
south and spreads across southwest Montana on Sunday as a jet streak
intensifies in a moist southwest flow aloft. The center of a
significant Pacific trough moves inland across the central west
coast Sunday night, and continues across the central Rockies on
Monday. Periods of rain will accompany the passage of this system,
continuing to affect mainly central and southwest Montana. Snow
levels lower to around 5500 feet over the Northern Rockies, to
around 7000 feet for Southwest MT by Monday evening with snow
possible on area passes.

Monday evening...Halloween: Areas of rain early Monday afternoon
should taper and move east on Monday evening. However, showers may
linger in some areas. Temperatures on Monday evening should be in
the lower to mid 40s for most plains and valley locations.

Tuesday through Thursday...Model solutions diverge through this
period but generally indicate a drier split flow pattern over the
northern Rockies. PN


Updated 2340Z.
Widespread mid/high level clouds will reside over the region through
the period, with some mountains/peaks obscured at times. Expect
showers over the Rocky Mountain Front, while scattered showers
increase over Southwest MT around 12z Fri. Downslope winds should
limit chances for rain over the Plains of North Central MT through
the period. Brusda


GTF  70  41  54  37 /  10  20  10  10
CTB  63  34  50  32 /  10  20  10  10
HLN  69  38  55  36 /  10  20  20  20
BZN  70  42  56  38 /   0  20  40  60
WEY  58  34  49  34 /  10  50  70  80
DLN  69  40  55  38 /   0  30  40  60
HVR  67  38  51  33 /  10  20  10  10
LWT  69  40  53  36 /   0  10  20  30




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