Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 180925

Area Forecast Discussion
National Weather Service Great Falls MT
325 AM MDT Mon Sep 18 2017

An upper level trof of low pressure will approach the region on
Monday. As a result, expect increasing chances for lower elevation
rain and mountain snow by late Monday afternoon over the Rocky
Mountain front and across much of Southwest MT. A broad upper level
trof of low pressure will then reside over the region Tues through
Thursday...allowing for some passing rain or snow showers and below
normal temperatures to prevail across the region.



Today through Tuesday night...

The pattern becomes more active beginning today as a large upper
level moving onshore the PacNW and British Columbia will push a
leading cold front across the area. Expect rain showers to
consolidate into a solid, fast-moving band of rain with some
embedded squalls. Winds will increase especially behind the cold
front as the region remains under influence of the large-scale
upper level trough through Wednesday night, becoming strongest
along the Rocky Mountain Front and over the mountains. Enough
instability may exist Tuesday afternoon for a few lightning
strikes or isolated rumbles of thunder, but nothing severe is
expected. With low- to mid-level downslope flow persisting across
the plains, shower/thunderstorm chances will be highest over the
mountains of central and southwest Montana, where snow levels will
drop to as low as 5500-feet elevation. CC

Wednesday through Wednesday night...

Warm, moist air aloft will begin to move into southwest Montana
ahead of a strong disturbance and parent upper low Wednesday.
Meanwhile, at the surface, a cold front will drop south across the
region from Canada. This will set up a potentially prime
situation for widespread rain and mountain snow to develop
especially across parts of southwest and southern parts of central
Montana by late Wednesday into the overnight. This will bear
watching for the potential for moderate to heavy snowfall rates
over higher elevations south of Interstate 90 that could impact
travel. CC

Thursday through Monday...Active weather pattern expected to
continue through much of the long term period. Cut off low looks to
be somewhere over western ID by Thursday morning. As this low
progresses eastward areas of showers will fill in across the
region...initially across the west and south...then spreading
northward as an easterly upslope flow develops. Widespread shower
activity then looks to linger across much of the CWA for the rest of
Thursday...through Friday...then starting to diminish on Saturday.
Strong dynamics could evening bring some embedded thunder at times
during this time period...especially across the south. 700 mb temps
will be in the -4 to -6 C range which will be cold enough for snow
at about 6000 feet and higher...with accumulating snow likely above
7000 feet. Friday morning does see slightly cooler
temperatures...possibly lowering snow levels to near 5000 feet and
maybe lower to areas with heavier precipitation. Models currently
indicating a few heavy areas of rain and perhaps snow are possible
at times...mainly across the southwest and to the favored terrain in
an easterly upslope flow across central portions. This mentioned low
gets absorbed into a broadscale trough on Saturday...possibly
helping to diminish precipitation from west to east. By Sunday
generally dry conditions look possible with only a few isolated
mountain showers possible. Brief ridging also looks to keep dry
conditions into Monday. Cool conditions are expected for Thursday
and especially Friday...with highs only in the 40s and 50s and lows
in the 20s and 30s. A slow warming trend is possible for Saturday
through Monday...with perhaps highs near 60 by Monday. Anglin


Updated 0600Z.

VFR conditions will continue through much of tonight and into
Monday clouds increase ahead of an approaching cold
front. Widespread showers are then expected from west to east
Monday afternoon and evening. MVFR to brief IFR conditons are
possible with these showers. Conditions may then improve to MVFR
to perhaps some low VFR after the front passes Monday
night...although MVFR to IFR conditions may linger across southern
portions...including KEKS and KBZN. Westerly winds will also
increase with the passage of this front. Expect mountain
obscuration Monday afternoon through the remainder of the forecast
period...with the increased cloud cover. Anglin


GTF  63  40  55  38 /  60  60  20  20
CTB  59  36  55  35 /  40  30  10  10
HLN  61  36  53  34 /  60  60  40  40
BZN  64  36  52  32 /  50  80  50  40
WEY  60  28  45  22 /  60  80  70  50
DLN  59  34  49  30 /  50  60  30  20
HVR  70  41  62  37 /  40  60  10  10
LWT  66  39  54  33 /  30  40  20  20



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