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Area forecast discussion
National Weather Service Great Falls Montana
1050 PM MDT Sat Apr 22 2017

..updated aviation section...


Continued to up pops for the late tonight through Sunday night
period as models are continuing to come into good agreement with
timing and progression of a weather front through our region. Rain
should transition to a more showery regime in the afternoon and
evening as stability decreases, particularly over central and
southwestern Montana, where a thunderstorm or two can not be ruled
out. Cassell


updated 0450z.

A disturbance in the moist southwest flow aloft will spread low/mid
clouds over the area through 15z, for widespread low VFR/MVFR
ceilings and mountain obscuration in Rain/Mountain snow. Brief IFR
conditions are possible in heavier showers. A weak frontal boundary
will move east of The Rockies after 17z, shifting surface winds more
westerly there. Conditions will gradually improve from the west
between 20z and 06z as the disturbance exits the area.


Previous discussion...
/issued 520 PM MDT Sat Apr 22 2017/

Tonight through Monday...water vapor imagery reveals a narrow dry
slot crossing western Montana this afternoon, following along and
just behind the axis of a collapsing upper level ridge. This will
result in a brief thinning of high cloud cover, providing a mostly
sunny afternoon. The next shortwave trough is located upstream
over northern California. High clouds in advance of this wave are
already reaching southwest Montana. These clouds will continue to
spread over the area tonight, with scattered rain and mountain
snow showers likely early Sunday over southwest Montana.
Precipitation then spreads north and east across central Montana
during the day Sunday. Weak instability will support a few
thundershowers. The shortwave exits to the east Sunday night, but
westerly flow will continue to support isolated to scattered
showers over mountain areas. Snow levels on Sunday will be as high
as about 8000 feet, then drop to around 5000 feet by early
Monday. Rain and snow showers will then be possible for the day on
Monday, as another fast moving upper level disturbance treks
eastward within the then zonal/troughy flow aloft. Pn

Monday night through Saturday...a moist westerly flow aloft is
expected to reside over the region for all of next week. As a result
periods of rain/snow are expected across the entire region through
the entire extended period. For Tue/Wed and Friday the National
blend is quite a bit higher with pops, and that looks good. Thus
pops have been raised those days. Otherwise, with cold air aloft,
combined with daytime heating and weak upper level disturbances
moving through, scattered showers are possible on the other days.
None of the weather systems look to be very strong at this time, but
precipitation amounts of 0.20 to 0.40 inches will be possible on the
wetter days. There will continue to be the chance for snow, mostly
in the mountains for elevations above 5500 feet, but snow levels
could lower to around 4500 feet at times, especially during the
overnight hours. Snow accumulations of 1 to 2 inches look possible
each day in the mountains. However impacts to roadways looks to be
on the low side, as melting will occur, but slippery spots/stretches
are still possible. In terms of temperatures, afternoon highs will
be fairly consistent from day to day, with highs in the low/mid 50s,
which is about 4 to 8 degrees below normal for this time of year.


Preliminary point temps/pops...
gtf 41 53 36 57 / 30 80 50 30
ctb 39 56 35 53 / 20 30 20 50
hln 43 55 38 56 / 40 90 30 40
bzn 39 56 36 55 / 40 80 60 50
wey 31 48 29 44 / 30 60 60 60
dln 40 55 36 53 / 70 90 70 40
hvr 41 53 36 58 / 30 60 40 40
lwt 40 54 35 54 / 20 90 60 40


Tfx watches/warnings/advisories...

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