Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 172317 AAA
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
518 PM MDT Sun Sep 17 2017

...update aviation
.SYNOPSIS...
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.

&&

.DISCUSSION...
Tonight through Tuesday night...Quiet weather tonight will give
way to slightly more active weather Monday through Tuesday. An
upper level disturbance will approach the region Monday
afternoon/evening...producing showers along the divide by Midday,
and then spreading them through Central/Southwest MT during the
afternoon and evening hours. Some locations could get around 0.30
inches of precipitation. Isolated thunderstorms are possible
mainly during the late afternoon over the far eastern sections of
the region. The precip moves northeastward Monday night...possibly
changing to snow for elevations above 5500 feet or so. An inch/or
two is possible in the mountains. Scattered showers continue over
much of Southwest MT and the Rocky Mountain Front on Tue/Tue night
as a deep upper level trof develops over the region. Areas along
and north of Highway 2...from Cut Bank to Harlem will likely see
little/no precipitation on Tue/Tue night. Brusda

Wednesday through Sunday...Latest model trends remain in good
agreement in regards to a emebedded shortwave trough rotating
around a dominant cyclonic flow across the Pac NW. At the surface,
a sub- 1000mb low will likely make its way on shore the Pacific
Coastline, and quickly eject eastwards across WA/OR/ID and bring
with it widespread rain, and perhaps a few thunderstorms to
eastern and central MT by early Wednesday. Exact timing on the
arrival remains in question, however confidence is increasing that
another widespread rain event will spread across the CWA through
the day on Wednesday and into Wednesday night. In regards to QPF,
models are in slight disagreement with precip totals ranging
between 0.25 to possibly 0.75 inches or more, especially across
central and southwestern areas. By Thursday and Friday, we will
continue to see mostly cloudy, wet and cool conditions with off
and on light rain showers as we remain in control of the slow
moving upper-level low/longwave trough. Temperatures Wednesday
through Friday will be cool with afternoon highs averaging 10 to
15 degrees below normal. As we get into next weekend, the longwave
trough will finally drift east and de-amplify as ridging builds
across the NE Pac. This will allow for a progressive NW flow aloft
to set up, keeping the area cool. While daily shower chances will
remain mostly scattered to isolated at most, a few small
disturbances along the flow from SW Canada may produce some
periods of light rain. The pattern following next weekend
continues to show confidence between the EPS and GEFS with
persistent low height anomalies across the NW US. This supports
the potential for continued wet and cool conditions through next
week with still no sign of returning warmth or heat in the long
range. KLG

&&

.AVIATION...
Updated 2318Z.
VFR conditions will continue over the region this afternoon through
tonight...with just some passing mid/high level cloudiness. On
Monday...expect scattered showers to develop along the divide and
across Southwest MT by 18Z. This precipitation will start to spread
into Central MT during the afternoon hours on Monday. Some IFR
conditions are possible by 18Z Monday...especially in the
mountains/passes. Winds will be gusty in the afternoon as well. db

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  48  61  39  56 /   0  20  60  20
CTB  45  60  36  54 /  10  20  10  10
HLN  45  60  36  54 /   0  70  70  40
BZN  41  65  37  51 /   0  10  80  40
WEY  33  55  31  41 /   0  20  80  70
DLN  42  59  33  47 /   0  30  60  40
HVR  45  66  41  62 /   0  10  60  10
LWT  45  66  39  54 /   0  10  50  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

weather.gov/greatfalls


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