Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 221756
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1150 AM MDT Sat Apr 22 2017

Aviation Section Updated.

.UPDATE...

Skies have cleared across most of the forecast area, although
high cirrus are streaming over the upstream ridge. Low clouds
along and east of a line from near Havre to Lewistown will
continue to clear. Any remaining areas of patchy fog should erode
around 9am. Overall forecast remains in good shape, so issued
only minor updates to freshen with respect to observed trends. PN

&&

.AVIATION...
Updated 1750Z.
VFR conditions prevail today and tonight, except for MVFR ceilings
at KHVR/KLWT. These lower clouds will clear by around 19Z, with only
thin high cirrus over the region. Clouds increase early Sunday, with
possible showers and MVFR conditions across southwest MT. PN

.PREV DISCUSSION...
/ISSUED 615 AM MDT Sat Apr 22 2017/

Today (Saturday) through Monday...patchy morning fog is
possible across portions of North Central and Southwest Montana
through (8am-9am) due to abundant boundary layer moisture from
recent widespread rains, light winds, and dry air working in at the
mid to high levels. Shortwave ridging across the Intermountain West
will be quickly transitioning to the east across North Central and
Southwest Montana during the day today. This will set the stage for
the nicest day over the next 7 days. Some mid level clouds may
linger through the morning hours across far eastern portions of the
CWA, with sparse high clouds then filtering into western portions of
the CWA later in the day. However, bountiful amounts of sunshine
should be realized for the daytime hours generally south and west of
a Lewistown to Cut Bank line. Beneath these mostly to partly sunny
skies, high temperatures are expected to climb to near normal values
for April 22nd.

Clouds will then begin to increase in earnest tonight and into
Sunday morning as southwest flow develops aloft, ahead of the next
system moving onto the Pacific Northwest Coast. Upper level ridging
will begin to break down during the day on Sunday as shortwave
energy moves quickly across the Intermountain West. An area of low
pressure is then expected to develop along the lee of the Rockies
across Northern Montana/Southern Alberta late Sunday afternoon, with
a Pacific cold front then pushing southeast across the region Sunday
evening and into the morning hours on Monday. Rain showers, mountain
snow, and even a few isolated thunderstorms (across Southwest
Montana) will be possible across North Central and Southwest Montana
during the late morning and into the afternoon ahead of the
approaching system on Sunday. Following the passage of the cold
front, rain will change over to snow as low as 4500 feet Sunday
night/Monday morning. Accumulating snow will be possible above 4,500
feet Sunday night and into Monday morning, however, accumulations
appear light for most elevations with the exception of the highest
peaks. 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. - Moldan

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.
Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  60  40  53  36 /   0  10  60  20
CTB  56  38  55  35 /   0  10  20  20
HLN  63  42  56  38 /   0  10  50  30
BZN  61  38  56  36 /   0  10  50  50
WEY  49  29  49  30 /   0  10  60  60
DLN  58  38  55  36 /   0  10  50  50
HVR  57  39  54  36 /   0  10  50  30
LWT  59  39  55  35 /   0  10  50  40

&&

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

$$

weather.gov/greatfalls



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