Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 251735
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1134 AM MDT THU AUG 25 2016

...Aviation Section Updated...

.DISCUSSION...

Today...A weak disturbance in the northwest flow aloft is
approaching the Canadian border. High clouds will move into the
central zones later this morning but most precipitation will occur
over night. Update to zones not planned...current forecast on track.
Zelzer

&&

.AVIATION...
UPDATED 1734Z.

An upper level shortwave noted on satellite imagery over southern
Alberta will drop south into Montana this evening, then move off to
the SE by Friday morning. Moisture associated with the s/w will push
into the forecast area later today and tonight and will be
accompanied by increasing low/mid level clouds as well as some light
SHRA, mainly across central Montana. For now, kept all sites at VFR
CIGS, but MVFR CIGS and mtn obscurations will be possible as the low
level moisture / SHRA move in. Of note, there may be enough
instability for a TSRA late this afternoon through early this
evening, mainly vicinity KCTB. Confidence was too low to include TS
in the TAF there for now, though. SHRA will gradually begin to taper
off from west to east late in the TAF cycle. Martin

&&

.PREV DISCUSSION...
/ISSUED 537 AM MDT THU AUG 25 2016/

Today through Saturday...This morning through most of the daytime
hours we will find ourselves caught in between weather systems.
Limited precipitation has come to an end across the CWA during the
overnight hours...however...some lingering moisture will continue
a few mid level clouds through this morning...and redevelop a few
in the afternoon hours. Late this afternoon through tonight...A
weak shortwave and its associated cold front will push south out
of Canada across the region. This will provide for isolated
showers. Widely scattered thunderstorms are also possible across
the area...although shear and instability will be on the low
side...limiting any chances for strong storms. The best chances
will come across the Rocky Mountain Front...the Hi- Line...and
possibly as far south as Great Fall to Lewistown. Showers will be
light with little qpf expected. Limited shower activity could
then linger into Friday as the system exits the region. Limited
but widespread instability could even bring a few thunderstorms
Friday afternoon. Increasing shear on Friday afternoon perhaps
could provide for an isolated stronger storm...however...no severe
weather is expected at this time as cape values are low.
Precipitation chances diminish pretty quickly Friday evening
through Friday night. An upper level low in far northern Alberta
will then swing a weak disturbance across the area for Saturday.
It appears this disturbance will bring with some moisture...the
downfall with this feature is the increasing cross mountain
flow...causing breezy and dry downsloping winds. Added some
isolated showers in the mountains...however...chances for anything
in the dry air across the plains are too low to introduce slight
pops. Instead just placed some increased cloud cover with this
feature for the remainder of the area. Temps will remain below
season norms with today`s front. Below average temps will
continue for Friday...with warming back into the 80s (roughly
average for this time of year) expected for Saturday. With
continue cool temps and some lingering/limitedly increasing
moisture...fire weather concerns are low for today and
Friday...except across far sw MT where RH values will continue to
be low. Saturday may see elevated fire danger with dry air and
breezy condtions across the region. Anglin

Saturday night through Thursday...Medium range models continue to
show that the upper level pattern will be dominated by a western
Canada trough for much of next week. This remains similar to earlier
forecast runs but the most recent model runs appear to be slightly
weaker with this feature and have backed off a bit on possible
shower coverage. It is also worth noting that the ECMWF appears to
have trended toward the GFS solution that keeps bulk of the energy
associated with the upper trough in a closed low over Southeast
Alaska. As noted yesterday, both models keep Montana beneath
southwest flow aloft through the period. Tonight`s model runs
suggest that shortwave energy ejecting from the West Coast trough
will likely move through Canada rather than Montana which would help
to explain the slightly lower PoPs that solutions are presenting
tonight. Have once again made only minor changes to the going
forecast with early to mid-week PoPs being reduced somewhat and
temperatures perhaps a degree or two warmer. mpj

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  69  45  70  50 /  10  20  20  10
CTB  68  45  69  50 /  30  30  20  10
HLN  70  47  73  50 /  10  20  20  10
BZN  71  42  73  43 /  10  20  10  10
WEY  65  34  65  37 /  10  20  20  10
DLN  70  41  73  44 /  10  10  10   0
HVR  71  49  71  49 /  20  30  30  10
LWT  67  46  67  48 /  10  20  20  10

&&

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

$$

weather.gov/greatfalls



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