Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 311727
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1127 AM MDT WED AUG 31 2016

UPDATED AVIATION

.UPDATE...Somewhat unstable southwest flow aloft will prevail
across the forecast area today and tonight. Forecast for isolated
to scattered showers and thunderstorms continues to look good.
However, have updated PoPs/weather with most recent short term
consensus tools which keep shower activity mainly over the western
mountains through 6 PM MDT so isolated PoPs over the plains and at
most forecast points have been dropped until the evening portion
of the forecast. Have also used consensus tools to update high
temperatures today and overnight lows tonight. Finally, many
locations across my CWA are reporting reduced visibilities due to
wildfire smoke so have added areas of smoke today, tonight and
tomorrow across the entire forecast area. mpj

&&

.AVIATION...
UPDATED 1727Z.

VFR expected through 18Z/Thu. Southwesterly flow aloft
will persist as the axis of a mid to upper-level ridge shifts from
eastern MT and SK to the Dakotas and MB by 18Z/Thu. A weather
disturbance embedded within this flow should move northeastward
from central ID to southern AB/SK by 06Z/Thu. Thus, -SHRA/-TSRA
should form over the higher terrain between 19Z and 22Z/Wed and then
move northeastward. This activity should exit the area between 06Z
and 09Z/Thu. Erratic wind gusts of 30-45 knots are possible with any
thunderstorm. Patchy smoke will likely persist throughout the
period, especially at KHLN, but VIS should remain within the VFR
range. Jaszka

&&

.FIRE WEATHER...
Fire danger remains elevated across central MT today as dry
conditions (aftn humidities in the teens again) continue under the
high pressure ridge parked over the eastern two-thirds of the
state. Surface low pressure forming over the central plains will
generate locally breezy conditions this aftn, but speeds and
coverage of these slightly stronger winds look to remain below
criteria for any fire weather headlines, though some near-
critical fire weather conditions are possible for short periods
this aftn. There is additional concern with the possibility for
gusty outflow winds that may develop with this aftn/eve`s
thunderstorms. Several forecast soundings show textbook
"inverted-V" temperature/moisture profiles that could lead to
outflow winds of 35-45 mph. Those would be sufficient to promote
rapid fire growth in lighter fuels on any existing or new fires.
Waranauskas

&&

.PREV DISCUSSION...
/ISSUED 525 AM MDT WED AUG 31 2016/
Today through Friday Evening...Persistent high pressure ridge
centered over eastern MT brings another day of mostly dry conditions
and unseasonably warm temperatures (upper 80s to mid 90s, with a few
upper 90s) to our region today.  Current analysis shows one weak
trof just west of the ridge axis steadily exiting from our area into
Alb/Sask, with a second trof and associated moisture lifting
northeastward from NV into southwest ID.  The second trof arrives in
the southwest counties by late aftn, and should generate broader
coverage of thunderstorms through this eve, but most locations will
only have 20-25 percent of getting any rainfall from these storms.
Continued dry conditions in the lowest portion of the atmosphere
will also contribute to evaporating some precip that does form as
well as enhancing outflow winds as the storms collapse.  See Fire
Weather section below for further discussion on the dry conditions.

Forecast models remain consistent on the ridge drifting east into
the Dakotas on Thurs in response to the large low pressure system
beginning to turn inland along the BC/WA coast. This system will
bring a major change in conditions on Fri and through the weekend.
Minor shortwave ahead of the main trof will combine with a mix of
Pacific and monsoonal moisture to produce scattered thunderstorms
from the Little/Big Belt Mtns southward on Thurs aftn/eve. As the
Pacific system tracks eastward, it will push a sharp cold front
east of the Continental Divide by late Fri morning with the front
sweeping through our region during Fri aftn. Scattered
thunderstorms are expected along/ahead of the front, mainly over
the Rocky Mtn Front and Hiline/central counties. Not expecting
much rainfall(around a tenth of an inch or less) with any rounds
of thunder-storms. Temps cool significantly back to the mid 70s
(and low 80s over Blaine/Fergus counties) on Fri.
Waranauskas

Friday Night through Wednesday...Model solutions have attained a
reasonable consensus regarding the initial advance of seasonally
colder air moving into the region through the Labor Day weekend. As
the surface front moves away to the east Friday night, the mid-level
center of circulation remains to our north and deepens over Alberta.
Hence, precipitation associated with the large scale ascent remains
concentrated over the Canadian Rockies. A brisk westerly downslope
flow keeps our forecast area cool, windy and generally dry on
Saturday except for possible rain showers over the northern Rocky
Mountains. A secondary wave drops through eastern Washington on
Sunday, tracking through southwest MT Sunday night. Model solutions
begin to diverge at this time, but still have enough confidence to
add near-likely precipitation in the forecast. Snow levels Monday
morning drop below 7000 feet over the Northern Rockies, so
backcountry travelers should be aware that light to moderate snow
accumulations are possible at mid to higher mountain levels.  High
temperatures at lower elevations Sunday and Monday will struggle to
reach 60F, while overnight frost becomes possible in the higher
southwest valleys. The pattern transitions Monday night to a more
zonal flow with a series of weak embedded disturbance. Hence, the
forecast maintains slight chances for showers and isolated
thunderstorms into next week. Temperatures gradually rebound, yet
still remain below average through the period. PN

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  94  59  88  53 /  10  20  10  20
CTB  88  54  82  50 /  10  20  10  20
HLN  91  58  88  55 /  10  20  20  20
BZN  92  53  88  51 /  10  10  20  20
WEY  79  46  76  45 /  10  20  20  10
DLN  88  51  85  49 /  10  20  30  20
HVR  96  60  90  55 /  10  20  10  20
LWT  94  59  89  56 /  10  20  20  30

&&

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

$$

weather.gov/greatfalls



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