Area Forecast Discussion
Issued by NWS Great Falls, MT

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136
FXUS65 KTFX 302131
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
331 PM MDT SAT JUL 30 2016

.DISCUSSION...

SATURDAY AFTERNOON THROUGH MONDAY...A shortwave low pressure
trough will bring increasing westerly winds to North Central and
Southwest Montana through Sunday evening, but less breezy
conditions are expected for Monday. Overall, though, skies will
remain mostly clear, except near thunderstorms. Very isolated
thunderstorms have developed this afternoon. Relatively speaking,
the most unstable airmass (CAPE 1000-2000 J/kg) is along and east
of an inverted surface trough currently centered over a Dillon to
Havre line. This is where isolated thunderstorms will linger into
this evening. Wind shear is moderate at best, so thunderstorms
with strong wind gusts, brief heavy rain, and small hail are
possible. Loss of daytime heating will help stabilize the
atmosphere overnight. A Canadian cold front will then move
southeast to the Hi-Line by sunrise, then through the remainder of
North Central Montana throughout the day. A few showers and
thunderstorms may develop along the Hi-Line in the wake of the
front and over the mountains of Southwest Montana during the
afternoon along and ahead of the front. However, these storms are
less likely to become strong. The main issue for Sunday will be
the increasing west to northwest winds, as conditions will
generally be dry (please check FIRE WEATHER discussion for
details). Wind gusts could reach 30 mph at times during the
afternoon, which may be amplified near any thunderstorms. As high
pressure aloft builds into the area overnight into Monday, quieter
weather with less wind is expected. Even with the weak cold
frontal passage, temperatures will only fall to near normal
levels.  Coulston

MONDAY NIGHT THROUGH SATURDAY...Upper level ridging briefly
shifts east across the region Monday night through early Tuesday
with temperatures warming back to somewhat above average levels
again by Tuesday afternoon. A compact upper level low moves
inland along the WA/BC border Tuesday and continues east along
the MT/AB border Tuesday night. Diffluent SW flow aloft and
incoming upper level jet maximum ahead of the low will focus
greatest large scale lift across N-Central MT Tuesday afternoon
and evening with a cold front also looking to shift east across
the region during the late afternoon period. This could create a
favorable set-up for potentially severe convection Tuesday
afternoon/evening if enough moisture can return, which is
appearing more likely with an inverted surface trough setting up
across S-central/central MT Tuesday and E/NE low level flow ahead
of the front across the N-central MT plains. Drier and cooler air
moves in behind the front late Tuesday night through Wednesday as
the upper low tracks east along the MT/SK border with just a
small chance for showers along the Canadian border. Thursday
through Saturday period looks to gradually warm as heights build
around an upper level ridge centered over the central CONUS with
weak troughing oriented along the West Coast. Hoenisch

&&

.AVIATION...
Updated 1720Z.

VFR will likely prevail through 18Z/Sun. However, a few showers
and TSRA should develop over the mountains after 18Z/Sat before
dissipating between 00Z and 03Z/Sun. This activity may briefly
impact KHVR and KLWT between 19Z and 22Z/Sat. Brief MVFR and
erratic wind gusts up to 40 knots may accompany TSRA. Flow aloft
should back from westerly to west-southwesterly and strengthen
slightly by 06Z/Sun as a weather disturbance moves southeastward
from central British Columbia toward Northwestern Montana. Jaszka

&&

.FIRE WEATHER...

Warm, dry, and breezy conditions will continue to bring fire
weather concerns to much of North Central and Southwest Montana
through Sunday. Though conditions are very warm and dry this
afternoon (Saturday), gusty westerly surface winds have just
developed. Calculated fire danger (taking into consideration fuel
moisture) is still expected to only be in the high category. These
conditions are only marginal at best for potential fire weather
highlights, so will hold off on anything for now. A Canadian cold
front will then move across North Central Montana on Sunday.
Though temperatures will not be quite as warm as today, afternoon
humidity will fall into the 10 to 20 percent range once again.
Winds will also be a bit stronger out of the west to northwest,
possibly gusting up to 30 mph. Both of these factors again provide
only marginal conditions for a fire weather watch/warning. If the
forecast fire danger for portions of the area come in as very high
this afternoon, highlights may be needed. Will continue to monitor
the situation.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  57  88  50  86 /   0   0   0   0
CTB  54  78  48  80 /  10  10  10   0
HLN  62  90  53  89 /  10   0   0   0
BZN  54  90  47  88 /  10   0  10   0
WEY  48  80  41  79 /  20  10  10   0
DLN  53  86  46  85 /  10   0  10   0
HVR  59  86  52  84 /  10  10   0   0
LWT  59  86  51  83 /  10  10  10   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
&&

$$

weather.gov/greatfalls



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