Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 231954
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
154 PM MDT Tue May 23 2017

.SYNOPSIS...

High pressure will move off to the east tonight for increasing
clouds and generally mild overnight temperatures. Strong winds
develop late tonight and spread east across much of north central
Montana on Wednesday as a strong low pressure system tracks into
Alberta. Damaging winds of 50 mph or more are possible across
portions of North central MT Wednesday into Wednesday evening.
Temperatures cool on Wednesday as well with dry conditions
prevailing. Memorial Day weekend will start out cool with
temperatures returning to near normal. Some widely scattered
shower activity is also possible at times.

&&

.DISCUSSION...

Tonight through Thursday...Vigorous upper level low currently moving
into the central BC coast will track ESE tonight, emerging in
southern AB Wednesday morning. At the surface, low pressure deepens
across southern AB late tonight through Wednesday morning with a
strong but mainly dry cold front sweeping east across the forecast
area Wednesday morning as the surface low moves to a position along
the AB/SK border with trough axis trailing SW across central/SW MT.
Winds aloft increase significantly late tonight across NW portions
of the forecast area with strong winds likely developing along the
immediate east slopes of the Rockies after midnight. Gusty west
winds will surge east with the frontal passage Wednesday morning,
bringing the potential for wind gusts in the 40-50kt range to much
of N-central MT. Winds aloft remain fairly strong through Wednesday
afternoon and evening, with daytime heating/mixing keeping very
windy conditions going through Wednesday afternoon. Winds aloft veer
to the NW and N Wednesday night as the low moves east into SK with
models indicating a secondary surge of stronger NW/N winds moving
down behind the low into N-central MT. This should bring another
round of strong wind/gusts Wednesday evening, this time affecting
areas further east including Judith Basin and Fergus counties.
Confidence in 50kt winds gusts with this event is highest for areas
along the Rocky Mtn Front and somewhat lower for areas to the south
and east. However this is an anomalous wind event for this late in
the spring season with 700 MB wind speeds progged to exceed 4
standard deviations from climatology. Given that, and potential for
impacts with somewhat lower winds speeds due to leaves on most
deciduous trees and increased trailer pulling traffic ahead of the
holiday weekend, have expanded the warning to cover all of N-central
MT. Moisture wrapping around the upper low spreads south and east
from AB Wednesday night and Thursday with best chance for measurable
precipitation over the higher terrain of north-central MT as well
along the Canadian border. Hoenisch

Thursday night through Tuesday...Tightly wound sfc low across
Canada will slowly pull out of the region Thursday night with
diminishing winds, but still breezy at times, expected. A
broadscale trough extending from the upper low in Canada will then
be draped across much of the CWA for Friday. The result will be
continued cooler temperatures with some scattered shower activity.
The best chances for this shower activity will be along and west
of a line from Cut Bank to Great Falls to Billings. Weak
instability could also bring a few thunderstorms, however, they
will be isolated and below severe criteria. We then find ourselves
between a ridge to our west and the large upper low to our east
in central Canada for Saturday. The result will be weakly moist
northerly flow with slightly warming temps. More widely scattered
shower activity is again possible on Saturday, with isolated weak
thunderstorms. The high to our west encroaches a little bit more
each day for the remainder of Memorial Day Weekend, bringing
warming temperatures and only isolated shower and thunderstorm
activity. This ridge then struggles to stay established on
Tuesday, with weak disturbances in nw flow possibly bringing a few
more scattered shower and isolated thunderstorm chances. As
hinted, each day in the extended will be warmer than the previous.
By Sunday into next week 70s could return to the area. Some
models are even hinting low 80s are possible during this time
frame, especially across the central and northern plains. Winds
will be nothing like Wednesday and Thursday, but may be breezy at
times through Sunday especially across the north and east. Anglin

&&

.AVIATION...
Updated 1700Z.

High pressure ridge aloft shifts east across the Northern Rockies
and MT for dry NW flow aloft today, becoming westerly and
increasing tonight. VFR conditions prevail with increasing high
cloud-cover later today and tonight. Vigorous low pressure system at
the surface and aloft moves across southern BC and AB late tonight
through Wednesday with strong west winds developing late tonight
along the Rocky Mtn Front, spreading east across N-central MT
Wednesday morning. Sustained west winds 30-40kts are likely across
most N-central MT terminals Wednesday with some gusts over 50kts
along the east slopes of the Rockies and along the Canadian border.
Gusty winds in excess of 25-35 kts also possible at SW MT terminals
Wednesday with widespread Mtn wave turbulence all areas. Hoenisch

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  56  60  42  59 /   0  10  40  30
CTB  49  55  41  58 /   0  10  50  20
HLN  53  64  44  61 /   0   0  30  20
BZN  47  66  39  57 /   0  20  20  30
WEY  37  69  29  50 /   0  10  10  30
DLN  49  63  36  56 /   0  10  10  20
HVR  55  65  45  61 /   0   0  40  30
LWT  51  65  40  56 /  10  10  30  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from 6 AM Wednesday to midnight MDT Wednesday
night Eastern Glacier...Eastern Pondera...Eastern Teton...
Liberty...Toole.

High Wind Warning from midnight tonight to midnight MDT
Wednesday night Northern Rocky Mountain Front...Southern Rocky
Mountain Front.

High Wind Warning from 6 AM Wednesday to midnight MDT Wednesday
night Blaine...Cascade...Central and Southern Lewis and Clark...
Chouteau...Fergus...Hill...Judith Basin.

&&

$$

weather.gov/greatfalls



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