Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 240455
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1055 PM MDT Tue May 23 2017

Aviation Section Updated

.UPDATE...

No significant changes to the forecast this evening. Main change
was to increase mention of clouds this evening due to thinner
mid level cloudiness from a Chinook arch. Wind forecast appears to
be on track, so made no changes at this time. Latest short range
models indicate slightly warmer overnight lows tonight than
previously forecast (only a degree or two warmer, though) which
seems reasonable due to the expected increase of downsloping
winds over the plains.
Coulston

&&

.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.

&&

.AVIATION...
Updated 0455Z.

An anomalous upper level low and associated low/mid level jet will
encroach on the area overnight with increasing winds at the SFC. The
wind will first increase along the Rocky Mtn Front and adjacent
plains overnight, then the wind will increase elsewhere on
Wednesday, especially in the wake of a strong, but dry, cold front
moving through. Widespread gusts of 35-55kt are likely through
Wednesday evening. As the wind shifts around to the NW Wednesday
evening, low level moisture will increase, leading to lower CIGS and
scattered SHRA, but mainly from KCTB to KHVR. Elsewhere, moisture
will gradually increase as well, but beyond the current TAF cycle.
Martin

&&

.PREV DISCUSSION...
/ISSUED 606 PM MDT Tue May 23 2017/

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  57  61  42  59 /   0  10  40  30
CTB  50  56  41  58 /   0  10  50  20
HLN  52  65  44  61 /   0   0  30  20
BZN  49  67  39  57 /   0  20  20  30
WEY  41  63  29  50 /   0  10  10  30
DLN  49  64  36  56 /   0  10  10  20
HVR  56  66  45  61 /   0   0  40  30
LWT  52  66  40  56 /  10  10  30  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from 6 AM Wednesday to midnight MDT Wednesday
night Blaine...Cascade...Central and Southern Lewis and Clark...
Chouteau...Eastern Glacier...Eastern Pondera...Eastern Teton...
Fergus...Hill...Judith Basin...Liberty...Toole.

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

&&

$$

weather.gov/greatfalls


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