Area Forecast Discussion
Issued by NWS Great Falls, MT

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902
FXUS65 KTFX 231654
AFDTFX

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

Updated Aviation Discussion

.UPDATE...

Positive tilt upper level ridge axis extending from CA NE across
the Northern Rockies this morning will gradually shift east today
as a strong/compact upper level low moves into central BC. Sunny
and mild conditions will prevail across the forecast area today
with afternoon temperatures reaching values near 10 degrees above
seasonal averages. High level moisture spilling over the upper
ridge will bring some increased cloud-cover this afternoon and
surface winds will also become breezy late this afternoon along
the east slopes of the Rockies. No changes needed to previous
forecast. Attention then turns the upper low moving into BC, which
appears on track to bring strong winds to much of North Central
MT late tonight through Wednesday night.

&&

.SYNOPSIS...

High pressure ridge will bring mainly clear skies, dry conditions,
and above average temperatures in the 60s and 70s for today. A
cold front could then bring strong winds, cooler temperatures, and
scattered showers for Wednesday into Thursday. Damaging winds of
over 50 MPH may even be found across northern portions. Check out
the High Wind Highlights for the latest details. 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 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

&&

.PREV DISCUSSION...
/ISSUED 525 AM MDT Tue May 23 2017/

Today through Thursday...High pressure ridging over the region
will bring mostly clear to partly cloudy skies and warm
temperatures across the forecast area on Tuesday. By this evening
an upper level low will move from the Gulf of Alaska into British
Columbia. Models are in good agreement showing a strong jet streak
on the south side of this feature reaching the western border of
my forecast area late tonight. Have gone ahead and upgraded the
High Wind Watch to a warning for the Rocky Mountain Front and
adjacent plains with sustained winds likely to exceed criteria,
especially over the plains on Wednesday. Eastern portions of the
watch were NOT upgraded at this time since it will take an extra 6
to 12 hours for strong winds to reach this area. This will give
the day shift an opportunity to view one more model run before
making a decision for this part of the forecast area. A strong
cold front sweeps through North Central Montana with this weather
system for much cooler temperatures and unsettled conditions by
Thursday. mpj

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  58  60  43  58 /   0  10  40  40
CTB  51  54  40  57 /   0  10  40  30
HLN  53  62  44  61 /   0  10  30  40
BZN  48  64  38  58 /   0  10  20  30
WEY  39  65  29  51 /   0  10  10  20
DLN  49  62  36  57 /   0   0  10  30
HVR  56  64  45  61 /   0  10  40  40
LWT  52  64  40  55 /   0  10  30  40

&&

.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 Watch from Wednesday morning through Wednesday evening
Blaine...Chouteau...Hill.

&&

$$

weather.gov/greatfalls



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