Area Forecast Discussion
Issued by NWS Great Falls, MT

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352
FXUS65 KTFX 181748
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1145 AM MDT Wed Oct 18 2017

.UPDATE...
Another windy day across Central Montana but gusts will likely only
reach into the 30kt range through the day. Expect cooler
temperatures and only a slight chance of some showers over the
Continental Divide.

&&

.SYNOPSIS...

A weak ridge of high pressure between a low pressure system
exiting to the east and the next Pacific system off the west
coast will bring dry conditions to the region today with
temperatures near to slightly above seasonal averages. Breezy
west to southwest winds will increase late today and tonight
across north central Montana with windy and warmer conditions
returning for Thursday. The next in a series of Pacific weather
systems moves across the region Friday followed by temperatures
cooling back to near seasonal averages with windy conditions
likely again this weekend.

&&

.AVIATION...
Updated 1745Z

Dry and stable westerly flow aloft continues across the region with
VFR conditions prevailing under scattered to broken high cloud-
cover. Surface winds will increase again by 20Z with gusts of 20-30
kts common over the plains of North Central MT and gusts 40-50 kts
along the Rocky Mtn front and adjacent areas (including KCTB).

&&

.FIRE WEATHER...

Increasing southwest flow aloft ahead of the next upper level
trough moving in from the Pacific will bring gusty winds and warm
temperatures to the region Thursday. Afternoon humidity is likely
to fall to the teens Thursday afternoon across central and
eastern portions of north-central Montana. Fire danger remains
elevated across grassland areas and critical fire weather
conditions are likely to occur Thursday afternoon and early
evening on the plains of north central MT. Hoenisch

&&

.PREV DISCUSSION...
/ISSUED 515 AM MDT Wed Oct 18 2017/

Weak upper level ridging passes across the region today between
exiting deep trough/surface low moving into Manitoba and next
upper trough moving from the Gulf of AK moving toward the BC
coast. Dry and slightly cooler conditions prevail today with
temperatures still somewhat above seasonal averages. Approach of
the next upstream tough toward the west coast will increase winds
aloft from the SW again later today and tonight with with a lee-
side surface trough re-intensifying late tonight into Thursday
morning. SW winds will increase again across north-central MT
during this period with strong winds potentially extending east
from the Rocky Mtn Front into eastern Glacier county by Thursday
morning. Flow aloft backs to more southwesterly during the day
Thursday, allowing for temperatures to surge back to well above
average levels levels again. Windy conditions are likely across
much of the area as SW winds aloft at 30-40 kts mix down during
the Thursday afternoon period. The offshore upper level trough
moves inland Thursday night and Friday with shortwave and surface
front moving east across the forecast area by Friday afternoon.
Precipitation will increase along areas near the continental
divide Friday as SW to W flow aloft moistens with showers also
possible as the front moves through SW MT this period.
Temperatures cool back to seasonal averages on Friday with snow
levels falling to near pass levels. Hoenisch

Friday night through Wednesday...Look for spotty, light showers to
persist following the passage of the cold front through the
overnight hours Friday night and into Saturday. As colder air
filters in from the north, temperatures will likely continue to
drop, along with freezing-levels leading to the potential for
accumulating snow for higher elevations of south-central and
southwestern MT, especially along the Madison, Bridger and Gallatin
Ranges. This system will quickly depart early Saturday leaving
behind clearing skies with cool afternoon highs. However, by
Saturday night clouds will begin to increase from the west as
another quick moving system swings across just north of the
MT/Canadian Border. Behind this system, models continue to
confidently illustrate the development of a strong jet aloft, which
will push eastward across the Northern Rockies into the early hours
on Sunday. This will likely yield yet another high wind event across
most of the CWA beginning Sunday morning, with the peak of the event
being in the afternoon hours. Given forecast H7 wind speeds ranging
between 55-75kts across the Plains, and even higher along the Rocky
Mountain Front, strong winds aloft will have no trouble transferring
to the surface via sufficient boundary layer mixing. Having said all
of that, I have adjusted forecast wind speeds reflect a more
realistic possibility of high winds following the jet aloft, timed
with the best diurnal mixing in the afternoon hours. Looking at the
synoptic pattern as we get into next week, long-range models have
persistently been advertising the development of a re-enforcing
ridge across the Southern Pacific coastline, which will reflect
increasing heights across the majority of the western US. As strong
ridging amplifies along the entire west coast, this will transition
the upper-level flow more from the northwest and aid in the
development of a dominant surface high across the northern Rockies.
This will likely keep temperatures near, to slightly above normal
while staying dry through the middle part of next week. KLG

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  64  51  75  47 /  10  10   0   0
CTB  59  44  67  38 /  10  10   0   0
HLN  67  44  74  42 /   0   0   0  10
BZN  69  40  73  41 /   0   0   0   0
WEY  54  27  58  31 /   0   0   0  10
DLN  66  37  68  40 /   0   0   0  10
HVR  63  47  76  41 /   0  10   0   0
LWT  65  46  75  44 /   0   0   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Watch from 9 PM MDT this evening through Thursday
morning Eastern Glacier...Northern Rocky Mountain Front...
Southern Rocky Mountain Front.

Fire Weather Watch from Thursday morning through Thursday
evening Central and Eastern Lewis and Clark National Forest
Areas...Chouteau and Fergus Counties...Hill and Blaine Counties.

&&

$$

weather.gov/greatfalls



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