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fxus65 ktfx 181115 
afdtfx

Area forecast discussion
National Weather Service Great Falls Montana
515 am MDT Wed Oct 18 2017

Updated aviation discussion

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.

&&

Discussion...

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 Alaska moving toward the British Columbia
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 Montana
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 west flow aloft moistens with showers also
possible as the front moves through SW Montana 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
Montana/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 County Warning Area beginning Sunday morning, with the peak of the event
being in the afternoon hours. Given forecast 700 mb 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

&&

Aviation...
updated 1200z

Dry and stable westerly flow aloft continues across the region today
and tonight with VFR conditions prevailing under scattered to broken
high cloud-cover. Surface winds, which have largely subsided behind
an exiting low pressure system will increase again this afternoon
and evening. Gusts 20-30kts will be common tonight over the plains
of N-central Montana with gusts 40-50kts along the rocky mtn front and
adjacent areas including the kctb terminal. Hoenisch

&&

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 Montana. Hoenisch

&&

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 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.

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