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469
FXUS65 KTFX 230450
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1050 PM MDT Wed Oct 22 2014

.UPDATE...A deep upper level trough is over the Gulf of Alaska
with a strong jet pushing inland along the Pacific Northwest coast
tonight. This system is feeding abundant mid and upper level
moisture into the Northern Rockies for increasing clouds across my
forecast area overnight. Have updated forecast to increase cloud
cover based upon latest satellite observations and model trends
but the remainder of the forecast is in good shape and no
additional changes were made. The High Wind Watch for the Rocky
Mountain Front was also left unchanged. However, in my opinion, 00Z
NAM model depiction of mountain top winds and surface pressure
gradients do not appear very favorable for a high wind event
Thursday night. In many respects I would expect stronger winds to
occur late tonight and Thursday morning but even these winds
appear only borderline at this time. Will pass my concerns on to
the midnight shift since there will be several more models that
will come in overnight that may help clarify the situation. mpj

&&

.AVIATION...
UPDATED 0450Z.
VFR conditions are expected to prevail for the next 24 hours. Winds
will decrease slightly overnight...but are expected to restrengthen
by mid morning over the Rocky Mountain Front and adjacent Plains and
continue to remain strong for the remainder of the TAF period.
Expect increasing mid/high level clouds over the region through the
period. Suk

&&

.PREV DISCUSSION...
/ISSUED 555 PM MDT Wed Oct 22 2014/
This Afternoon through Friday Evening...Plenty of clear skies across
the region this aftn as a weak high pressure ridge traverses the
state.  But latest visible satellite imagery already shows leading
edge of high cloud cover associated with a shortwave trof moving
through WA/OR reaching the northwest corner of MT.  This shortwave
is the first of several that will eject from a very deep and cold
closed low pressure system anchored in the Gulf of Alaska over the
next several days.  Though water vapor satellite imagery shows a
good-sized moisture plume accompanying this wave, it also indicates
a distinct split in the plume with much of the moisture heading into
southern BC/Alberta and the secondary swath heading across southern
Idaho.  That leaves our region in the low-moisture area between the
swaths, which is very well depicted in current forecast model
solutions that indicate widespread increasing clouds tonight and
tomorrow but any notable precipitation stays along the Continental
Divide, with some spotty showers over southwest MT.  As the trof
axis goes by Thurs aftn, mid- and upper-level winds increase
strongly over western portions of Glacier/Teton/Pondera counties and
continue into Fri morning.  Although the situation is overall
marginal for warning-criteria winds (58 mph or more), consistent
model solutions over past several runs gave us enough confidence to
post a high wind watch for the northern/southern Rocky Mtn Front
areas for Thurs/6pm to Fri/noon.  Other than the strong winds,
Friday`s weather still looking quiet as westerly downslope flow
should keep the foothills and plains precipitation-free.  High
temperatures remaining in the low-mid 60s on Thurs/Fri. Waranauskas

Friday Night through Wednesday...Long term models in relatively good
agreement with larger features and timing, but showing some
differences in finer details. Period starts with an upper level high
pressure ridge covering much of the western U.S. with the next in
the series of low pressure troughs approaching from the west. Both
GFS and ECMWF show several small weather systems embedded in the
trough in a disorganized fashion though placement and strength of
these small systems varies between the models. At this time, the
trough is expected to push into central Montana late Saturday
afternoon or Saturday night, and may bring some precipitation,
mainly to the west and southwest mountains. With the current
progressive pattern, the trough moves off to the east fairly
quickly, and the high pressure barely has a chance to start
rebuilding Tuesday before the next area of low pressure sweeps in
Tuesday night. These back to back troughs are expected to bring in
some slightly colder air. Once again, could see some precipitation
with trough passages the middle of next week, but best chances
for this remain over the mountains.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  45  65  46  60 /  10  10  10  10
CTB  41  63  41  58 /  10  10  10  10
HLN  40  66  44  61 /  10  10  20  20
BZN  33  65  39  61 /   0  10  20  10
WEY  24  52  31  51 /   0  10  20  10
DLN  37  63  42  59 /  10  10  20  20
HVR  39  69  43  63 /   0  10  10  10
LWT  40  67  43  61 /  10  10  10  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WATCH from Thursday evening through Friday morning
Northern Rocky Mountain Front...Southern Rocky Mountain Front.

&&

$$

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