Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 170400
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
900 PM MST Mon Jan 16 2017

.UPDATE...

Little updates needed this evening. Mid to high level clouds
currently found across the Rocky Mountain Front into the northern
plains. High pressure will break down tonight...with strong winds
creating dry downsloping air. As a result...pulled the slight pops
out of the Rocky Mountain Front tonight through tomorrow morning...as
looks like any precip should remain more on the west side of the
divide if anything should occur. With no major weather maker to
break the inversion in the Helena Valley tonight...added back in
the mention of haze through at least tomorrow morning. More mixing
is expected for the Helena Valley tomorrow...so perhaps air
quality can improve. Strong westerly flow still looks to be the
story for Tuesday...bringing strong winds...but still below High
Wind Warning criteria for northern and central areas. Current
wind forecast still looks valid...so left them mainly untouched.
Some rain and snow showers will be possible across the Rocky
Mountain Front...with just some increased cloudiness elsewhere.
Anglin

&&

.AVIATION...
Updated 2320Z.

VFR conditions will persist across the area through Tuesday with
varying amounts of high cloud-cover tonight followed by increasing
mid-high level cloud cover by Tuesday afternoon as flow aloft
becomes more westerly. Cannot rule out some periods of reduced
visibility at KHLN due to haze, mainly later tonight. Surface winds
will gradually increase from the W/SW at KCTB and KGTF later tonight
through Tuesday afternoon. Hoenisch

&&

.PREV DISCUSSION...
/ISSUED /

Tonight through Wednesday...Cold air remains trapped in southwest
valleys under strong temperature inversion. However, observations
suggest the inversion is weakening as a few lower elevations
locations did mix out with moderating temperatures today. Will
continue this trend tonight with valley temperature below zero,
then allow mixing and moderating temperatures at more locations
Tuesday afternoon. Ridging aloft flattens tonight as the upper
level jet reorganizes further south into the PacNW. A tightening
surface pressure gradient along the Rocky Mountain Front will
result in a period of strong winds developing later tonight and
continuing through Wednesday. The period of strongest winds is
expected Tuesday night into early Wednesday. Model guidance has
provided inconsistent solutions regarding peak winds at the
surface, and with little evidence of a mechanism to bring 75kt
winds aloft down to the surface, will keep wind forecasts below
high wind criteria and discontinue the high wind watch. Pacific
moisture advances into the Northern Rockies, with 1-3 inches of
light snow developing late Tuesday through Wednesday over the
interior mountains near the Continental Divide. PN

Wednesday night through Monday...Medium range models appear to be
in good agreement through the entire forecast period. Period
starts off with weak ridging over the northern Great Plains, a
weak upper low over the Southern Plains and a trough along the
Pacific Northwest coast. This trough is expected to progress
inland and gradually weaken Wednesday night through Thursday as a
secondary trough in the Gulf of Alaska moves southeast and
strengthens into a closed low off the Washington coast. These two
features then merge to form a broad upper level trough over the
western USA with temperatures cooling back toward seasonal
averages for north central Montana. With the broad trough in place
across the region, most precipitation is expected to be well
south of Montana. However, occasional disturbances will be ejected
from the main trough bringing a chance for precipitation to the
mountains and portions of southwest Montana but only a slight
chance for light showers across the north central plains. Main
portion of the upper trough drops into the Desert Southwest and
progresses into the southern Great Plains over the weekend.
Shortwave ridging behind this trough builds into the Great Basin
but will likely not be strong enough to influence Montana weather
as another broad upper trough develops over the western USA for
continued cool conditions into early next week. mpj

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  29  43  35  47 /   0   0   0  10
CTB  29  42  30  46 /   0   0   0  10
HLN   4  29  21  37 /   0  10   0  10
BZN   6  31  15  40 /   0  10   0  10
WEY  -1  23   5  27 /   0  10   0  10
DLN  13  35  19  38 /   0  10   0  10
HVR  22  41  34  46 /   0  10   0  10
LWT  23  47  35  48 /   0   0   0  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

weather.gov/greatfalls



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