Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 181118

Area Forecast Discussion
National Weather Service Great Falls MT
418 AM MST Sat Nov 18 2017

Updated Aviation Discussion


A broad ridge of high pressure will gradually shift east across the
region through the remainder of this weekend for dry condition with
with seasonably cool temperatures today warming slightly on Sunday.
Strong winds are likely to develop along the Rocky Mountain Front
on Sunday and spread east into western portions of north central
Montana late Sunday and Sunday night before a cold front descends
southeast into the region on Monday.



Today through Monday...Upper level ridge drifts east across the
region today and tonight for relatively quiet and dry conditions.
Substantial pressure gradient across the Rockies remains at the
surface for continued gusty winds along the east slopes of the
Rockies today and tonight with breezy west winds also developing
across the remainder of the forecast area later today with afternoon
mixing. The upper ridge begins to flatten Sunday in response to
shortwave energy dropping SE through BC, which eventually shears
east across southern Alberta Monday along with an associated surface
low, sending a cold front south through the forecast area in its
wake. Already strong west winds along the immediate east slopes of
the Rockies will increase further though the day on Sunday as winds
aloft increase under the flattening upper ridge. Models continue
to indicate 700MB flow at 60-75kts spreading out to the south and
east of the Rocky Mtn Front late Sunday and Sunday night, bringing
potentially strong winds to adjacent western portions of north-
central MT where a High Wind Watch is in place. A cooler airmass
slides south into the region Monday behind the shortwave and
surface low traversing the Canadian Prairies. Rain and snow
showers are possible Monday as the front progresses south through
the forecast area with orographically enhanced precipitation also
likely to be focused along the continental divide. Hoenisch

Monday night through Saturday...A high pressure ridge aloft will
reside over our CWA Monday night through Wednesday. However,
multiple disturbances should traverse the ridge from west to east;
the most prominent of which should affect the region on Tuesday.
This ridge is then forecast to be broken-down by several stronger
disturbances on Thanksgiving and Friday. In addition, a Canadian
cold frontal passage now looks to occur late Thanksgiving into
Friday morning. Model guidance is in good agreement that a high
pressure ridge aloft will then build eastward into our region on
Saturday. Atmospheric profiles remain favorable for periods of
strong, gusty downslope winds along the Rocky Mountain Front. Right
now, Wednesday through Thanksgiving is the window of greatest
concern for these winds.

The aforementioned pattern will be conducive to periods of upslope
precipitation along the Continental Divide and the Southwest MT
mountains. Elsewhere, isolated snow and/or rain showers are possible
Monday night through Wednesday, courtesy of the aforementioned
disturbances traversing the ridge aloft. POPs also increase late
Thanksgiving night through early Saturday, especially over Southwest
MT, where one or more bands of steadier precipitation may form along
the Canadian cold front. This progressive weather pattern will
result in variable temperatures. At this time, Tuesday looks to be
the coolest day of the long term period, while Wednesday should be
the warmest. In fact, Wednesday`s highs look to reach the 50`s to 60
degrees at many lower-elevation locations. These forecast readings
are about 15-20 degrees above-normal.


Updated 1118Z.

VFR conditions will prevail at area terminals with scattered to
broken mid level cloud cover over SW MT gradually diminishing
through Saturday morning but areas of broken high cloud-cover will
persist. Gusty surface winds will continue along the Rocky Mtn front
and increase at all area terminals this afternoon with moderate to
strong mountain wave turbulence likely along the east slopes of the
Rockies. Hoenisch


GTF  43  33  50  39 /  10   0   0   0
CTB  42  29  46  31 /  10   0   0   0
HLN  42  22  44  28 /  10   0   0  10
BZN  39  15  41  24 /   0   0   0   0
WEY  27   8  31  16 /  10  10   0  10
DLN  37  18  40  25 /   0   0   0  10
HVR  39  23  46  29 /   0   0   0  10
LWT  41  25  47  32 /   0   0   0   0


High Wind Watch from Sunday morning through late Sunday night
Cascade...Central and Southern Lewis and Clark...Eastern
Pondera...Eastern Teton...Judith Basin...Toole.

High Wind Watch from late tonight through late Sunday night
Eastern Glacier...Northern Rocky Mountain Front...Southern Rocky
Mountain Front.


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