Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 161751

Area Forecast Discussion
National Weather Service Great Falls MT
1045 AM MST Mon Jan 16 2017

Updated Aviation Discussion.


Quiet weather prevails across the forecast area this morning.
Valley inversions continue to maintain subzero temperatures and
air quality concerns. Temperatures should reach the teens for most
of these valleys but otherwise are not expected to mix out with
warmer air aloft. High clouds will increase from the northwest
with increasing jet stream energy through western Canada. Updated
the forecast to better match observed trends in temperatures and
increasing high clouds. PN


Updated 1745Z.
VFR conditions across the area through 18z Tue as flow aloft
transitions from an upper ridge to increasing westerly flow. Expect
smog/haze to continue through the Helena valley through this
evening. Some mid/high level clouds will be on the increase across
the region mainly after 03z Tue, with light showers developing over
the Rocky Mountain Front by 12z Tue, with the western mountains
gradually becoming obscured towards 12z Tue. West to southwest winds
will also begin to increase this evening and continue through the
overnight along the Rocky Mountain Front. Cassell


/ISSUED 440 AM MST Mon Jan 16 2017/
Today through Wednesday...The upper level flow aloft will
gradually become more westerly tonight through Tuesday. As a
result, expect dry conditions today, with increasing chances for
precipitation later tonight through Wednesday over the Rocky
Mountain Front and mainly across the mountain areas of Southwest
MT. Overall for our area, precipitation amounts will be on the low
side through Wednesday, with 2 to 5 inches of snow possible in
the Rocky Mountain Front, most of which will fall right near the
divide, and much lighter snowfall expected in the Southwest
mountains, generally less than 1 inch. Winds will be on the
increase, and the latest models have delayed the stronger winds
until Tuesday morning, thus the high wind watch has been adjusted
a bit. Otherwise, expect a slow warming trend through Wednesday,
with afternoon highs in the 40s and 50s over North Central MT
Tue/Wed. In Southwest MT, very cold temperatures will continue for
another day/evening. With a general snow pack of 6 to 12 inches at
lower elevations, combined with good radiational cooling last
night, and again this evening, temperatures will remain cold
before increasing cloud cover late tonight starts to limit the
cooling a bit. Then on Tuesday, expect some mixing to occur over
the valleys, slowly helping to mix out the colder air, but it will
take time, and most valley locations will likely not go above
freezing until at least Wednesday. Brusda

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


GTF  34  28  46  39 /   0   0   0  10
CTB  37  29  46  35 /   0   0  10  10
HLN  13  -1  32  20 /   0   0   0  10
BZN  14  -3  34  17 /   0   0   0  10
WEY  10 -13  23   6 /   0   0  10  10
DLN  15   5  35  21 /   0   0   0  10
HVR  30  22  45  36 /   0   0   0  10
LWT  34  23  48  35 /   0   0   0  10


High Wind Watch from Tuesday morning through Tuesday afternoon
Eastern Glacier...Northern Rocky Mountain Front...Southern Rocky
Mountain Front.


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