Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 162155

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


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


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


GTF  28  47  38  47 /   0   0   0  10
CTB  30  43  34  46 /   0   0   0  10
HLN   5  32  19  37 /   0  10   0  10
BZN   3  32  16  40 /   0  10   0  10
WEY -13  16   5  27 /   0  10   0  10
DLN   9  34  21  38 /   0  10   0  10
HVR  21  42  35  46 /   0  10   0  10
LWT  23  48  34  48 /   0   0   0  10



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