Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 171608

Area Forecast Discussion
National Weather Service GLASGOW MT
908 AM MST Tue Jan 17 2017

.SHORT TERM...for northeast through Thu...

Main concern for the forecast continues to be range of
temperatures under a very shallow inversion. Most ridge tops
already above freezing with valley locations still in the teens.
Expect continued modification of the airmass today although the
valleys will likely struggle to reach freezing as shortwave energy
is lacking for improved mixing. Made slight adjustments to
temperatures and winds. Also increased sky cover as high clouds
streaming across the divide. Ebert

Previous short term discussion...Synoptic Setup:short term begins
with a large ridge nosing in over California and Oregon running
over the intermountain west and spilling over the Montana Front
range where it is forming a chinook and finally cresting over
Manitoba and The Dakotas. Farther west a large trough is forming
over the northeast Pacific behind the ridge. Most of the coldest
air of the north hemisphere is being held in place over Alaska and
its north slope.

Today through Thursday: Chinook ridge will bring warming
conditions over the next 3 days with highs above freezing,
especially over higher terrain. River valleys will struggle to
make it out of freezing today due to missing sufficient shortwave
radiation to melt through snow and warm the ground in addition to
mixing out the inversion fully. Chinook winds should easily
transport excess moisture away from their origin point of snow
melt... so low stratus and fog will be hard to create until night
time. Chinook should begin lightening by Thursday and this may
allow some low stratus to form and stay in place longer than the
other periods. GAH

.LONG TERM...Thu night through Tue...

Flow aloft will be southerly Thursday Night and Friday as a broad
upper trough moves into the Western US with an upper low off the
BC coast. A weak cold front Thursday Night could bring a slight
chance of rain and snow showers to the southwest part of the
forecast area.

Temperatures will be some what cooler on Friday but still above
normal. Shortwaves within the broad upper trough will move north
across the Plain States Saturday Night and Sunday bringing
chances for light snow into the area. At the same time, the main
trough splits and the southern branch moves to the east while the
northern branch lifts north into the Canadian Prairies by next
Monday. A shortwave ridge will bring dry weather to the area on
Monday. Then, the upper low that will be off the BC coast over the
weekend, moves inland as an upper trough early next week and
could bring a chance of light snow to the forecast area on
Tuesday. Forrester



Expect VFR - with mid to high broken clouds.

An upper level ridge is in place over the Pac-NW and Montana
prairie today. This has generated a northerly flow aloft. A
Pacific storm off the Washington coast is sending moisture into
the upper flow which is producing broken mid-to-high clouds over
Northeast Montana. A disturbance in the upper flow will begin to
knock down the ridge and bring an increase in mid-level clouds
tonight. This disturbance will also increase mixing to the surface
at times to aid in the warm-up, which may cause slippery surfaces
and depending on winds, possibly a chance for fog tonight and
Wednesday morning. No plans yet to add BR or FG to TAFs. Will re-
evaluate again.

Winds becoming southwest today at around 5-10kt, except KGGW winds
may be more southeasterly at times.





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