Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 211002

Area Forecast Discussion
National Weather Service Glasgow MT
402 AM MDT Wed Mar 21 2018


Synoptic Setup: Short term begins with a ridge over the western
half of the CONUS which crests over central British Columbia and
Alberta. Coldest air of the northern hemisphere is bottled up over
the Nunavut. A trough of modified Pacific air splits off from
this airmass and flows into the Gulf of Alaska and bottoms out
offshore of Oregon.

Today through Thursday: As the ridge moves in from the west
daytime mixing will lift some of the moisture and dissipate it into
the free atmosphere, eliminating some cloud coverage and morning
fog by the afternoon. However, where conditions clear will allow
sunlight to begin melting more snow which will then reinforce the
moist layer overnight and fog and low cloud will probably come
right back after sunset in the late evening. The ridge itself
should transition by rather fast with a beautiful day Thursday as
well. Meanwhile, the trough off shore will move inland over the
Pacific Northwest.

Thursday night into Friday: Flow across the region will turn south
west with Pacific moisture and excess jet energy driving over a
cold surface layer. This will lead to mix of winter precipitation
including snow, rain, and possibly even brief freezing rain.
Forecast profiles seem to vary from areas to area, but this is
quickly becoming a serious question with the possibility of a
couple hundredths of an inch. PoPs with this system have ramped
up another 10%. So, confidence in a precipitation event is
increasing. However, confidence in a freezing rain event is still

Friday night through Monday: Southwest flow transitions as the
trough from the PCNW moves through. This will decrease
temperatures but also increase PoP chances back to seasonal
norms. COnfidence in this period is average.

Monday night onward: Large scale appears to be more towards a
ridge as high pressure builds up over the Intermountain West.
However several models bring shortwave along the International
Border which could easily change day to day output with multiple
models disagreeing in the ensemble. While conditions should warm,
any particular period could quickly cool back down with a 24 hour
shortwave. Confidence here is below average. GAH


FLIGHT CAT: VFR - Airport Shutdown.

SYNOPSIS: Dense fog has managed to develop over the hi-line along
river valleys and creeks. This includes KGGW and KOLF and has shut
down operations. Dense fog at these terminals is expected to lift
between 17 to 19Z. Looking at GOES-16 RGB nighttime micro-
physics, KSDY and KGDV may experience some fog overnight but it
should not become worse than IFR.

Winds: Light and variable this morning... becoming southeast to
east at less than 10 this afternoon... increasing to 10 to 20 kts
late Thursday morning.



Dense Fog Advisory until noon MDT today for Central and
Southeast Phillips...Central and Southern Valley...Daniels...
Eastern Roosevelt...Northern Phillips...Northern Valley...
Sheridan...Western Roosevelt.

Flood Watch through Thursday morning for Garfield...Petroleum.


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