Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 092120

Area Forecast Discussion
National Weather Service GLASGOW MT
220 PM MST Fri Dec 9 2016

.SHORT TERM...for northeast Montana...tonight through Sun...

The evening begins with Arctic high pressure centered over the
local region and an upper ridge axis in line with the Northern and
Canadian Rockies. An upper closed low centered over Vancouver
Island will be ejecting Pacific moisture into the PacNW. The low
opens up as it moves inland tonight, knocking down the ridge and
sending moisture across the Divide. In the process the surface
high will be nudged east.

Saturday the resulting disturbance begins to spread the moisture
across the Northern High Plains, a relatively warm moist air mass
over the Arctic air-mass at the surface, a perfect recipe for
snow. The disturbance will move through rather quickly, limiting
the snow amounts. The disturbance will also energize the east
winds tonight into early Saturday evening. With the cold surface
temperatures persisting, wind chills will continue to be an issue.

Main challenge was determining QPF and snow amounts. A blend of
preferred models resulted in 2-3 inches of snow across the north
and east beginning late tonight and ending Saturday evening. Wind
chills will begin with sunset and continue through noon Saturday.
Combined the winter hazards into a winter wx advisory from 5pm
today to 11 pm saturday.

Sunday will see a weak ridge follow which will produce slightly
warmer highs, around 5F to 10F warmer than Saturday.


.LONG TERM...Sun night through Fri...

Both models showing a sizable Pacific storm moving inland and
spreading qpf across a vast portion of the western States late
next week. The ECMWF brings it in earlier than the GFS solution,
about Friday-Friday Night. It also has been more consistent.
Therefore adjusted pops slightly toward the ECMWF solution.
Otherwise, it looks like Forecast Builder procedure didn`t change
much from previous forecast. TFJ

Previous Discussion...
Synoptic Setup: long range begins with zonal flow over most of
the CONUS. Coldest air over the northern hemisphere is centered
over northern Saskatchewan with the airmasses influence extending
south into central Montana. A second wave of extreme cold air has
jostled out of Siberia and is moving its way across the arctic
ocean just north of Alaska.

Sunday night through Monday: A little bit of pacific moisture
passing through from the zonal flow will override the new cold
airmass moving through the region to generate stratiform snow
showers during these periods. Total snow will be light with maybe
1 to 2 inches.

Monday Night through Thursday: center of the first airmass will
slide southeast and then move into Quebec. Northeast Montana may
warm slightly with maybe some highs in the teens rather than
single digits. Meanwhile the second wave of arctic air will roll
down the high plains of alberta and knock on the international

Thursday night onward: Some models are taking the second wave of
cold air and rather than kicking it eastward, centering it over
Montana. This will plunge temperatures when combined with any
previous snowfall into some of the lowest seen thus far this year.
Confidence here is moderate. GAH



VFR/MVFR ceilings expected into Saturday, then possible IFR in
snow Saturday afternoon.

Clouds will become a broken deck around 3K FT AGL tonight then an
area of snow will move in from the west driving visibilities to
less than 3SM at times in snow. Ceilings/Visibilities improve from
west to east Saturday Night.

WINDS: Light Easterly winds will increase to 10-15 kts this
evening and sustaining through Saturday.



Winter Weather Advisory until 11 PM MST Saturday for Central and
Southeast Phillips...Central and Southern Valley...Daniels...
Dawson...Eastern Roosevelt...McCone...Northern Phillips...
Northern Valley...Richland...Sheridan...Southwest Phillips...
Western Roosevelt...Wibaux.


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