Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 170405 AAB

Area Forecast Discussion...UPDATED
National Weather Service Glasgow MT
905 PM MST Sat Dec 16 2017

9pm Update:

Guidance brings a possibility of some very patchy freezing fog
overnight. Will add some patchy freezing fog to some of the
favorable locations around the area. Otherwise kept the forecast
going as planned.   Proton

6pm Update:

Upper trough continues over the Rocky Mountain States this
evening. Fair skies continue with clouds and snow to the south of
the region. This trend is well handled in the current forecast. No
changes.  Proton

Previous Discussion:

Things get a little more active mid-week with snow then cold.

Weak upper trough passing through eastern Montana will slowly
exit to our east as broad upper ridge builds east. However the
ridge will not reach too far into Montana as a strong Pacific jet
stream will have a greater influence. Most of the precipitation
however will get wrung out over the Rockies leaving northeast
Montana under periodic clouds. The exception will be Monday when a
cold front drops south and could squeeze out some snow or rain
showers. Amounts are expected to be light.

On Tuesday, upper disturbance over Gulf of Alaska grabs some
arctic air and drops southeast. Pacific moisture streaming into
the area pushes east with snow falling mainly over the western
and northern areas Tuesday Night.

The upper system then drops southeast Wednesday. Dynamics
materialize quickly with strong lift and dendritic growth
expected. Most areas may pick up a general 2 to 4 inches with
possibly 6 inches in the Little Rockies. Issued an HWO to address

An arctic airmass then drops south with surface high pressure
settling into the area Wednesday Night. With clear skies, light
winds and fresh snowcover, expect temperatures to drop below
model guidance. This would result in lows below zero across the
north, single digits south.

The models then diverge on solutions a bit but agree to leave the
area under a northwest unstable flow. TFJ




There is a slight possibility that some low cloud or valley fog
may form late tonight into early Sunday.

Otherwise, winds will become light south late tonight, then
increase from the SW Sunday afternoon. TFJ




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