Area Forecast Discussion
Issued by NWS Glasgow, MT

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000
FXUS65 KGGW 090424
AFDGGW

Area Forecast Discussion
National Weather Service GLASGOW MT
924 PM MST Thu Dec 8 2016

.SHORT TERM...for northeast Montana...tonight through Sat...
Update

Temperatures are dropping quickly over the eastern zones where
there is deep snow cover. Went below guidance for eastern areas
overnight. Continued wind chill advisory with marginal winds for
the advisory area. Otherwise forecast was in fairly good shape.

Previous Discussion

Wind Chill Advisory is now in effect until
noon Friday for Prairie, Garfield and parts of Valley counties.

Arctic high pressure over the Prairie Provinces will drift
southeast into the Northern Plains Friday, then into the southeast
United States Saturday. Some Pacific moisture will override the
Arctic airmass with a batch of snow moving in late Friday Night
then exiting to our east Saturday afternoon. Amounts look to be
around 2 inches with lesser amounts near the Canadian border.

East winds will be blowing at 10-20 mph with the snow, so there
will likely be issues with drifting snow and wind chills. TFJ


.LONG TERM...Sat night through Thu...

A disturbance that will affect the short-term period will have
moved through the area by the beginning of the extended period
Saturday night. There will still be lingering effects such as low
stratus and continued cold temperatures. A small, collapsing ridge
becomes zonal for Sunday. The short-lasting ridge will have been
knocked down by an approaching trough from the north. This trough
will be anchored by a closed low that is currently residing over
Baffin Bay between Greenland and Nunavut, Canada.

This cold low will work its way down over the Prairie Provinces
by early next week, sending a cold front through Northeast
Montana. Models are suggesting snow with the front for Monday. The
low center moves east into Ontario by Tuesday night. This movement
will bring in additional frigid Arctic air and increase winds for
an additional chance for hazardous wind chills Monday night
through Tuesday night.

Models also suggest another trough sending more Arctic air into
the area for the following weekend.

Overall, made minimal corrections, mainly from Day 3 night through
day 5 based on the latest guidance. Model are in fairly food
agreement for cold to continue.

Templer

Previous discussion -
The extended period gets underway Saturday night with fairly
zonal upper level flow across the region and a weak shortwave
pushing through the area with a little light snow.

As the wave departs and surface high pressure returns to the area
from Canada expect a reinforcement of Arctic cold air. By Monday
night model 850mb temperatures range from -20C to -27C across the
CWA. This weather pattern will help keep the track of shortwaves
embedded in the flow further south, and so expect any snow chances
to remain across the southern zones of the CWA during this time.

By the middle of next week an upper closed low will track across
Hudson Bay with an amplifying trough in the eastern U.S. helping
to develop a ridge across the Pacific shore. As this occurs the
flow aloft over eastern Montana into the rest of the Northern High
Plains will become northwesterly. Over time the ridge will
translate east, helping to spread higher 500mb heights across the
region and moderating temperatures, at least relatively speaking.
Look for high temperatures to perhaps make a run toward double
digits again by Thursday if this scenario pans out.

Latest 00z models show any ridge abruptly departing downstream
with a new shortwave trough developing over the western U.S. This
may initiate a new period of unsettled weather conditions, though
timing/placement of any snow is difficult at this time given large
ensemble spreads at these time scales. Nevertheless, it looks like
for right now at least, that things become more interesting toward
about December 15-16. As model consensus improves, more detail
will be able to be agreed upon, but for right now will introduce
slight chance to chance pops across the CWA to finish out the long
term forecast period. Maliawco


&&

.AVIATION...

SYNOPSIS: Solid patches of low stratus decks are floating around
the region overnight and periodically impacting the terminals.
These patches are big enough to hold for a couple hours and then
give way to clear skies. Will have to handle them with amends in
and out of BKN/SCT 015.

By the end of the cycle snow showers will present themselves with
the entrance of a shortwave Saturday morning.

WINDS: light and variable this evening, then becoming easterly
early friday morning and increasing to 5-15kt by the afternoon.

GAH



&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
Wind Chill Advisory until noon MST Friday for Central and
Southern Valley...Garfield...Prairie.

&&

$$

weather.gov/glasgow


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