Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 182052

Area Forecast Discussion
National Weather Service GLASGOW MT
152 PM MST Wed Jan 18 2017

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

Upper trough was digging into California tonight then will slow
with it`s remnants moving into the Central Plains Friday. Another
trough Friday will pushing onto the West Coast.

For Northeast Montana, high cloudiness will be variable across the
area through Thursday with some thickening Thursday Night. That`s
when enough moisture/dynamics from the first trough brings
precipitation mainly to south-central Montana Thursday Night and
Friday. Low chances of snow showers then rain showers move east
across mainly the southern areas. The 12z ECMWF is a bit of an
outlier for late Friday where some deformation occurs over the
eastern zones, bringing slightly higher chances here.

Precipitation type should transition from snow to rain as temps
warm Friday.

850 mb temps stay above zero through the period, but cool from
+12C(yes, +12!) to +2C Friday. The Wetbulb temps Thursday Night
should allow for snow Thursday Night not Freezing Rain, but this
will continue to be watched. Jamba

.LONG TERM...Fri night through Wed...

An undercutting trough followed by a Sunday ridge, followed by
another undercutting trough Monday, followed by another ridge
Tuesday night will define the extended period. Most moisture will
be channeled around Northeast Montana, and temperatures will
begin slightly above normal then slowly trend down to slightly
below normal by mid-week. With no critical frontal timing issues,
will make only minimal changes to the extended period grids, and
mainly Friday night through Sunday by blending in the latest
guidance. Models timing and phasing drift apart for the next
system. So will only make minimal coordination edits for now.


Previous discussion -
Synoptic Setup: long range begins with a large trough over the
western half of the United States and Canada. A Pacific airmass
in habits this airmass from the Four Corners to central Alberta.
At that point arctic air takes over and runs north into Alaska. To
the west a large trough sets over the northeast Pacific with a
slightly cooler airmass than whats over northeast Montana.

Friday night onward: as the heat embedded in the previous ridge
exits to the east pacific air across the region will continue to
modify colder and colder over the snow pack each nigh period
through the long range. There are no major cold fronts within the
long range but there are more subtle features which bring ever so
slight cooler temperatures from one period to the next and long
with slight chance for very limited new snow fall in nearly every

The biggest frontal change and drop in temperatures appears to
happen when the second cooler trough from the pacific moves
across the area Sunday and get a slight modified arctic air
infusion. However models hold on just beyond the long range
around Thursday bringing in a warm pacific ridge into the region
again. So, no arctic plunge or big snowfall event is anticipated
at this time. GAH



VFR tonight through Thursday, with mid-to-high clouds.

The high pressure ridge across the local region will begin to
be knocked down tonight as an upper trough and Pacific storm
system push into the Pacific Northwest. Very little precipitation
will make it over the Divide. With temperatures well above
freezing today and slightly above freezing Thursday, expect
melting and patchy ice on surfaces.

Winds mostly southwest at around 5-10kt, except at KGGW where winds
may be more southeasterly at times. Late tonight and Thursday
most winds will be light and variable





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