Area Forecast Discussion
Issued by NWS Glasgow, MT

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FXUS65 KGGW 181105

Area Forecast Discussion
National Weather Service Glasgow MT
405 AM MST Mon Dec 18 2017


A shift in the overall pattern is expected to lead to accumulating
snow by midweek, followed by much colder temperatures.

A split upper trof is currently moving across the western CONUS,
with the northern portion heading across the northern Plains
states toward the Great Lakes, and the southern portion in the
form of a nearly entirely cutoff low over the Sonoran desert
region of the US and Mexico.

A surface boundary has set up over northern Montana, bringing
cloudy skies and a mixture of rain and snow showers this morning.
These will continue off and on throughout the day as this trof
slowly moves south and east through the region, and some locations
across far northeast Montana may see between half an inch to an
inch of snow.

Just behind this, a low pressure system will push into the area
from the northwest, allowing cold air to push into Montana from
the north. This system will bring snow to the region beginning as
early as Tuesday afternoon, which will persist into Thursday
morning. Currently, the highest snowfall amounts are anticipated
to be across the higher terrain of the Little Rockies. Areas of
northeast Montana north of the Missouri River should also see
higher snowfall amounts due to the surface boundary expected to
set up as cold air tries to push down from the north side of this
storm. Current forecast snow amounts look to be 5 to 8 inches over
the Little Rockies, and 3 to 5 inches over the rest of the area
north of the Missouri, with generally 2 inches or less south. As
these totals are anticipated from Tuesday morning through
Wednesday afternoon, a Winter Storm Watch has been issued for this
time period. Winds may also be somewhat breezy as this front
passes through, and we will keep an eye on that as the storm
approaches to determine how significant impacts from that will be.

Cold air will push in from the north, and with fresh snow cover,
temperatures will drop to near or below zero Wednesday night.

Cold northwest flow will keep temperatures cold, and there is
increasing model consensus regarding the probability of an upper
level low diving down in the Great Basin region from the Pacific
Northwest on Thursday. So have a chance of snow south of the
Missouri for Thursday night into Friday as this system passes,
although current thinking is that the precipitation will remain to
our south and over the Rockies with this storm.

Beyond this, model guidance diverges, although at this time it
looks like northeast Montana will remain cold under a generally
unstable northwest flow regime through Christmas.  Hickford



LLWS: Low level winds shear will be possible in the morning


SYNOPSIS: A disturbance will push through the region, bringing a
dense cloud deck with lowering ceilings throughout the day.
Ceilings may dip into MVFR levels periodically today, mainly with
mixed precipitation or as rain transitions to snow. A rain and
snow mix is possible at all sites through the day, transitioning
to snow by mid afternoon.

WIND: West-southwest at 5-15 kts through the morning...
veering to the northwest and increasing to 10-20 kts this
afternoon after the disturbance passes.



Winter Storm Watch from Tuesday afternoon through Wednesday
afternoon for Central and Southern Valley...Daniels...Eastern
Roosevelt...Northern Valley...Sheridan...Western Roosevelt.

Winter Storm Watch from Tuesday morning through Wednesday
afternoon for Central and Southeast Phillips...Northern
Phillips...Southwest Phillips.


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