Weather Service Report


974 
FXUS65 KGGW 231053
AFDGGW

Area Forecast Discussion
National Weather Service Glasgow MT
353 AM MST Sun Feb 23 2020

.DISCUSSION...

With precipitation expected to begin moving from central Montana
into Phillips, Garfield, and Valley Counties within the next 12 to
15 hours, felt it was warranted to issue a Winter Weather Advisory
for expected snow accumulations of 2 to 4 inches for all zones
except Petroleum County.

Forecast challenges will focus on the timing and amounts of the
snowfall with this winter storm, including the impact of blowing
and drifting snow, as well as a drop in temperatures for a few
days.

Weather pattern shows a near zonal flow today as the pronounced,
cold, upper level low pressure trough moves up and over the
continental divide tonight. In response, mostly sunny skies this 
morning will become cloudy and overcast from the west by mid-day 
today.

Model precip data has lined up fairly well, showing an intial push
of banded snowfall from west to east late tonight through early
Monday. The exact track of the low pressure center and its
associated dry slot is still uncertain. A few model differences
remain, but consensus blends I used, have covered most of that 
uncertainty. For example, early Monday morning, the NAM wants to 
keep that first push of banded snowfall in a line from Opheim 
through Scobey and Culbertson, while the GFS keeps it in a line 
from Malta through Jordan and Circle. Overall, the effect of the 
dry slot seems to bring lesser snow amounts to Petroleum County.

During the day on Monday, as the low pressure trough matures into
a closed low center, the dry slot finally saturates and fills in
the snow fall as the storm moves south through the remainder of 
eastern Montana and western North Dakota. Expect the last 
lingering snowfall to move south of our CWA during the early 
morning hours on Tuesday.

A widespread 2 to 3.5 inches of snow is expected with this storm.
The higher amounts seem to be favored along and north of US
Highway 2 and along the higher elevations along either side of the
Yellowstone River Valley.

Mid level winds in excess of 30 kts, may be brought down to the
ground with any precipitation, especially early Monday morning
through Monday afternoon. If this happens to coincide with the
banded snowfall, blowing and drifting snow would easily become a
problem. But, it also may only be associated with the dry slot.
Next shifts will need to closely watch these additional details
for hopeful increases in confidence.

Beginning Tuesday afternoon, a strong NW flow aloft and
approaching high pressure from the west will drive any
precipitation away and warm temperatures back up above normal.

A brief short wave disturbance in the NW flow Wednesday night
through Thursday will bring a slight chance for light
precipitation. 

Friday through Saturday, another strong ridge of high pressure
will keep things warm and dry for next weekend.

---BMickelson



&&

.AVIATION...

DISCUSSION: Today through tonight, a weak ridge of high pressure 
to our south, gives way to an approaching cold low pressure system
from the Canadian Rockies. Ceilings will begin to drop later this
afternoon and evening and snowfall is expected later tonight. 
After the winter storm spends most of Monday in the region, it 
will clear away by Tuesday morning.

FLIGHT CONDITIONS: VFR this morning, MVFR this afternoon, then 
IFR to VLIFR in blowing snow late tonight and through the 
overnight hours.

WINDS: Light and variable this morning, turning more out of the
south and southeast up to 15 kts by this afternoon, then from the
west up to 20 kts after 09Z in blowing snow.

---BMickelson


&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 9 PM this evening to 5 AM MST 
Tuesday for Central and Southeast Phillips...Central and 
Southern Valley...Daniels...Dawson...Eastern Roosevelt...
Garfield...McCone...Northern Phillips...Northern Valley...
Prairie...Richland...Sheridan...Southwest Phillips...Western 
Roosevelt...Wibaux. 

&&

$$

weather.gov/glasgow

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Western Regional Climate Center, wrcc@dri.edu