Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
503 AM EDT Sun Apr 10 2022

Valid 12Z Sun Apr 10 2022 - 12Z Wed Apr 13 2022

...Western U.S. to the Northern Plains...
Days 1-3...
A late season, long duration winter storm, producing significant
snow and strong winds will likely impact the northwestern to the
north-central U.S. this period.

Unsettled weather will continue across the Northwest today as an
upper level shortwave and its associated frontal band continue to
move across the region this morning.  This will be followed by a
more amplified system moving into the region later today.  Models
show a closed low developing just east of Vancouver Island later
today before pivoting southeast into Washington and Oregon
tomorrow.  This will bring another round of heavier precipitation
and strong winds, followed by lower snow levels behind a strong
cold front moving across Oregon and northern California on Monday.
 In addition to heavy snows for the southern Washington and Oregon
Cascades, significant accumulations are possible along the higher
elevations of the coastal ranges as well.  Energy digging south of
the low will draw colder air and onshore flow farther south across
Northern California, supporting mountain snows with potentially
heavy accumulations spreading south from the Northwest California
ranges into the Sierra on Monday. 

As this system moves east, accumulating snows are likely to reach
down into the valleys of southeastern Washington, eastern Oregon,
and Idaho, with heavy accumulations possible for the Blue
Mountains into the northern and central Rockies from central Idaho
and western Montana to Utah on Monday into early Tuesday.  Snow is
expected to develop east of the Divide across the northern High
Plains Monday night into early Tuesday.  Increasing upslope flow
on the northwest side of a low moving east of the Rockies, along
with divergence aloft near a coupled jet, will support heavy snows
developing over the central to western Montana ranges Monday night
into Tuesday.  Meanwhile, persistent onshore flow ahead of another
system developing along the British Columbia coast will support
continued unsettled weather across western Washington and Oregon,
into Northwest California, with additional heavy accumulations
possible along the Cascades and coastal ranges.

On Tuesday heavy snow is likely to develop and spread east from
central Montana into parts of the Dakotas.  As the leading low
continues to track east, strong low-to-mid level frontogenesis on
the northwest side of a powerful, deepening surface low that is
expected to track northeast from the central High Plains to the
Upper Midwest, overlapped by coupled upper jet forcing, will
support heavy snow developing across the region.  Model spread
remains significant, with the GFS and GEFS Mean still faster than
the ECMWF, UKMET, and CMC to bring the low east into the northern
Plains Wednesday morning.  While the spread does lower confidence
in the details, heavy snowfall accumulations and strong winds will
likely impact a significant portion of southeastern Montana,
northwestern South Dakota and southwestern to central North Dakota
by early Wednesday.  WPC probabilities indicate that by Wednesday
morning widespread snowfall accumulations of 8-12 inches, with
locally heavier amounts are likely across the region.
    
...Northern Minnesota...
Days 1...
A shortwave moving east of the northern Rockies this morning is
forecast to track across the northern Plains today and then lift
north, assuming a negative tilt as it tracks across the Upper
Midwest tonight into Monday morning.  This dynamic system is
expected to support rain changing to snow across northern
Minnesota later today into early Monday.  Model consensus
continues to show that an inch or two of snow is likely, with some
potential for heavier amounts given the strong dynamics.

For Days 1-3, the probability of at least 0.1" icing is less than
10 percent.

~~~Key Messages for April 11-14 Winter Storm~~~

--A late season, long duration, significant winter storm is likely
to affect portions of the northern Rockies, northern Plains, and
Upper Midwest Monday into Tuesday.

--While uncertainty remains regarding the details of the track and
timing of this system, heavy snow and strong winds are possible
for many areas.

--The combination of heavy snow rates and strong winds could
produce blizzard and near-blizzard conditions, creating hazardous
travel.

--Heavy wet snow producing significant accumulations has the
potential to produce scattered power outages, tree damage, and may
impact livestock, especially young calves and lambs.

--Begin to prepare for impactful winter weather and hazardous
travel conditions this week.

Pereira