Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
415 AM EDT Sat Apr 01 2023

Valid 12Z Sat Apr 01 2023 - 12Z Tue Apr 04 2023

...Northern Great Lakes...
Day 1...

The storm system responsible for the heavy snow and blizzard
conditions Friday and into Friday night will quickly track east
throughout the rest of the morning. The heaviest snowfall will
reside beneath the TROWAL tracking from northern WI to the U.P. of
MI. The latter of which will also have the benefit of some modest
lake enhancement. Snowfall rates of 2-3"/hr are expected beneath
this band with the eastern portions of the U.P. seeing the longest
duration of heavy snowfall. The forecast calls for another 6-12"
of snow in the eastern U.P. with a few inches also possible in the
central U.P. and far northern mainland MI. Strong wind gusts will
continue during the periods of heavy snow and on the backside of
the storm once snow diminishes in the afternoon. The heavy/wet
consistency of the snow weighing down tree branches and power
lines, along with the 40-50 mph wind gusts themselves, could
result in blowing snow and power outages. Updated Key Messages for
this system are below.

...Pacific Northwest to the northern High Plains...
Days 1-3...

...A major winter storm will produce heavy snow and strong winds
from the central Rockies to the northern High Plains early next
week...

The Pacific Northwest will be under siege from a strong and
persistent northeast Pacific jet stream that will introduce not
one but two different upper level disturbances to the region, as
well as into the northern Rockies. The left exit region associated
with this 250mb jet streak will remain positioned over the Pacific
Northwest and northern Rockies Saturday and into early Sunday,
which combined with ample Pacific moisture and strong upslope
enhancement into some mountain ranges, will result in heavy
snowfall. The second and more intense upper level feature arrives
Sunday morning as an amplifying upper low dives south into the
Pacific Northwest. Snow levels will drop below 1,000 feet in some
cases, while at the same time pushing the conveyor belt of Pacific
moisture south into northern California, the northern Great Basin,
and into the Wasatch and western WY mountain ranges. The heaviest
snowfall is set to occur along the Cascade Range of WA and OR
where snowfall will be measured in feet; anywhere from 1-4 feet is
expected with locally higher amounts possible in the tallest
peaks. Farther east, the northern Rockies mountain ranges which
include the Bitterroots, Boise, Sawtooth, and the Lewis Range can
also expect anywhere between 1-2 feet (locally higher).

Snow really begins to ramp up in the Wasatch, Tetons, Wind River,
and other central Rockies ranges of WY late Sunday night and into
Monday morning. It is during this time that the amplifying upper
trough produce strong PVA over the central Rockies while vertical
ascent atop the atmosphere increases while located beneath the
diffluent right-entrance region of a jet streak strengthening over
the northern High Plains. In addition, frontogenesis in the
700-500mb layer will support banded precipitation from these
aforementioned mountain ranges into eastern WY. By Monday
afternoon, an organizing and deepening 700mb low will form over
eastern UT and make its way northeast into southern WY. As ESE
winds in the 850-700mb layer pick up, it will introduce a large
quantity of moisture into the northern High Plains and wrap around
the northern periphery of the 700mb low. Meanwhile, temperatures
will be plenty cold enough to support snow, aided by the arrival
of a cold Canadian air-mass from the north. Heavy snow then looks
to engulf much of WY on east into western NE and western SD on the
northern periphery of a sub 990mb low in lee of the Rockies in
eastern CO late Monday and into Tuesday.

The pressure gradient will be impressive with the development of a
sub 990mb low in the central High Plains and a dome of 1030mb+
high pressure over southern Canada. The strong easterly component
in the central High Plains will cause strong upslope flow into the
front range of the Rockies, as well as 40-50 mph wind gusts by
Tuesday morning. With all the ingredients in place, this has all
the makings of a classic late season major winter storm in
portions of the central Rockies and High Plains. The question
marks involving this set up revolve around storm track and storm
motion. The slower the storm, the more time there is for heavier
snowfall accumulations, and vice versa for a faster storm. Latest
experimental PWSSI shows an expansive areas of 60-70% Moderate
impacts late Monday and into Tuesday from the Wasatch and Uinta
mountains to central and eastern WY. In fact, there are 60%
probabilities or Major impacts in portions of eastern WY,
southwest SD, and western NE late Monday into Tuesday. While there
is still some lingering uncertainty regarding the track, there is
increasing confidence in a high impact winter storm unfolding
beginning Sunday night and lasting into the first half of next
week. Key Messages are below.

The probability of significant icing Days 1-3 is less than 5%.


...Key Messages for Mar 30 - Apr 1 Winter Storm...

-Intense snow rates (1-2â€/hr, locally higher) combined with
strong winds may cause extensive tree damage and power outages
through Saturday morning across the Upper Midwest and into the
northern Great Lakes.

-Hazardous travel conditions due to a combination of snow covered
roads and whiteout conditions are expected.

-Periods of snow will taper off Saturday afternoon with gusty
winds potentially still capable of causing blowing snow and
possible power outages.

...Key Messages for Apr 3-5 Blizzard...

-A powerful storm will track across the Intermountain West and
central Rockies early next week before moving through the High
Plains and Upper Midwest mid next week.

-Confidence is increasing in a multi-hazard storm with significant
snow accumulations and strong winds. The combination of heavy
snowfall and strong winds could result in blizzard conditions
across portions of the central Rockies and the Plains.

-Widespread hazardous travel conditions and disruptions are
expected, including snow covered roads and reduced visibility,
particularly from Monday through Wednesday.

-In the wake of the storm, much below normal temperatures and wind
chill values near or below zero are likely, creating a dangerous
situation for those who may become stranded due to the heavy snow
and strong winds.


Mullinax