Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
417 AM EDT Thu Apr 11 2019

Valid 12Z Thu Apr 11 2019 - 12Z Sun Apr 14 2019


...Northern Plains and Upper Midwest...

A powerful spring storm will continue to produce heavy snows with
strong gusty winds as it drifts northeast across eastern Nebraska
into western Iowa on Thursday.  Supported by strong upper forcing
and low to mid level frontogenesis, heaviest snow accumulations
are expected to center from eastern South Dakota and southeastern
North Dakota into west-central Minnesota.  For the 24-hr period
ending 12Z Friday, WPC probabilities indicate a Moderate to High
Risk for accumulations for 12-inches or more across this region. 
East of the heavier snow axis, a wintry mix is expected, with
significant sleet and ice accumulations possible across portions
of Wisconsin and northern Michigan.  For the Day 1 period (ending
12Z Friday), WPC probabilities show a Slight to Moderate Risk for
ice accumulations of 0.25-inch or more from the southern
Wisconsin-Minnesota border northeastward into the U.P. of Michigan.

By early Friday, models show the system beginning to weaken as it
moves farther to the northeast into the upper Mississippi valley. 
Then by late Friday, models show the system beginning to
accelerate northeast into eastern Canada.  For the Day 2 period
(ending 12Z Saturday), WPC guidance shows the potential for heavy
snow accumulations rapidly decreasing, with only a Slight Risk for
additional accumulations of 4-inches or more centered across
portions of northern Minnesota. 

...Central and Southern Rockies into the High Plains...

Energy currently well upstream over the Gulf of Alaska is expected
to dive southeast, supporting an amplifying trough over the
Southwest-Four Corners region Friday evening.  As it shifts
farther east Friday night, cold air aloft along with a period of
upslope flow is expected to support accumulating snows along the
Colorado Front Range into the Sangre de Cristo Mountains Friday
into Saturday.  WPC probabilities for the Day 2 period (ending 12Z
Saturday) show a Slight to Moderate Risk for snow accumulations of
8-inches or more across this region.

Models show the system continue to amplify as it moves farther to
the east, with a closed upper center and strong surface cyclone
developing over northern Texas on Saturday.  While confidence is
limited, both the NAM and ECMWF support the idea of rain changing
to accumulating snow across portions of the High Plains along the
back edge of the associated comma-head.  WPC Day 3 probabilities
(ending 12Z Sunday) show a Slight Risk for accumulations of
4-inches or more extending from southeastern Colorado and
northeastern New Mexico into western Kansas and the Oklahoma and
Texas Panhandle regions.

...Pacific Northwest...

Models show an upper level shortwave and surface low moving into
British Columbia on Saturday.  Decreasing snow levels behind the
trailing cold front moving across the Northwest Saturday night may
support significant snow accumulations across portions of the
northern Cascades.  For the Day 3 period, WPC probabilities
indicate a Slight Risk for accumulations of 8-inches or more for
portions of the western slopes above 3000 ft.

Pereira