Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
356 AM EST Thu Feb 14 2019

Valid 12Z Thu Feb 14 2019 - 12Z Sun Feb 17 2019


...Western U.S....

Multiple systems will continue to impact the mountains of the West
over the coming days, producing widespread snows with heavy
accumulations in some areas. 

Although a closed low nearing Northern California Thursday morning
is forecast to quickly weaken and advance east, this system is
expected to contribute to some heavy accumulations along portions
of the Sierra as well as parts of the Rockies from southern Idaho
to northern New Mexico.  WPC Day 1 probabilities (ending 12Z Fri)
show at least a Slight Risk of a foot or more across these areas,
with a High Risk across a large portion of the Sierra, as well as
for the Sawtooth, Teton and San Juan ranges.  An anomalously deep
low dropping south along the Washington and Oregon coast is
expected to bring lower snow levels and the threat for heavy
accumulations back to the mountains of Northwest California, with
additional snows for the northern Sierra Friday morning.  Even as
this system weakens and ejects inland, trailing energy dropping
south along the coast will maintain an anomalously deep trough
over the West, with periods of snow producing additional heavy
accumulations from southwest Oregon to the Sierra into Days 2 and
3.

...Central Plains and Ozarks to the Lower Ohio Valley and Central
Appalachians....

The remnant shortwave associated with the leading low moving into
California on Day 1 is forecast to move into the Plains on Friday,
producing a weak wave along a east-west oriented boundary
extending from the Tennessee valley back into the southern Plains.
 This will move moisture north over a shallow dome of cold air
extending south, supporting a stripe of mixed precipitation with
accumulating ice possible from the eastern Kansas-Oklahoma border
eastward across the Ozark region into the lower Ohio valley late
Friday.  WPC probabilities indicate a Slight Risk for ice
accumulations of 0.25 inch or more centered over southern
Missouri.  Farther to the north and within the deeper cold air,
expect snow to be predominant snow type, with significant snow
accumulations possible from eastern Nebraska and Kansas eastward
across the lower Missouri and mid Mississippi valleys.  Some light
snow accumulations are possible farther to the east as the system
moves across the central Appalachians on Saturday.

...Great Lakes and Northeast...

Phasing upper level energy over the northern Plains and upper
Midwest will support a deepening area of low pressure moving into
the upper Great Lakes late Thursday.  This system is expected to
produce a brief window of heavy snows for portions of northern
Michigan as it lifts across the region Thursday night.  Snow
developing in the warm advection pattern east of the low may
produce some significant accumulations across portions of northern
interior New England before changing over to rain on Friday.

Pereira