Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
434 AM EST Wed Nov 28 2018

Valid 12Z Wed Nov 28 2018 - 12Z Sat Dec 01 2018


...Western U.S....

An impactful storm is forecast to move into California beginning
Wednesday, bringing very heavy snow accumulations to parts of the
Sierra.  Warm advection precipitation ahead of an approaching
shortwave is forecast to spread across California late Wed into
early Thu.  WPC probabilities continue to highlight the potential
for heavy snow accumulations across the higher elevations, with a
Moderate Risk for amounts of a foot or more for elevations above
7000 ft during the Day 1 period (ending 12Z Thu).  Snow levels are
expected to decrease as the shortwave moves inland.  With heavy
precipitation continuing, WPC probabilities show a Moderate Risk
for additional amounts of a foot or more for elevations above 6000
ft during the Day 2 period (ending 12Z Fri).  WPC probabilities
continue highlight a significant potential for amounts above 30
inches over the two day period. 

Meanwhile, mountain snows associated with low-amplitude energy
downstream of the primary shortwave will result in some locally
heavy high elevation amounts from the northern and central Nevada
mountains into the central Rockies Wed into early Thu.  Then the
previously noted shortwave will bring an additional round of snow
as it moves across the Great Basin into the Rockies, with higher
probabilities for heavy amounts across the Nevada mountains into
the central Rockies on Day 2.  Snows are expected to continue
across the central Rockies into Day 3, before waning late Fri into
early Sat as the trough moves east into the Plains.

Meanwhile back to the west on Day 3, models show another shortwave
trough moving into the Pacific Northwest and Northern California
late Fri into early Sat.  This system is expected to bring snows
producing some locally heavy accumulations to the southern
Cascades as well as the Klamath and Siskiyous ranges in Northern
California. 

...Northern Plains...

The upper level trough traversing the western U.S. on Days 1 and 2
is forecast to move east of the Rockies on Fri, assuming a
negative tilt as it pivots across the Plains late Fri into early
Sat.  There is some model signal for developing snows north of the
low moving out across the central Plains as well as along a
trailing surface trough extending back into the northern High
Plains.  However the overnight models showed limited agreement
with the evolution of this system and therefore confidence is very
limited as to if and where any heavy snow amounts might occur.

...Northeast...

While some areas of northern New York and northern New England may
see some additional significant amounts, snows will continue to
gradually diminish as the deep low centered over Maine translates
east later today.  Meanwhile strong northwesterly flow west of the
center will support some additional lake enhanced snow showers,
producing some additional locally heavy accumulations in the lee
of lakes Erie and Ontario on Wed.  Shortwave ridging moving across
the lakes will bring an end to the threat on Thu.

Pereira