Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
451 PM EDT Sat Mar 30 2019

Valid 00Z Sun Mar 31 2019 - 00Z Wed Apr 03 2019


...Eastern Great Lakes and Northeast...
Day 1...

A surface trough has setup downstream of troughs interacting over
the Midwest. The southern stream shortwave is shifting into IL
from MO while the southern end of the northern stream trough
extends from northern WI across western IA. As these troughs begin
to phase tonight, surface low development on the leading surface
trough enhances as it moves from Lake Erie to Lake Ontario. This
will enhance frontogenesis and allow ongoing rain to changeover to
snow particularly over northeastern OH and western NY tonight into
Sunday. However, the window for snow before dry air shifts in is
short and only a couple inches or less are likely from Cleveland
to Buffalo. Precipitation type guidance is often applied every six
hours with much of the precip quantity attributed to the type at
the end of the period, artificially enhancing snow. Therefore much
of the guidance going into the WPC winter ensemble falls victim to
this and is erroneously giving moderate probabilities for 4 inches
on the east side of Lake Erie (and moderate probabilities for two
inches into central OH) tonight. This is a good issue to address
for next winter.

The surface low quickly shifts up the St. Lawrence Valley Sunday
with a continuation of rain ending as snow, but amounting to an
inch or less across interior New England during the day Sunday.

Wrap around winds from the low will allow some lake effect snow
downwind of Lakes Erie and Lake Ontario Sunday. An additional inch
is possible locally east of Lake Erie with more favorable
conditions allowing moderate probabilities for four inches on the
Tug Hill Plateau east of Lake Ontario Sunday into Sunday night.


...Colorado/New Mexico...
Day 1...

A secondary shortwave trough from Oregon will close into a
mid-level low over UT/CO tonight. Moderate to heavy snow is likely
above the snow elevation around 5000ft Sunday, especially in the
San Juans and Sangre De Cristos of CO/NM where Day 1 probabilities
are moderate for 8 inches. Lighter accumulations are likely
elsewhere across the terrain south from central CO and across NM,
with WPC probabilities indicating a 10-20% chance for 4 inches as
far south as the Sacramento Mountains in NM.


...Northern Rockies...
Day 3...

An upper level jet stream diving from Western Canada into the
Northern Rockies will induce lift, coincident with moisture ahead
of a system approaching the West Coast will spilling into the
region. Forcing is generally transient, and snow levels are quite
high, 5000-7000 ft south of Montana, but moderate to heavy snow is
possible Monday. The heaviest amounts are forecast in the ranges
of NW WY, where WPC probabilities are moderate for 6 to 8 inches
across the Big Horn, Wind River, and Absaroka Mountains.


...Oregon/Northern Great Basin...
Day 3...

Low pressure reaches the OR coast Monday night and shifts inland
to ID Tuesday. Snow elevations begin high under a mid-level ridge
Monday, but lower to around 6000ft as the parent trough shifts
inland Monday night. Day 3 WPC probabilities are moderate for six
inches in the higher OR/CA Cascades, Blue mountains, and central
ID mountains.


The probability for significant freezing rain (0.25 inches) is
less than 10 percent all 3 days.


Jackson