Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
422 PM EST Sat Mar 09 2019

Valid 00Z Sun Mar 10 2019 - 00Z Wed Mar 13 2019


...Upper Midwest/Northern Great Lakes...

A negatively-tilted upper level trough and its associated surface
low will continue to lift northeast from the mid Mississippi
valley, with snows shifting east across the region through the
overnight hours into early Sunday, before tapering off as the low
tracks east of the lakes into eastern Ontario late in the day. 
Heaviest additional accumulations are expected to center north of
the low, with WPC Day 1 probabilities (ending 00Z Mon) showing a
High Risk for 4-inches, with a Slight Risk for 8-inches or more
across northern Wisconsin and the Upper Peninsula of Michigan. 
Some additional heavy amounts are also possible farther to the
west into northern Minnesota ahead of a northern stream trough and
its associated frontal boundary pushing east into the region. 

...Central Appalachians to the Northeast...

A warm front lifting out ahead of the aforementioned low is
expected to support precipitation moving north across the region
late Saturday into early Sunday.  Observations show high pressure
and dry air in place, with dew points well below freezing in many
spots.  This is expected to support a period of mixed
precipitation with some light snow, sleet and/or ice accumulations
possible from the central Appalachians into the Northeast.  How
long the cold air will remain in place is a bit of an uncertainty,
however most areas outside of the Adirondacks and northern New
England mountains should see a changeover to rain as high pressure
gives way and the warm air surges north.  Again, mainly light snow
and ice accumulations are expected, with some locally heavier
totals in the Adirondacks and northern New England mountains,
where WPC Day 1 probabilities are showing a Moderate Risk for snow
accumulations of 4-inches or more.

...Southwest to the Central and Southern Rockies...

A positively-tilted upper trough, with a developing closed low, is
forecast to drop south along from the Pacific Northwest and
eastern Pacific into California on Sunday.  While there is not a
strong signal for widespread heavy snow accumulations, there is
the potential for some locally heavy amounts from the coastal
ranges of northwest California extending eastward into central
Nevada and northern Utah along a low to mid level baroclinic zone.

The low developing along the northern California coast on Sunday
is expected to drop farther south along the coast to northern Baja
on Monday.  Moisture through Day 2 is expected to remain fairly
limited, hampering the potential for widespread heavy snow
amounts.  However, areas of enhanced ascent may be sufficient for
some locally heavy totals, especially in some of the
orographically favored regions such as the San Juan Mountains in
southwest Colorado, where WPC Day 2 probabilities are indicating a
Moderate Risk for accumulations of 8-inches or more. 

Models show the low rotating east along the western U.S.-Mexico
border on Tuesday.  Energy digging south of the low is expected to
amplify the flow, supporting increasing moisture advection across
eastern Arizona and western New Mexico into the central Rockies. 
This will support the potential for significant snows along the
eastern Mogollon Rim into the White Mountains of Arizona, with
additional heavy accumulations possible for the San Juan Mountains
and the Sangre de Cristos Mountains.

...Pacific Northwest...

Snow is expected to return as an amplifying upper level trough and
associated cold front sweeps across the region Monday night into
Tuesday.  Portions of the Cascades may see some locally heavy
accumulations, with WPC Day 3 probabilities indicating a Moderate
Risk for amounts of 8-inches or more.  As cold air drops in behind
the front, snow levels may drop to around 500 ft across western
Washington late Tuesday.

Pereira