Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
454 PM EST Tue Feb 04 2020

Valid 00Z Wed Feb 05 2020 - 00Z Sat Feb 08 2020


Day 1...

...Southern Rockies to the Ohio Valley...
A positively-tilted upper trough will continue to shift east from
the central Rockies and Southwest into the central Plains and
southern High Plains late Wednesday and Thursday.  As post-frontal
upslope flow contributes to some light to moderate amounts from
the Sacramento Mountains to the Davis Mountains in southern New
Mexico and West Texas, models continue to signal a moderate to
heavy snowfall event impacting portions of the southern Texas
Panhandle region into southwestern Oklahoma.  A favorable upper
jet couplet along with low-to-mid level frontogenesis is expected
to support moderate to heavy snowfall bands developing across the
region Wednesday evening through the overnight.  Several HREF
members indicate liquid precipitation rates of 0.10-inch an hour
translating northeast across the region during the overnight into
the morning hours.  WPC PWPF indicates that snow accumulations of
6-inches or more are likely  over this region.  Southeast of the
heaviest snow, models continue to show mixed precipitation, with
accumulating ice likely from portions of central Texas
northeastward into eastern Oklahoma. 

Farther to the east, models show a weak low level wave moving into
eastern Kansas and Oklahoma Wednesday morning.  Southerly winds,
drawing warm, moist air over the top of surface cold air
associated with a high pressure centered over the Great Lakes,
will support freezing rain from the Ozarks eastward into the Ohio
valley.  While widespread heavy ice accumulations are not
expected, WPC PWPF indicates amounts of 0.10-0.25 inch are likely
across portions of southern Missouri.


...Cascades to the Northern Rockies...
A low-to-mid level frontal zone is expected to shift east and
stall over western Washington as deep onshore flow ushers another
long fetch of moisture onshore -- supporting additional periods of
moderate to heavy precipitation along the orographically favored
terrain.  Heavy snow accumulations are likely for portions of the
Washington Cascades, as well as the Blue Mountains and central
Idaho ranges.

  
Day 2...

...Mid Mississippi Valley to the Northeast...
Low-to-mid level frontogenesis north of an amplifying surface wave
that is forecast to move progressively to the northeast through
the Ohio valley, is expected to support a swath of light to
moderate snows from the mid Mississippi valley to the upper Great
Lakes Wednesday night into Thursday morning.  South of the axis of
heavier snows, freezing rain, with accumulating ice is expected
across portions of the Ohio valley, especially from central
Indiana into northwestern Ohio.  East of the low, mixed
precipitation is expected to result in a broad swath of snow and
ice from the central Appalachians northward to the Northeast. 
Significant ice accumulations are possible for portions of the
central Appalachians, particularly along the Allegheny Mountains. 
Across northern New York and New England, where the precipitation
type is expected to remain mostly snow, moderate to locally heavy
accumulations are possible.

...Pacific Northwest to the Central Rockies...
Low-to-mid level frontogenesis, along with a series of weak
shortwaves embedded within in deep northwesterly flow, will
support periods of snow across the region, with heavy
accumulations possible from the central Idaho and western Montana
ranges to northern Utah and Colorado.  Rising snow levels across
the Northwest, should keep heavy snow accumulations there largely
confined to the higher elevations of the northern Cascades.

Day 3...

...Northeast...
Models show the initial wave moving into the Great Lakes
weakening, with a second low developing over the Mid Atlantic late
Thursday.  This second system, supported by a mid level shortwave
moving out of the base of the broader scale trough is forecast to
deepen as it moves from the Mid Atlantic to the Northeast on
Friday.  This system is expected to bring another round of mixed
precipitation to the Northeast, with heavy snow possible across
northern New England and accumulating ice across a good portion of
Upstate New York and central New England.

...Pacific Northwest to the Central Rockies...
The pattern is expected to remain mainly unchanged across the
region through Friday, with additional periods of snow and heavy
accumulations expected from the mountains of northern Idaho and
western Montana to central Colorado.

Pereira