Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
355 PM EST Sat Jan 26 2019

Valid 00Z Sun Jan 27 2019 - 00Z Wed Jan 30 2019


...Great Lakes/Northeast...
...Days 1-2...

An energetic shortwave and clipper low pressure system are
forecast to traverse the Great Lakes and Northeast tonight into
Sun. The system will produce relatively light snowfall amounts for
most areas. Lake effect enhancement will increase snowfall totals,
especially across the Upper Peninsula of Michigan and portions of
northern Lower Michigan, as well as across Upstate New York
downwind of lake Ontario.


...Northern Plains to Upper MS Valley and Great Lakes...
...Day 1 through Day 3...

Another amplifying mid/upper-level shortwave and clipper low
pressure system (the leading edge of another frigid arctic air
mass) will dive southeastward across the northern plains/Midwest
late Sun into Mon. The energetic nature of this system with decent
mid/upper-level dynamics will support a swath of snow across much
of the northern plains, Upper Midwest, and Great Lakes. The
strongest signal in the guidance for heavy snow is on Day 2 (Sun
night-Mon) from portions of southern/central WI east into portions
of Lower Michigan, with snowfall totals in this area likely to
exceed 8 and possibly even 12 inches in a mesoscale band just
north of the surface low track. By Day 3 (Mon night-Tue) the
surface low will move east-northeast into the lower Great Lakes
and Ontario/Quebec, with the best upper-level support quickly
shifting north of the Great Lakes/New England. Thus, expect light
to moderate snowfall amounts across the lower Great Lakes and
portions of the Northeast on Day 3, with the heaviest amounts
likely at the higher elevations from WV/PA north into Upstate NY.


...Ranges of central to southern MT/WY and CO...
...Days 1-2...

Confluent flow through a  deep layer drives the persistence of a
deep layer north-northwest jet across the northern plains through
early Sun. Upper divergence maxima cross MT near a jet streak and
into WY and also the Black Hills of adjacent SD, targeting the
Bighorn Mountains/Black Hills on day 1 with several inches of
snow. On Sun, the next in the series of 300 mb jet maxima drops
south from Canada across MT and then downstream into WY, with
embedded upper divergence maxima triggering lift and snow focused
on the ranges impacted in MT and WY, extending into the mountains
of north central CO. Lighter amounts are expected focused on the
front range of CO into the Sangre de Cristo mountains of southeast
CO/northeast NM as the upper jet builds south across these areas. 


...Lower MS Valley/TN Valley/Southeast/Southern Appalachians...
...Day 3...

Arctic cold front will quickly advance across the region late Mon
into Tue with largely anafrontal precipitation suggested by model
guidance. Precipitation is expected to begin as rain for many
areas but should quickly change to sleet and then snow as the cold
air mass rushes in behind the front. A swath of accumulating snow
is expected from portions of the lower MS Valley northeast to the
TN Valley, interior Southeast, and southern Appalachians.
Development of a potential weak wave of low pressure along the
front as indicated by a number of model solutions has some
potential to enhance snowfall amounts in a mesoscale band across
portions of northern AL/GA, where ensemble guidance suggests some
potential for exceeding 4 inches, although confidence is low at
this point as to exactly where this band would set up. Somewhat
greater confidence in 4+ inch amounts exists at the higher
elevations from northeast Georgia northeastward along the spine of
the Appalachians.


The probability for significant icing is less than 10 percent
nationwide days 1-3.


Ryan