Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
317 PM EST Wed Feb 27 2019

Valid 00Z Thu Feb 28 2019 - 00Z Sun Mar 03 2019


...Pacific Northwest/Mountains of Northern-Central California to
the Northern Rockies/Northern Plains...

On Day 2, confluent flow produces bands of 700 mb convergence and
an upper level jet streak that moves east across northern and
central CO.  This will likely result in widespread snow, including
locally heavy accumulations across the Colorado Rockies to the WY
border.

Another significant mid/upper level wave will push onshore the
central California coast during Day 3, bringing another plume of
moisture. Snow levels will lower and this should yield heavy snow
across the Sierra Nevada range where the highest totals could
exceed 2 feet. As moisture tracks eastward, moderate to locally
heavy snowfall will be possible across the Utah mountains and
Colorado Rockies.

...Great Lakes/Northeast...

Day 1...

Early in the day 1 period, deeper moisture within a zone of
mid/upper level divergence will persist across portions of the
Northeast and New England. The low/mid level wave is expected to
pass east of the area overnight tonight, by 12z Thursday.
Additional snowfall up to 4" will be possible around the Boston
metro with lesser amounts westward toward central NY State.

...Mid-Atlantic...

Day 2...

An area of low pressure will lift out of the southern US toward
the mid-Atlantic region while an upper level shortwave swings
across the lower Great Lake. Increasing isentropic lift will lead
to precipitation breaking out across late Thursday night into
Friday morning. Thermal profiles suggest snow or a wintry mix will
be possible across portions of WV, northern VA toward the MD/PA
border. There remains differences in QPF placement, forcing
strength, and also thermal profiles. The NAM was considerably
colder and thus had higher snowfall potential while the GFS/ECMWF
were lighter and further south, which kept accumulating snow
potential much lower. For this cycle, leaned on the GFS/ECMWF
consensus, and showed a stripe of 1-2" from WV toward
western/central MD with embedded probabilities of 2-4". Overall
forecast confidence is lower than average.

...Upper Mississippi Valley/Upper Great Lakes...

Day 3...

Energy coming out of the Northern Rockies will track across the
Northern Plains and Upper Midwest Thursday and Thursday night
across the Great Lakes. With enhanced moisture advection and
forcing for ascent, light snow is expected. QPF amounts are
relatively light and with the faster speed of the whole system,
amounts will be generally below 4 inches. The greatest probability
for seeing 4" lies across eastern SD into west-central MN.

The probability of a quarter inch of icing is less than 10 percent
days 1-3.

Taylor