Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
411 AM EDT Mon Apr 27 2020

Valid 12Z Mon Apr 27 2020 - 12Z Thu Apr 30 2020

...Northeast...
Day 1...

Surface low just southeast of Cape Cod at 06Z will extremely
slowly to the east over the next 12 hours as it becomes captured
by mid-level energy which will close off in response to phasing
shortwaves from the northern and southern stream. At the same
time, coupled jet structures responsible for at least subtle
deepening of this feature will lift more quickly to the northeast,
leaving this wave to meander to the east during D1. North and west
of this low, precipitation is ongoing this morning from eastern
Upstate New York through central Maine. Exceptionally dry air
filtering southward from northern Maine has eroded the edge of the
precip shield to the north, while a dry slot working northeast has
limited precipitation across most of Southern New England thus
far. As the low continues to pivot slowly eastward, modest
frontogenesis and deformation will continue to pivot into Maine,
with weak mid-level spokes of energy also rotating southwest
around the increasingly stacking low. While ascent will gradually
begin to wane, the aforementioned forcing should keep moderate
precipitation ongoing across ME and NH through the evening, with
some lighter precip drifting into Massachusetts this evening. Very
late April sun and marginal thermal profiles will offset any
cooling on the northerly flow, so accumulations greater than 2
inches should be confined to the mountainous areas of NH and ME,
as well as across central ME where better forcing will last just a
bit longer. The highest snowfall is likely near the Presidential
Range, where WPC probabilities for 6 inches are as high as 30
percent.


For Days 1-3, the probability of significant icing (0.25-inch or
greater) is less than 10 percent.

Weiss