High-Impact Nor’easter to Impact the Mid-Atlantic and New England

GFS parallel snow accumulations

Brief Synopsis

This week’s storm system of interest has now moved away from the West Coast and begun to dig into the Four Corners region. The vigorous shortwave will continue amplifying across the Southern Plains on Tuesday. By Wednesday, it’ll begin lifting east northeastward across the Mid-South, Mississippi Valley, and Tennessee Valley. Later Wednesday, the wave will push into the Ohio Valley, the Mid-Atlantic, and New England, bringing a powerful winter storm along the East Coast from Wednesday into Thursday.

Timing

After dropping snow across the Rockies, precipitation will develop along and ahead of the shortwave across the central and southern Plains on Tuesday. The wave will trigger the development of a surface low along the Gulf coast on Wednesday, as a large swath of precipitation overspreads the Southeast, Tennessee Valley, Ohio Valley, and Mid-Atlantic. Precipitation will then begin to overspread southeastern New England by Wednesday evening, continuing into Thursday. Rain and possible storm development in the warm sector of the system will aid in the amplification of a downstream ridge. The strength of this ridge will determine how closely the surface low rides along the Mid-Atlantic and southeastern New England coast after departing North Carolina and Virginia.

Expected position of the surface low off the Mid-Atlantic coast on Wednesday evening

Forecast Model Discussion

The operational, along with many of its ensemble members, have continued to show a more southern track of the surface low, primarily due to a weaker downstream ridge. In such a scenario, the axis of heaviest snowfall rates and accumulations would occur from around D.C. (and northern Virginia) to Philly to Long Island to Cape Cod. Areas just northwest of this line would still get noteworthy but lower amounts. The GFS-parallel, a version of the GFS still in its testing phase, has consistently been the northern outlier. This solution would largely be a miss for D.C., Philly, New York City, Long Island, and Cape Cod, but copious amounts of snow would fall northwest of this line, including over Boston.

Projected 24hr Snowfall accumulations from Wednesday morning to Thursday morning, according to the GFS-parallel model. Additional snow will fall across parts of New England Thursday afternoon.

The European model, along with the shorter-range 12km NAM, has the surface low trekking quite close to the Mid-Atlantic after moving just offshore. Both models keep the low far enough off the southeastern New England coast for the heaviest snow accumulations to still fall over Philly, NYC, Long Island, and Cape Cod.  

Most model guidance indicates that downstream ridging mid-week will be flattened by the current storm system exiting New England today. However, this ridge should be more amplified than what models suggest. For that reason, I gave the GFS-parallel and the shorter-range RGEM model (not discussed above) more weight in the snow accumulation forecast below. If there’s not a northward shift in most model guidance by tomorrow afternoon, I’ll adjust my forecast to align more closely with the operational GFS, European, and other short-range guidance.

Matthew’s Snowfall Accumulation Forecast for Select Cities

Washington, D.C.: 1-3 inches

Philly: 3-6 inches

New York City: 3-6 inches

Long Island: 1-3 inches

Providence, RI: 12-18 inches

Boston: 12-18 inches

Cape Cod: 1-3 inches

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Winter Prepares To Visit The Northeast

Written By: Robert Millette

A coastal low will develop into the first Nor’Easter of 2015 this weekend as the first real snowfall for the year will hit sections of the Northeast region. By late Friday, low pressure will develop over Georgia and pass off the coast of the Outer Banks Saturday morning. Rain will begin on the Eastern Shore and Southern sections of Maryland and in Delaware Friday afternoon. While it will be mostly rain in these areas, snow will begin to fall in the Eastern panhandle of Maryland overnight with a mix and possible icy situation near the Baltimore and D.C metro areas. These areas will cool and begin to change to snow with the exception of right along the coastline of the Chesapeake. Extreme Northern areas of the Eastern Shore and Delaware will also begin to transition to a mix overnight as snow begins to move into New Jersey and Pennsylvania.

By Saturday morning, snow should have moved into the NYC metro area and the coastal areas of Connecticut and Rhode Island. By noon time on Saturday, snow should arrive in Boston with a rain/snow line setting up south of there as the Cape and Islands will see rain along with the New Bedford/Fall River metro region along the South coast of Massachusetts. Snow and rain will be tapering off or have already ended in Maryland, Delaware and Southern New Jersey by this time, but another area of precipitation will move into Coastal portions of this area for a time on Saturday afternoon.

During the afternoon, snow will move into the Southern and coastal areas of New Hampshire and Maine as the storm passes Southeast of Nantucket and moves toward Nova Scotia. Precipitation should wind down during the afternoon in New York and Saturday evening in the Boston metro region.

While exact totals are not set in stone at this time, several inches of snow can be expected from an area starting Northwest of DC and Baltimore passing through Philadelphia and NYC on towards Hartford and Boston. Locations north of Boston will see a drop off in the amounts of snow as this storm will be out at sea and not pass close enough to the coastline to give them significant snowfall.

Winter Storm Watches have been posted for Hampshire, Worcester, Central and Northwest Middlesex, Western Essex and Western Norfolk counties. 4-7 inches of snow are expected on Saturday in this area by the National Weather Service. I expect this area to expand to include more Eastern locations as certainty increases. Winter Weather Advisories will be posted as the timeframe approaches.

Beyond this weekend’s storm, an Alberta clipper-type system looks to rapidly develop in the Monday/Tuesday timeframe and may bring more snow to the region. This storm will need to be watched closely for further developments.