Accumulation potential for southern New England (National Weather Service)

UPDATE, 4 p.m.: Blizzard watches and winter storm watches in effect for Boston and New York City have been upgraded to blizzard warnings. In New York City, the amount of snow predicted has increased to 10-14 inches, with locally higher amounts possible.

From earlier: Confidence continues to grow that Boston will face a major to historic blizzard Friday into Saturday. New York City may also experience a period of blizzard conditions, but questions remain about how much precipitation falls as snow. Washington, D.C. will likely just get grazed by rain and, perhaps, a little wet snow at the onset.

“This is likely to be a memorable blizzard with 18 to 24 inches of snow expected across portions of Connecticut, Rhode Island, Massachusetts, New Hampshire and Maine,” says Wes Junker, Capital Weather Gang’s winter weather expert. “Pockets of 30 inches or more are a good bet.”

Related: As blizzard nears Northeast, airlines cancel flights, waive fees

The official National Weather Service forecast for Boston calls for 18-24 inches of snow, with snowfall rates of 2 to 3 inches per hour and winds gusting as high as 65 mph Friday night and Saturday.

“Travel may become nearly impossible with blowing and drifting snow,” the NWS cautions.

NAM model shows an intense storm off the coast of southern New England very early Saturday morning (

AccuWeather paints a rather apocalyptic picture for eastern New England:

Strong winds will not only cause white-out conditions and massive drifts, but also coastal flooding and power outages. Gusts can approach hurricane force in coastal areas. If the power goes out, it could take a while for crews to repair the lines.

It also highlights the potential for thundersnow.

While the more reliable models generally simulate 18-24 inches for Boston, some have simulated stunning totals over 30 inches, which would best the all-time record. Here are the top 10 storm recorded at Logan Airport:

1. February 17-18, 2003: 27.5 inches
2. February 6-7, 1978: 27.1 inches
3. February 24-27, 1969: 26.3 inches
4. March 31-April 1, 1997: 25.4 inches
5. January 22-23, 2005: 22.5 inches
6. January 20-21, 1978: 21.4 inches
7. March 3-5, 1960: 19.8 inches
8. February 16-17, 1958: 19.4 inches
9. February 8-10, 1994: 18.7 inches
10. December 20-22, 1975, January 7-8, 1996, and December 26-27, 2010: 18.2 inches

More likely, the storm will ranked between number 5 and 10.

A ways down the coast, the storm may not be historic, but certainly impactful. In New York City, a winter storm watch has been posted for 6 to 10 inches of snow and the possibility of damaging winds gusting to 60 mph - mainly Friday night. The forecast there is complicated by the possibility of snow changing to rain.

“For now...[we are] expecting a surge of warmer air ahead of the low on Friday that would change initial snowfall to rain,” the NWS office serving New York City writes. “But if that warmer air does not make it...then widespread snow would fall throughout the region...and snowfall totals would have to be increased.”

The cause of the storm is the explosive combination of two weather disturbances.

“A strong northern stream system will translate its energy to a southern stream low coming up the coast,” says Junker. “The latter will pull lots of moisture northward setting the stage for a major blizzard for the northeast as the low bombs out and slows off the New England coast.”

This translation will occur north of Washington, D.C.’s latitude, meaning the nation’s capital will dodge the bullet. For now, we expect a possible brief period of wet snow or mixed rain and snow Thursday night, changing to some rain Friday morning as the storm begins to pull away and subsequently explode.

While the storm will not meaningfully impact Washington, D.C., if you have travel plans from east central Pennsylvania to central New Jersey and especially on north into southern New England, be prepared for severe delays and/or cancellations Friday and Saturday (possibly lingering into Sunday) and consider altering your plans.