Winter Storm Riley has bombed out and is clobbering the Northeast as an intense nor'easter with damaging winds and heavy, wet snow, as a significant, long-lived, destructive coastal flooding event is now underway.
"Take this storm seriously!" the National Weather Service in Boston warned via Twitter. "This is a LIFE & DEATH situation for those living along the coast, especially those ocean-exposed shorelines."
Low pressure just off the southern New England coast underwent explosive development known as bombogenesis, defined by a rapid drop in atmospheric pressure of at least 24 millibars in a period of 24 hours or less. From 7 p.m. EST Thursday to 3 p.m. EST Friday, the pressure dropped from 1000 millibars to 975 millibars, or a 25-millibar drop in only 20 hours.
Thanks to a recent split of the polar vortex and a subsequent westward-shifting blocking high-pressure system near Greenland, the weather pattern is conducive for this nor'easter to move very slowly.
This will produce high winds over a sizable swath of the East, and coastal flooding will reach moderate or major severity over multiple high-tide cycles into the weekend.
Cold air is limited but sufficient to produce heavy, wet snow along the northern flank of the low-pressure system in the interior Northeast.
Water inundated parts of the Massachusetts coastline during the first high-tide cycle late Friday morning.
Moderate flooding has been observed at tide gauges in Scituate and Boston Harbor. The storm tide at Boston Harbor peaked at its third-highest level on record, only topped by Winter Storm Grayson in January and the Blizzard of 1978.
A car floating in floodwaters in Braintree, Massachusetts, prompted a water rescue.
Snow continues to blanket parts of central and eastern New York state, eastern Pennsylvania, New Jersey, northern Delaware and parts of western New England. This includes the Philadelphia metro area, where near-blizzard conditions have been reported at times.
Some wet snow has mixed in with rain in the New York City metro area and in Baltimore.
Richmondville, New York, in the Catskill Mountains, had picked up 35 inches of snow as of mid-afternoon Friday, with the town of Jefferson not far behind at 33 inches.
Other notable heavy snow totals as Friday afternoon included 19 inches in Coolbaugh Township, Pennsylvania, 14.5 inches in Syracuse, New York, 13.2 inches in Highland Lakes, New Jersey, 12.7 inches in Rochester, New York, 12.1 inches at Buffalo-Niagara International Airport, 11.9 inches in Albany, New York, and 11.2 inches in Erie, Pennsylvania.
High winds are currently raking parts of the mid-Atlantic states, Appalachians and New England.
A 93-mph wind gust was observed in Barnstable, Massachusetts, early Friday evening. On Nantucket Island, winds gusted as high as 89 mph while an 88-mph gust was reported in Woods Hole, Massachusetts.
Winds gusted to 71 mph at Washington-Dulles and 62 mph at Reagan National Airport Friday morning. New York's JFK Airport gusted as high as 67 mph early Friday evening. A 74-mph gust was clocked atop Chickaree Summit, Pennsylvania.
Dulles Airport reported gusts over 50 mph for more than 12 hours straight, a rare occurrence, according to the National Weather Service.
Gusts up to 63 mph have buffeted Boston-Logan Airport, and trees have been downed in many parts of Massachusetts, Rhode Island, Connecticut, New York, New Jersey, Pennsylvania, Ohio, Maryland, Virginia and North Carolina.
Numerous reports of trees down have also come in from the Washington D.C. metro, many blocking roads and a few falling onto homes and buildings.
High wind warnings stretch from Maine to the southern Appalachians, including virtually the entire Interstate 95 urban corridor from Boston to Washington D.C.
These areas can expect to see wind gusts to 60 mph, with locally higher gusts over 70 mph, capable of downing trees and knocking out power.
Occasional gusts to 60 mph may occur from southern Maine to the mid-Atlantic states and Appalachians into early Saturday. These winds will slowly taper off during the day Saturday in these areas.
The high winds, combined with heavy, wet snow in the interior Northeast (discussed in the "rain/snow" section below), will likely down trees and trigger widespread power outages in the East.
The National Weather Service just outside of Washington D.C. warned "the duration of the winds...will hamper the repair of power lines and tree removal" from this "prolonged, high-impact windstorm."
These long-lived winds blowing over a long stretch of the ocean, piling onshore and persisting for several days, will lead to moderate to major coastal flooding along parts of the Northeast Seaboard. Coastal flooding could be life-threatening along the Massachusetts coast.
Coastal flood warnings have been issued by the National Weather Service from southern Maine to North Carolina's Outer Banks.
Widespread coastal inundation is likely on parts of the Massachusetts coast, as well as many other stretches of the East Coast, including Long Island, the Jersey Shore, Delmarva Peninsula, Outer Banks of North Carolina and the coast of southern Maine.
This coastal flooding will occur over a number of high tides, which began Friday morning and will continue in some areas into Saturday night or even Sunday. Flood waters will be very slow to recede between high-tide cycles.
Water levels may be 3 to 4 feet above normal tides along the eastern Massachusetts shore.