Winter Storm Jonas to Become Dangerous East Coast Snowstorm; Blizzard Watch for D.C., Baltimore, NYC

NOTE: This article is no longer being updated. For the latest, see our current Winter Storm Jonas forecast story.

Winter Storm Jonas is kicking off Thursday with an initial round of snow and ice, and will turn into a major snowstorm Friday into the weekend over a large swath of the East Coast. Heavy snow is expected to fall across parts of at least 15 states, with blizzard conditions possible over parts of the Washington D.C., Baltimore and New York City metro areas. Winter Storm Jonas will also feature strong, possibly damaging winds, significant icing and coastal flooding.

(MORE: What is a Blizzard?)

As of Thursday morning, just over 73 million - or roughly one in every four Americans - were covered by either a blizzard watch, winter storm watch, winter storm warning, winter weather advisory, or freezing rain advisory from southeast Nebraska to the Carolinas to the New York City metro area. 

(INTERACTIVE: Winter Alerts/Radar)

A blizzard watch was posted for much of the New York City metro area, and continues for the Baltimore and Washington D.C. metro areas. 

Some or all of the largest cities in the Northeast - Washington D.C., Baltimore, Philadelphia, and New York - will be significantly impacted by this storm with heavy snow and strong winds, bringing travel to a grinding halt, between Friday afternoon and Sunday morning.

(MORE: Interstate Travel Forecast | One of All-Time Great Storms?)

Winter storm warnings are posted from the Carolinas to the Appalachians, Ohio Valley, Tennessee Valley, Mid-South as far west as central Arkansas. Among the many cities included in warnings are Raleigh, Charlotte, Louisville, Nashville, Memphis and Little Rock.

Snow had already developed over parts of the central Plains Wednesday night and Thursday morning. The National Weather Service has posted winter storm warnings and winter weather advisories for parts of Nebraska, Kansas, Missouri, far northeastern Oklahoma and Arkansas.

This snow will gradually taper off during the day on Thursday, giving way to an area of low pressure that will develop over the Lower Mississippi Valley Thursday night. On the warm side of Winter Storm Jonas, scattered severe thunderstorms, including a few tornadoes, may impact parts of the Gulf Coast states and Florida through Friday.

(MORE: Science Behind Naming Winter Storms)

Let's start with the impacts from Jonas, then we'll detail the forecast timing.

Snow and Ice Impacts

• At least 1 foot of snow likely: Eastern Kentucky into most of West Virginia, Virginia except southeast portion, most of Maryland, D.C., northern Delaware, far southern Pennsylvania and extreme northwest North Carolina. Parts of these areas may see more than 20 inches of total snowfall.
• At least 6 inches of snow likely: I-95 corridor northward through New York City/Long Island, westward into the Ohio Valley and northwest Tennessee. 
• Sharp snowfall gradient: There remains considerable uncertainty regarding snow amounts on the northern edge of Jonas' snow shield from Pennsylvania to southern New England. These areas could see snowfall exceeding 6 inches, but confidence is not as high as areas just to the south.
• Ice: The highest probability of accumulating ice to the extent of not only leading to slick roads, but also some tree damage and power outages, includes parts of central and eastern Kentucky, northern South Carolina and western and central North Carolina. Lighter ice accumulation may still lead to slick roads from eastern Arkansas to southern Virginia.

High Winds

• Strongest wind potential: Delmarva Peninsula, Chesapeake Bay, New Jersey and Long Island Saturday. Occasional gusts to 60 mph, coupled with the weight of wet, heavy snow in some of these areas, will likely lead to power outages, downed trees and limbs, and perhaps some structural damage.
• Additional strong gusts: Washington and Baltimore metropolitan areas, where blizzard conditions are possible; New England coast, particularly southeast New England, Cape Cod, Nantucket Island and Martha's Vineyard; North Carolina's Outer Banks. There will also be rather strong winds gusts in the Mid-South region of west Tennessee, southeast Missouri, eastern Arkansas and northwest Mississippi Friday that could also produce local blizzard conditions in spots. The combination of heavy snow and these strong winds could lead to power outages and some downed trees/limbs.

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Coastal Flooding

There remains some uncertainty regarding coastal flood impacts, as, once again, the exact track and forward speed of the low-pressure center will dictate wind direction, wind duration and the length of the wind flow over water, or fetch, all components to determining the amount of coastal surge flooding and battering waves atop the surge.

With a full moon this weekend, tides will already be running high, which could worsen coastal flooding impacts, as strong winds drive onshore during multiple tide cycles.

Areas of particular concern according to the National Weather Service include:

• Delaware, including both Delaware Bay and the Atlantic beaches, southward to Maryland's Atlantic coast
• The Jersey shore, including the south shore of Raritan Bay
• The western side of Chesapeake Bay, including tidewater inlets and the Norfolk/Newport News metropolitan area

(INTERACTIVE: Coastal Flood/Marine Alerts)

In these areas, major coastal flooding is possible for both Saturday morning and Saturday evening high tides, with potential beach erosion and even property damage.

Other areas with a chance of moderate coastal flooding include the west end of Long Island Sound, the south shore of Massachusetts, Cape Cod, Martha's Vineyard and Nantucket Island.

For more on the threat of coastal flooding and strong winds, see our full article at this link.

Winter Storm Jonas: Timing

• Thursday/Thursday night: Light snow in the central and northern Plains, with some sleet and freezing rain in the Mid-South region. By Thursday night, the Plains snow diminishes, while a broad stripe of snow, sleet and/or freezing rain develops from the Ark-La-Tex region into Kentucky, the Appalachians and adjacent Piedmont of Virginia and North Carolina.

• Friday/Friday night: Rain changes to snow in the Tennessee Valley and the Mid-South. A mess of snow, sleet or freezing rain spreads into the lower Ohio Valley, Appalachians, Carolinas and Virginia. Snow spreads north up the Interstate 95 corridor Friday afternoon and Friday night mainly south of New York City. Winds intensify Friday night along the coast from the Carolinas to the Jersey Shore, and near Chesapeake Bay.

• Saturday/Saturday night: Heavy snow in the Appalachians and parts of the Mid-Atlantic states, with some sleet/freezing rain mixed in at times. Snow will spread into southern New England. Precipitation may change to snow as far south as parts of South Carolina. Rain changes to snow near the Mid-Atlantic coast. Strong, possibly damaging winds from the Delmarva Peninsula to Cape Cod.

• Sunday: Snow and strong winds diminish along the Mid-Atlantic Seaboard, but may linger a bit longer in coastal southeast New England. 

(FORECAST: Louisville, Kentucky | Roanoke, Virginia | Greensboro, North Carolina)

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