Capital Weather Gang's Jason Samenow has the latest on what we can expect from this week's winter storm. (Monica Akhtar,Jason Samenow/The Washington Post)

*  Winter storm warning for areas along and west of Interstate 95 in D.C. area, including the District, 7 p.m. Monday to 2  p.m. Tuesday | Winter storm watch for Stafford, Prince George’s and Anne Arundel counties *

(This post, originally posted at 11:50 a.m., was updated at 2 p.m., 3 p.m. and 6:00 p.m.)

A powerful Nor’easter will roar up the Mid-Atlantic and Northeast coasts Monday night and Tuesday, unleashing heavy snow and howling winds, and flooding some coastal areas. Snowfall totals may vary widely in the Washington region, with amounts exceeding 8 inches a good possibility just north of the city, but as low as two inches in southeastern suburbs. Inside the Beltway, 4 to 8 inches is most likely.

Up and down the Interstate 95 corridor, the storm will hit fast but hard. In just 12 hours, it could generate historic snowfall amounts for March in some areas.

The snow amount forecast in Washington is still quite uncertain, as the region is predicted to lie on the edge of the storm’s sweet spot, and slight changes in how it develops and moves could be the difference between a bust and a blockbuster. The main American forecast model, the GFS, forecasts a large amount of snow for Washington, while the European model – which is the highest performing – suggests a much lower impact event because of rain mixing in.


A March snowstorm is rare, but not unprecedented in the D.C. region. (Claritza Jimenez/The Washington Post)

Snow in Washington is expected to begin between 5 and 8 p.m. Monday and should taper off Tuesday morning. Rain and sleet could mix with the snow, especially east and southeast of the Beltway, which would limit amounts. The snow and mixed precipitation could fall very heavily for a time late Monday night, with snowfall rates in excess of one to two inches per hour. School and office closures are quite possible on Tuesday, especially west of Interstate 95.

The highest confidence for heavy snowfall in the Washington area is in northern Fauquier, Loudoun, northern Montgomery, northwestern Howard, and Frederick counties; confidence in snowfall amounts of five inches or more decrease as you head south and east of there. The National Weather Service has posted winter storm warnings for areas along and west of I-95, including the District, where such amounts are considered to have at least a 50 percent likelihood.


National Weather Service snowfall forecast for D.C.

Snow that falls in portions of the Washington area could be heavy and wet. The weight of the snow on power lines and tree branches, some of which have begun to flower and leaf, along with top wind gusts to 25 to 30 mph, could lead to power outages in portions of the region.

(Programming note: Capital Weather Gang will live blog the latest model forecasts for this storm on Sunday evening starting around at 10 p.m. at washingtonpost.com/capitalweathergang)

The storm will be particularly severe from New York City to Boston, which will be hit by a punishing combination of very heavy snow and strong winds very late Monday night into Tuesday. Blizzard watches have been posted for this area as travel could be made impossible because of snowfall amounts of 12 to 18 inches and wind gusts over 50 mph. The snowfall rates could exceed three inches per hour at times in this zone, with the possibility of thundersnow. The brunt of the storm will hit New York City from roughly 4 a.m. to 4 p.m. Tuesday and Boston from about 8 a.m. to 8 p.m.


National Weather Service forecast snow totals Monday night to Tuesday night. (WeatherBell.com)

In the Mid-Atlantic and Northeast, more than 50 million people are under winter storm or blizzard watches and/or warnings.

The storm will generate large waves and a powerful tidal surge that will batter the Atlantic beaches, particularly in eastern New England. In eastern Massachusetts on Tuesday and Tuesday night, the storm “has the potential to wreak havoc on the coastline given a potential for 2 to 3 foot storm surges and waves in excess of 20 feet just offshore” the Weather Service forecast office serving Boston said. Farther south into the Delmarva, some minor coastal flooding is possible around high tide Tuesday morning.


GFS model simulation of the winter storm Monday to Tuesday night.

The power of the storm is tied to the merger of two flows of energy off the Mid-Atlantic coast, one originating from Canada and a second from the Gulf of Mexico.

The storm will fall on the 24th anniversary of the “Blizzard of 93,” the most extreme March storm to hit the East Coast in recorded history. While it won’t be that strong, Monday night’s storm is forecast to explosively intensify or “bomb out” as it charges up the coast, much like that 1993 storm.

Washington region forecast details

While forecast confidence for heavy snow is highest around New York City and Boston, a very disruptive, heavy snowfall is possible in Washington if everything comes together just right. A number of forecast models have shown the immediate D.C. area getting buried by snowfall amounts into the double digits.


The GFS model snowfall forecast is a top-end scenario for the D.C. region if all ingredients for snow came together. (StormVistaWxModels.com)

But others have the region right along the edge of where significant snow starts and stops and suggest the possibility of just a slushy, relatively inconsequential accumulation — especially near the Beltway and to the east and south.


NAM model total snowfall forecast … shows lower-end totals inside the Beltway and to the southeast. (StormVistaWxModels.com)

“The uncertainty about the storm track makes the snow accumulation forecasts lower confidence ones than with many of our strong Nor’easters,” said Wes Junker, Capital Weather Gang’s winter weather expert.

The forecast for snowfall in the Washington area is especially challenging for three main reasons:

1) The D.C. region looks to be on the southern edge of the heaviest precipitation. The edge of a heavy precipitation area is always trickiest to forecast because a slight shift could make the difference between missing the heavy precipitation or getting hammered.

In this storm, if the heaviest precipitation just misses Washington to the north and northeast, it would not only reduce the amount of snow we get, but it also would increase temperatures some — which would make it more difficult for the snow that does fall to accumulate.

If this storm rapidly develops and produces the heavy amounts of precipitation some models are suggesting, widespread double-digit snow totals would be possible, even in the immediate area. But if the storm is slow to develop and doesn’t really get its act together until it’s north of D.C., snowfall amounts could be significantly less than forecast.

2) Parts of the D.C. area are likely to straddle the rain-snow line, which is a moving target. Depending on how close the storm tracks to the coast and how fast the storm develops (as discussed above), enough mild air may hang around or be drawn inland from the ocean so that some precipitation falls as rain or sleet, especially from Interstate 95 and eastward. Obviously, in areas where rain and sleet fall, snow totals will be limited.

Most models keep the rain-snow line southeast of Interstate 95 in Southern Maryland, but there have been some model forecasts that sneak the rain-snow line northwestward into the immediate area. We could see that scenario unfold if the storm tracks close to the coast or just inland and/or is slow to develop. If the rain-snow line ends up near Interstate 95, it would result in “bust scenario” snowfall totals.

3) Temperatures. When precipitation first arrives in the D.C. region Monday evening, temperatures in most locations will be well above freezing. They are forecast to steadily drop, but, for snow to accumulate, they will need to drop a good deal — especially around the city.

The European model actually keeps temperatures in Washington and to the east and southeast just above freezing for most of the storm. Sometimes this model doesn’t cool temperatures down enough in situations like this, and other models are colder. Also, if it’s 33 or 34 degrees and snowing heavily, as the European model suggests, the snow can still accumulate — though not as fast.


The European model simulation of temperatures at 2 a.m. Tuesday. Temperatures are around 33 degrees in Washington. (StormVistaWxModels.com)

We will need to watch temperatures and temperature forecasts carefully. If they are a little warmer than we’re expecting, the snow we’re calling for will not materialize, especially inside the Beltway and south and east. On the other hand, if they are on the cold side of model predictions, the snow will really pile up.


The GFS model shows temperatures around 30 degrees at 2 a.m. Tuesday morning.

We hope to gain a little more forecast confidence this evening and will have a live blogging session beginning around 10 p.m. (because of the switch to daylight saving time, models come in an hour later, unfortunately). Also, refresh this post throughout the day as we will update and revise it some as new information comes in.