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Key points:

  • Snow totals have mainly reached 10-14 inches south and southeast of the District, 14-22 inches inside the Beltway and to the northeast, and 20-30 inches west, north, and northwest of the Beltway.
  • Snowfall rates up to 2 inches per hour are possible into the early evening, easing a bit thereafter.
  • Wind gusts of 30-40 mph cause near whiteout conditions with blowing and drifting snow.
  • Total snow accumulations of 16 to 30 inches are expected with some 30-36 inch totals well north and west of the District (Frederick and Loudoun counties). 20-30 inches totals will be most common in the immediate metro region. Totals in the 12-20 inch range are most likely near the Bay into Southern Maryland.

We have a new live update post — please follow this link for the latest information

The massive winter storm pounding the East Coast is set to surpass 2010's 'Snowmageddon' in total snowfall. Capital Weather Gang's Angela Fritz has your forecast and snow accumulation predictions. (Ashleigh Joplin,Angela Fritz/The Washington Post)

2:03 p.m. update: Snowfall rates are up again across the immediate metro, and we expect that to continue for the rest of the afternoon. If things continue like this, we could see another 4 to 6 inches in the Beltway by the time this storm is over.


1:37 p.m. update: The National Weather Service thinks that 14.9 inches at National is legit. They just saw much less snow than the rest of the region — even downtown. We’re watching rates pick up again across the Beltway now as the dry slot fills in.

1:22 p.m. update: The official observation from National at 1 p.m. was 14.9 inches — which means only 0.9 inches fell in six hours. It’s true that we’ve been in a dry slot for most of the day so far, but this still seems a little low to us. We weren’t expecting a huge total, but another 1.5-2 inches or so.

Folks around National — does ~15 inches sound about right to you based on what you’ve measured?

At Dulles, the 1 p.m. report was 23.5 inches.

1:11 p.m. update: The HRRR shows 8 inches of snow falling at National after 11 a.m. While the model didn’t resolve the extent of the dry slot, it did catch on that snowfall rates were decreased in areas around and southeast of the Beltway. So if the HRRR is right (which we don’t really think it is) then that puts National at around 22 inches for storm total snowfall, likely an over-estimate.

We do think it’s interesting that most of those 8 inches falls after 2 p.m. — so it at least got that right. But since it didn’t catch on to the dry slot, we can’t hang out hats on this guidance. We also don’t think the snow totals are high enough for the northwest suburbs.


(weatherbell.com)

12:50 p.m. update: Snowfall totals from the “crush zone” northwest of the city, with much more to come!

3 miles southwest of Frederick, Md. — 36 inches
Derwood, Md. — 20 inches
Winchester, Va. — 29 inches
Sterling, Va. — 26 inches
Leesburg, Va. — 26 inches
Haymarket, Va. — 28 inches

12:20 p.m. update: Looking at radar, we could see snowfall rates begin to pick up around the Beltway and in areas south and east of the city soon. It looks like new convection is developing in the dry slot, acting to fill in that gap and put an end to the low snowfall rates that these areas have seen over the past couple of hours.


12:13 p.m. update: Winds continue to gust hard across the region.

At 12 p.m., National was reporting gusts up to 36 mph, Dulles up to 33 mph, and BWI up to 32 mph. The HRRR model suggests peak winds will continue through the mid to late afternoon, shown below in knots at 4 p.m.


(weatherbell.com)

12:05 p.m. update: Lots of people out near the Capitol this morning, celebrating the fact that they are indeed allowed to sled there without risk of arrest.

Details on the lifting of the sledding ban from PowerPost:

Buried deep in the drifts of the $1.1 trillion spending deal approved last month was a line directing the U.S. Capitol Police to ease up on an official ban and allow the city’s iconic hill to once again serve as a snowy sledding slope.

Last year area parents organized sled-in protests after Capitol Police Board Chairman Frank Larkin announced that after years of turning a blind eye, officers would enforce the ban for “security reasons.”

Larkin said his hands were tied and it would take an act of Congress to grease the skids. District Del. Eleanor Holmes Norton worked with California Democrat Sam Farr to make sure the issue was resolved through the appropriations process.

The legislation instructs the Capitol Police to “forbear enforcement” of a 1963 ban intended to “protect the public property, turf and grass of Capitol Grounds from injury.”

When translated from Congress-speak that means the grounds are again fair game for residents looking for a little fun during the upcoming snowfall.

11:47 a.m. update: The storm’s so-called comma head, where heavy snow bands set up and remain stationary for hours, has become established north and west of the Beltway. The areas in this zone are likely to receive over 2 feet of snow (some already have), and possibly up to 3 feet, especially at higher elevations.

This zone includes Winchester, Front Royal, Gaithersburg, Damascus, Sterling, Leesburg, Hagerstown and Frederick.

Radar at 11:30 a.m.:

radar

Satellite, showing comma head dropping west of I-95:

sat

11:35 a.m. update: Angela Fritz and video producer Ashleigh Joplin went outside so you don’t have to! Here’s what to expect through the afternoon.

Capital Weather Gang's Angela Fritz takes snow accumulation measurements from downtown D.C. and makes predictions for the potentially historic blizzard hitting the Washington area and the mid-Atlantic. (Ashleigh Joplin,Angela Fritz/The Washington Post)

11:30 a.m. update: Snowfall rates have dropped dramatically in the Beltway and locations south and southeast of the city. You can see why this is on the radar — we’re getting dry-slotted. Areas to the north and west of the city are seeing much heavier snowfall rates, which are shown in the rich blue color.

This is NOT a bust for D.C., because it’s still snowing and we’ll still see some higher snowfall rates later today.


10:50 a.m. update: A fresh look at snowfall totals from the National Weather Service and our readers, now mainly in the 14-20″ range…

Reagan National: 14.8″
Dulles Airport: 23.4″
Chevy Chase: 17″
Alexandria: 17″
Annandale: 15.5″
Lincoln Park (D.C.): 14″
Annapolis: 14″
Fairfax: 16″
Navy Yard: 16″
Olney: 18″
McLean: 16″
Sterling: 20″
Rockville: 19.5″
Darnestown: 23″
Aspen Hill: 19″
Leesburg: 20.5″
Gaitherburg: 21″
Manassas: 24″

10:30 a.m. update: Looking at the latest model data, it appears the northwest suburbs are going to continue to get hammered with snow through around 2 p.m., while snow continues slower but still steady elsewhere. The expected snow intensity can best be inferred from model forecasts of vertical velocities (up and down motions) in the atmosphere. The graphic immediately below from the NAM model shows what the vertical velocities were expected to be at 10 a.m. Those reds and purples north and west of D.C. are *really* intense, with snowfall rates likely around 2 inches per hour. The graphic below that shows the forecast at 4 p.m., when the intensity has decreased but is still fairly solid across a broad portion of the area.

NAM vertical velocity forecast for 10 a.m. today.
NAM vertical velocity forecast for 10 a.m. today. (College of DuPage)
NAM vertical velocity forecast for 4 p.m. today. (College of DuPage)
NAM vertical velocity forecast for 4 p.m. today. (College of DuPage)

10:15 a.m. update: How about the wind? Wind gusts have generally been in the 25-45 mph range locally. They’ll probably go up a bit as we get into the late morning and afternoon, maxing out around 30-50 mph, but with the potential for locally stronger gusts, especially east of D.C. and I-95. So far power outages are only in the hundreds locally, much better than the thousands and tens of thousands that were possible. That could change as the snow continues to pile up and winds increase bit. But for now this is good news. Meanwhile, check out the raging winds on the Eastern Shore…

9:50 a.m. update: From the National Weather Service, for D.C./I-95 and points north and west through midday and beyond:
PEAK SNOW RATES WITHIN THIS CORRIDOR WILL LOCALLY EXCEED 2 IN/HR…WITH BLIZZARD OR NEAR-BLIZZARD CONDITIONS CONTINUING PARTICULARLY IN AREAS NEAR/JUST WEST OF THE I-95 CORRIDOR

9:45 a.m. update: OK, this is cool…

9:25 a.m. update: Is this thing officially a blizzard yet? According to National Weather Service blizzard warning criteria which we detailed earlier, Snowzilla is close to a blizzard as measured at Dulles Airport, but maybe not quite there. It may still be considered just short as one of the criteria is frequent wind gusts of 35 mph or greater. The last three hourly wind gust observations (31, 28, and 46 mph) average out to 35 mph, but obviously are not all 35 mph or greater. The other criteria — heavy snow and visibilities of 0.25 miles — have been met in each of the last three hours.

9:05 a.m. update: Here’s what we think is a more realistic forecast (from the NAM model) of snowfall from 7 a.m. this morning through 1 a.m. tonight, by when the accumulating snow should be over or just about done. While it’s not so easy to match the colors with the legend, it generally indicates 10-14″ in the metro area (highest north and west, lowest south and east). This may still be a few inches too high, especially from D.C./I-95 and to the south and east where we will see periods of lighter snow and maybe some sleet. But even if you only add 6-12″ to the 12-18″ many places had as of early this morning, that gets us into the 18-30″ across the area.


NAM model snow accumulation forecast for 7 a.m. today through 1 a.m. tonight.

8:45 a.m. update: As we await the latest model data to get a better idea on how much snow is left to go (we think we’re still on track for generally 16-30″, we’re on the lookout for official blizzard conditions, which require “snow and/or blowing snow reducing visibility to 1/4 mile or less for 3 hours or longer AND sustained winds of 35 mph or greater or frequent gusts to 35 mph or greater” according to the National Weather Service. The criteria has not yet been met at National, Dulles or BWI. Although Dulles did report a wind gust of 46 mph earlier this morning and six consecutive hours of quarter-mile visibility. The winds are really ripping at the beaches where flooding is occurring in Ocean City…

8:25 a.m. update: How much more snow? The short-range HRRR model below shows around 20 inches falling across the immediate metro area between 6 a.m. and 4 p.m. today (on top of what fell yesterday afternoon and overnight). An image like this is what we like to call “weather porn.” It is likely quite exaggerated. We’ll be back shortly with a more realistic estimate.


HRRR model snowfall forecast for 6 a.m. to 4 p.m. today.

8:00 a.m. update: North and west of D.C. and I-95, the snow continues steady and heavy at times at the moment, and that should continue to be the case throughout the day. As we discussed below, an anticipated dry slot with lighter precipitation has moved into areas from D.C. and toward the south and east. So for those of you in the District, Prince George’s, Anne Arundel, Charles and Stafford counties and toward points south and east, you may be in and out of lighter snow (with possible some sleet mixed in) before steadier and heavier snow likely picks up again during the afternoon. The NAM high-resolution radar simulation for 5 a.m. today through 4 a.m. tomorrow depicts this well…


NAM model high-resolution simulated radar forecast for 5 a.m. today through 4 a.m. tomorrow.

7:30 a.m. update: How much snow so far? Snow totals so far compiled from National Weather Service and reader reports. The 14″ at National as of 7 a.m. is just a few inches short of entering the top five for D.C. storms and already ranks the 12th biggest (see Top 25 D.C. snowstorms)

Reagan National: 14″ (official airport observer)
Dulles Airport: 15.2″
BWI Airport: 12.4″
Damascus: 18″
Germantown: 16″
Columbia Heights: 11″
Falls Church: 16″
Bethesda: 15″
Reston: 16″
Chantilly: 16″
Petworth: 14.5″
Waldorf: 13.1″
Frederick, Md: 17″
Alexandria: 15″
Fairfax Station: 16.5″

7:10 a.m. update: A dry slot in the precipitation working toward D.C. from the southeast was not unexpected, and in fact why snow total forecasts are lowest south and east of D.C. and I-95. It is this area where we may see a lull in the snow at times (and/or mixing with sleet) through this morning. Although as the whole storm pivots counterclockwise and then starts to pull to the east-northeast, that lull will likely fill in again during the afternoon into evening.

A NASA Center for Climate Simulation supercomputer model shows the flow of the massive snow storm over the East Coast through Sunday, Jan. 24. (YouTube/Nasa.gov Video)

6:45 a.m. update: Take a look at the current radar image below and get used to it. The yellow blob indicates intense snow and is likely to focus on that same area just north and west of D.C. through much of the day. Somewhere in it we may see totals approach 30″.

Radar at 6:39 a.m. (Weather Underground)
Radar at 6:39 a.m. (Weather Underground)

6:25 a.m. update: Thundersnow! No doubt about it. Numerous reports of it coming in from across a large area at around 6:15 a.m. as Snowzilla continues to amaze. With the overnight snow accumulations are reported generally in the 12-18″ range across the area (highest north and west, lowest south and east).

A Capitol size snow clean-up this morning. (Ashley Sinha via Twitter)
A Capitol size snow clean-up this morning. (Ashley Sinha via Twitter)