Key points

Snow gave way to freezing rain and sleet this afternoon and evening. Untreated roads and sidewalks have become dangerously treacherous.

Temperatures may not rise above freezing many places until ~4-6 a.m. Even with rapid warming thereafter, icy spots may linger until ~7 a.m. (perhaps even ~9 a.m. in the outer north and west suburbs).

Heavy rain – around an inch – is likely during the day Tuesday, and flooding of streams/creeks and power drainage areas is possible. Temps will spike to near 50 or even higher in some areas.

Snowfall totals were generally in the 3-5 inch range, but up to 5-9 inches fell in parts of our south and southeast suburbs (“boom” scenario) and less far north, northeast and northwest — closer to 2-4 inches.

Updates

11:20 p.m. update: OK we lied. One more update. First, we should mention there is the possibility of thunder with Tuesday morning’s heavy rain. Second, the latest HRRR model has Tuesday lunchtime temperatures in D.C. near 60! Now that may be overdone, but anything’s possible with such a dynamic storm system.

10:45 p.m. update: Well, there’s not much else to say at this point in the evening. Please stay off the roads overnight, and check with us here on the blog, and on Twitter and Facebook, early in the morning for the latest conditions and forecast. See immediately below for our best guess on conditions for the morning commute, and see earlier updates below for a detailed look at the expected arrival timeline for above-freezing temperatures late tonight into the early morning.

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10:15 p.m. update: Now that we’ve timed-out the expected arrival of above-freezing temperatures from southeast to northwest across the area (see earlier updates on this below), let’s discuss what it all means for the morning commute. While most spots should be above freezing by around 5 a.m., except perhaps the outer north and west suburbs, readings are still likely to be in the 30s at that time, which is probably cold enough for numerous icy spots to linger. May take until ~7 a.m. to melt off all the slick spots, and perhaps even until ~9 a.m. in our far northern and western areas (e.g., Frederick, Loudoun and Fauquier counties).

Complicating things, remember we are expecting moderate to heavy rain to move in prior to or during the commute.

9:35 p.m. update After taking until approximately 4-6 a.m. for most of the area to have climbed above freezing (see earlier updates below for the expected transition timeline from southeast to northwest), the latest HRRR model shows how quickly temperatures warm thereafter. It shows the 40s having reached all the way into Frederick, Loudoun and Fauquier counties, with areas near and inside the Beltway approaching or reaching the 50-degree mark. That’s about as warm as we’ll get, though, and in fact temperatures may fall back into the 40s toward lunchtime. (Update 11:10 p.m.: The latest modeling delays the cooling until the afternoon, and even has lunchtime temperatures in D.C reaching near 60. This may be overdone, but anything’s possible with such a dynamic storm system.)

9:10 p.m. update: Hopefully everyone has made the right decision to stay home this evening. Because this is a terrible batch of freezing rain and sleet now moving through, especially from D.C. to the west.

http://twitter.com/mikepesce/status/699408439173373952

8:50 p.m. update: Continuing our look at the expected transition of above-freezing temperatures from southeast to northwest, by around 7 a.m. our best model for short-range (0-15 hours) temperature forecasts shows the 32F line having advanced rapidly to the northwest all the way into Western Maryland and West Virginia. Meanwhile note how 50s have reached to just southeast of D.C.

8:15 p.m. update: Current temperatures remain locked in the mid-20s to near 30 across the entire metro area with scattered areas of freezing rain and a bit of sleet continuing to move through. Treated main roads are probably doing O.K. But now with daylight long gone, a DANGEROUSLY sick glaze has solidified on many sidewalks and increasingly on secondary and neighborhood roads as well. With that Metro has suspended bus service starting at 10 p.m.

7:50 p.m. update: Two updates below we showed the expected northwestward progress of above-freezing temperatures by 4 a.m. By that time, or perhaps an hour or so earlier, the northwestward progress of the above-freezing line should be accelerating, such that by 5 a.m. (just an hour later) our go-to model for short-range temperature forecasts has most of Howard, Montgomery, Prince William and all of Fairfax counties above freezing. I think this may be an hour or two too slow, but not impossible that it takes until then.

7:30 p.m. update: The winter storm warning is now cancelled for D.C., Arlington, Falls Church, Alexandria and Prince George’s, Charles, St. Mary’s and Calvert counties. It is replaced by a winter weather advisory — for light amounts of sleet and around one-tenth of an inch of ice from freezing rain — that covers D.C. and Howard, Montgomery, Prince George’s and Charles counties and points east until 10 a.m. Tuesday.

7:10 p.m. update: We’re looking at when temperatures are expected to rise above freezing tonight from southeast to northwest. As seen below, our typically best model for short-range temperature forecasting has above-freezing temperatures reaching just past D.C. and I-95 by 4 a.m. This may be a worst-case scenario (but perfectly plausible) as I wouldn’t be surprised if it’s an hour or two earlier. In our next update we’ll look at the timing for the north and west suburbs.

6:40 p.m. update: Let’s take a look at when we expect temperatures to rise above freezing by zone. As above-freezing temperatures work their way from southeast to northwest, Southern Maryland will be the first to rise above 32F by around 2 a.m. tonight as seen below. So says the HRRR model, which is our go-to model for short-term temperature forecasts (and usually quite good).

6:05 p.m. update: Temperatures remain quite chilly early this evening. There are growing signs of above freezing air gathering over southern Maryland and nearer the ocean, but spots locally remain locked in the 20s to near 30.

CWG’s Jeff Halverson points out that recent weather analyses show a small area of weak low pressure that has developed near the mouth of the bay.

This feature may help the cold air linger by keeping winds from coming out of warm directions, at least for now. Eventually, the developing storm over Alabama — and warmer winds ahead of it — works close enough to the region that it should overpower the little coastal low. Recent short-term modeling keeps the whole area near or below freezing until near or after midnight. It then rapidly warms everyone above freezing into sunrise.

5:45 p.m. update: Going wider again, we see this storm system is quite sprawling. Today’s snow activity has moved north of the area, and lots of moisture is gathering to the southwest. A low pressure system forming down in Alabama has caused severe weather across the Gulf Coast region this afternoon. A number of reports of tornadoes have come in from that region.

The wider radar view shows that precipitation targeting this area remains mostly showery to the south. There’s some model indication this may congeal into a uniform zone of freezing rain and rain as it moves toward us from the Carolinas this evening and overnight, but that’s not a guarantee.

5:25 p.m. update: Much of the steady precipitation has moved north of the area. For the next few hours at least, it should tend to be more spotty and showery, although freezing drizzle is possible in the lulls. A radar snapshot early this evening shows that well. Although many spots have turned over to freezing rain, some sleet may fall in heavier activity.

5:05 p.m. update: We haven’t focused on tomorrow much, but it also promises to be an active day. A flood watch is in effect across the region as heavy rain is possible (around one inch) as temperatures rise to 50 degrees or so. All this means we’re going to have a rapid snow and ice melt and heavy rain falling at the same time. Streams and creeks as well as poor drainage areas are at risk of flooding. The heaviest rain is likely in the morning between rush hour and midday.

4:40 p.m. update: With the loss of daylight, untreated roads and sidewalks – currently being glazed by light freezing rain – will become especially treacherous. Ice accumulates much more readily at night compared to during the day. Be extremely careful as surfaces transition from slushy to downright slick.

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4:35 p.m. update: In case you’re interested, we’ve posted SchoolCast and FedCast.

3:50 p.m. update: The freezing rain line is racing north and is now through much of the area. Some of the far northern suburbs in places like Frederick County are still seeing snow before the changeover.

A consistent area of freezing rain will move through over the next hour or two, before it turns a bit more showery at least for a time. Use extra caution as the ice glaze builds.

3:20 p.m. update: A wide view of this storm system shows we’ve got awhile to go. Temperatures are slowly rising through the 20s to around 30 locally and snow is changing to freezing rain across the region.

There’s still no apparent warm push targeting the area, but temperatures will continue to slowly rise through the evening. As low pressure organizes to the south, we’ll eventually see a more significant rise overnight toward morning. One potential positive is that precipitation seems to want to be somewhat showery in the time ahead, which may be able to limit ice accumulation, at least in spots.

2:55 p.m. update: As the next area of precipitation pushes in, reports and radar tend to indicate the snow is done except for perhaps a few intermixed flakes. Going straight to sleet and quickly to freezing rain appears to be the story. An icy glaze is likely to develop on all untreated surfaces in the hours ahead.

2:35 p.m. update: As we await the next batch of precipitation, now on our doorstep to the south, some more snow photos.

2:05 p.m. update: The Storm Prediction Center is highlighting the area for a change to freezing rain in the period ahead.

It’s a technical discussion, but the key snippets tell the story. The change to sleet, probably quickly to freezing rain, is just to the south of D.C. now, and should race toward the Maryland/Pennsylvania border over the next few hours.

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WINTER MIXED PRECIPITATION WILL CONTINUE TO ADVANCE NORTHWARD ACROSS THE MID-ATLANTIC REGION. A TRANSITION FROM SNOW TO A PERIOD OF SLEET TO THEN FREEZING RAIN WILL OCCUR THROUGH THIS AFTERNOON AND INTO THIS EVENING. FREEZING RAIN RATES UP TO SEVERAL HUNDREDTHS OF AN INCH PER HOUR WILL BE POSSIBLE. .. EASTERN PORTIONS OF THIS TRANSITION ZONE WILL ADVANCE MORE RAPIDLY N/NW OVER THE NEXT FEW HOURS…WITH FREEZING RAIN LIKELY OVERSPREADING THE I-95 CORRIDOR FROM DC TO NYC OVER THE NEXT FEW HOURS.

1:45 p.m. update: New snow reports are in from the NWS. Below is a selected list of some of the totals through early afternoon. In general, the highest numbers are across parts of southern Maryland and into central Virginia. The lowest numbers are north and well west of the city. Backward from the typical around here!

California, Md. — 8.5″

Dentsville, Md. — 7.7″

Prince Frederick, Md. — 6.1″

Burke, Va. — 6.0″

Fredericksburg, Va. — 6.0″

Staunton, Va. — 4.5″

Oxon Hill, Md. — 4.3″

Takoma Park, Md. — 4.0″

Fairfax, Va. — 3.0″

Leesburg, Va. — 3.0″

National Airport, Va. — 2.6″

Simpsonville, Md. — 2.5″

Dulles Airport, Va. — 2.2″

BWI Airport, Md. — 2.0″

1:25 p.m. update: It’s still quite cold this afternoon. At 1 p.m., it was 27 at National Airport and 24 at Dulles. Even down toward Richmond, it was 27.

High-resolution models show mostly below freezing temperatures deep into the evening, with the I-95 corridor rising near and above freezing around midnight. Something to watch as this would be on the late side of anticipated. It’s worth noting it seems a little cold to start, and slow to move temperatures.

1:00 p.m. update: To shovel now or wait?

It can’t hurt to do it now given the snow remains fluffy and easy to move, but you may want to not clear to bare pavement unless using an ice melter. There is still some question as to exactly when everyone rises above freezing this evening and tonight, even in the city. The longer the area sees mixed precipitation and freezing rain, the more solidified (and heavy) this snow will become. Even with temperatures rising well above freezing into tomorrow, it may prove difficult to melt and move.

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12:40 p.m. update: CWG’s Angela Fritz has a full update on the storm impacting the region, including what we can expect tonight into tomorrow.

And check out the beautiful scenes of today’s holiday snow in the city.

12:35 p.m. update: Area dogs and cats always seem to enjoy the snowfall, either outdoors or in!

12:10 p.m. update: Places to the south like Richmond have changed over to sleet. It looks like the next batch arriving in a few hours will change rather quickly from snow to sleet and eventually freezing rain. A brief burst of snow is possible as it arrives. The most recent HRRR model run still focuses on around 3 p.m. for the changeover in the city, but temperatures remain below freezing into evening.

11:50 a.m. update: For the most part, snowfall intensity has dwindled lately. There are still some moderate bursts intermixed. A lull between this morning’s snowfall and the next batch of precipitation is working this way from the south.

We should tend to see snowfall rates continue to diminish in the hour ahead (a little longer well north of the city), and it might even stop for a time. The lull could be rather short lived as the next batch moves this way from roughly a Charlottesville to Richmond line. Some showery snowfall is ongoing in the lull area as well. Mixing with sleet and eventually freezing rain will likely come with the next batch as we head through the afternoon.

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11:30 a.m. update: Word of many delays and cancellations at area airports continues to pour in. National Airport (DCA) remains open, but there are temporary stoppages for plowing the runways.

11:15 a.m. update: This has been a peaceful snowfall across the area without too much wind. Add in cold temperatures helping the fluff factor, and it’s quite photogenic. A small sample of the scenes across the area late this morning:

10:45 a.m. update: Here’s a quick round-up of snowfall totals as of about 10:30 a.m. Generally, we have 2-4 inches inside the Beltway, and more as you go south and southeast (5-9 inches) and less in our far western and northern areas (1-2 inches).

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Some specific totals:

The District: 2-3″

Virginia: Arlington 3-3.5″, Alexandria 3-4″, Oakton 2.5″, Reston 3-3.5″, Falls Church 3.5″, Springfield 4″, Manassas 4″, Fairfax 3-3.5″, Annandale 4″, Brambleton 2″

Maryland: Olney 2″, Silver Spring 2″, Columbia 2″, Rockville 2″, Gaithersburg 2.5″, Severna Park 2.5″, Laurel 1.5-2″

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The boom zone: LaPlata, Md. 6″; Lusby, Md. 6″; Stafford, Va. 7″; St. Leonard, Md. 7″; Dumfries, Va. 5″; Charlotte Hall, Md. 8″; 7″ Lexington Park, Md., 7″ Patuxent River, Md., King George, Va. 8″

The bust zone: Frederick, Md. 1″; Front Royal, Va. 1.7″; Western Loudoun Co., Va. 2″

10:10 a.m. update: One of the challenging aspects of this forecast is the timing of the changeover to snow to sleet and freezing rain. One of our short-range models, known as the HRRR, predicts it will occur between about 2 and 4 p.m., pushing through the region from southeast to northwest. Here’s a simulation showing the snow-mix line cutting through D.C. at 3 p.m.

The changeover timing is consistent with other models like the NAM and SREF.

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The National Weather Service posted an analysis showing the mix line near Richmond around 9:45 a.m., pushing northwest.

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The practical implications of the changeover means accumulating snow will stop, and ice accumulation will commence of up to a few hundredths of an inch per hour…adding a glaze on top of everything.

9:40 a.m. update: The next two to three hours are likely to present the worst of the storm in terms of accumulating snow and deteriorating road conditions. Snow should fall at a rate at about half an inch per hour, sometimes increasing to an inch per hour. We’re still anticipating a transition to mixed precipitation in the mid-to-late afternoon.

9:23 a.m. update: The National Weather Service has expanded the winter storm warning to include eastern Loudoun County, Fairfax County, the District, and Prince George’s County. Basically, much of the D.C. metro region is in a winter storm warning except our northern and northeastern suburbs, including Montgomery County, Howard County, and Anne Arundel County, which are under winter weather advisories. The expanded advisory into D.C. is due to snowfall amounts that may reach five inches along with the expected ice on top.

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8:53 a.m. update: A little on road conditions — we’re hearing and seeing that major roads are looking pretty good. The break in the snow this morning helped road crews get a jump on it, and the major thoroughfares are wet but not slippery. Side streets have a good coating of snow on them so avoid those if possible.

The only place we’ve heard things are dicey is Montgomery County, where they have a “three-inch rule.” They only put plows down if snow exceeds three inches. So we’ve heard even some of the main roads are slippery around the Rockville area.

Metro is running on time on a Saturday schedule, but bus service is running the severe plan, which means service is limited to major corridors only.

Snow is picking up across the region, so road conditions could deteriorate as we head into the late morning. If you need to get somewhere, now might be the time to leave while the roads are still in decent shape.

8:28 a.m. update: A few snow total reports from the “boom zone” down south:

Shiloh, Va. — 6.5 inches

Lusby, Md. — 6 inches

Fredericksburg, Va. — 5.5 inches

Prince Frederick, Md. — 4.2 inches

Marbury, Md. — 4.5 inches

Reports from the metro area:

Mount Vernon, Va. — 2.8 inches

Leesburg, Va. — 1 inch

Reston, Va. — 1.1 inches

Chantilly, Va. — 1.8 inches

BWI Airport — 1 inch

Columbia, Md. — 1 inch

Marlton, Md. — 2.5 inches

WBAL Baltimore City — 0.75 inches

7:53 a.m. update: Snow is spreading across the D.C. region again from south to north, and we’re getting a few reports of sleet mixed in with the snow. It’s starting out light but we expect it to get heavier over the next hour or two. The HRRR model suggests the 10 and 11 a.m. hours could bring moderately heavy snow which could lead to another inch or two of accumulation for the metro area.

7:15 a.m. update: As the sun started to come up, readers shared their snowy scenes with us. Areas to the south have seen the most snow so far this morning, while our northern suburbs have seen the least so far. We’re still in a bit of a snow lull here in the metro area — read our previous update for thoughts on when snow will return to the rest of the region.

6:35 a.m. update: When might we see snow return to the rest of the D.C. region? Since last night, the high resolution models have been suggesting that we could see a lull in the snow around this time, so this is not unexpected. The HRRR is pegging the 7 to 9 a.m. time frame for snow to return to the metro, from south to north. That might be just a little bit fast based on what we’re seeing on radar, but it does give us a rough idea, which is helpful for people who need to get places since not everyone is off on this President’s Day.

Time is in the upper righthand corner in the forecast below.

6:10 a.m. update: Snow began to fall late last night, but since then the immediate metro has entered a lull while the far southern areas — Charles, St. Mary’s and Calvert counties — continue to see moderate to heavy snow. We’re expecting the snow to pick up across the metro and northern areas by mid-morning again, but needless to say some of our southeast areas have already reached their boom scenario where snow continues to fall.