Widespread 15-25 inch snow amounts are rare in the mid-Atlantic any time of winter. For perspective, a storm the caliber of Snowpocalypse easily equals or surpasses an entire average D.C. winter season in a matter of 24 to 30 hours.

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What became the biggest snowstorm since 2003 not only made it into Washington’s top 10 snowstorm list while setting a new December standard, it also followed a story line that would be closely repeated later in the historic winter of 2009-10.

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The winter it just had to snow

The overall signs of winter 2009-10 were quick to show themselves — it was going to snow at almost every real opportunity and area residents were going to be at the mercy of nature for extended periods.

While the December 5 storm two weeks prior could have been overlooked as pure coincidence, the major East Coast snowstorm to follow was — without question — the “real deal” of a loaded-gun El Nino winter.

A persistently strong “high-latitude blocking” pattern – specifically high pressure over Greenland that helps funnel cold into the area – helped set the stage for the storm.

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09-10 Five Years Later (series): ‘Unusually early’ snowfall sets the stage

Other ingredients, including an interaction between El Nino’s moisture-laden tropical jet stream and an energetic low-pressure system hustling along through the northern United States, popped the proverbial cork. The recipe created an explosive mixture that combined to spawn a strong coastal low pressure system which produced results not often seen in the Washington region, and never so early in the season.

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Watching it come together

Signs that weather pattern may foster a major storm appeared on some computer models days to even weeks in advance. It was evident that it was great pattern for a storm

But great patterns don’t always produce great storms. With a favorable pattern in place, we start tracking possible storms in the bevvy of computer simulations which may spray low pressure systems from the Great Lakes to Bermuda. As time passes, the goal posts close. Sometimes the ultimate storm track is “just right” for snow, but often it is not.

Many remember that the big storms of 2009-10 were well forecast. That’s true to a degree. The big Greenland Block that was present helped make things a bit more predictable than they might otherwise be. But Snowpocalypse, while the players were on the field further in advance, was a little tricky to make a call on until a few days out.

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Even here at CWG we were only forecasting a chance of snow showers (while hedging on the risk of something more significant) four days out from the storm.

But finally goal posts had closed, and it was apparent the storm track was perfect for a blockbuster event. We issued our first alert that big accumulations might become a risk roughly 48 hours before the first flakes began flying.

It almost seemed we’d gone snow crazy. Then it happened.

The storm begins

Snowpocalypse started getting its act together on Thursday, December 17, 2009 as a large mass of moisture associated with a low pressure system forming in the Gulf of Mexico. Taking a classic track for an eventual monster East Coast snowstorm, it moved through the Gulf of Mexico into north Florida.

The storm then swung to the North Carolina coast before heading northeast to a position off of eastern New England prior to departing out to sea. During this time its central pressure deepened through the 980s (mb) while it was east of the Mid-Atlantic. Pressures of that level are roughly equivalent to those of a strong category 1 hurricane.

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While the Washington area anticipated the arrival of the storm on Friday the 18th, a state of emergency was declared in Virginia and a snow emergency was announced starting Saturday morning in Washington. States of emergency were eventually expanded to most of the region.

Snow moved in and started to accumulate across the area in the hours surrounding midnight on December 18 and 19. At the same time, it accumulated quickly to the south and west of the area. Blizzard warnings were hoisted for Prince George’s, Anne Arundel and Calvert counties in Maryland. Much of the overnight snow was light-to-moderate but trending heavier. Several inches of fairly powdery snow were on the ground in the metro area by sunrise.

As Saturday morning wore on, the rapidly developing system off the North Carolina and Virginia coast began ejecting bands of blinding snow to the north across the region.

National Airport reported heavy snow — with visibilities as low as one-eighth of a mile — from 10 a.m. until 3:30 p.m. on Saturday the 19th. 6 inches fell there during that period, while other locations in the area saw even higher rates (as much as 2-3 inches per hour) accumulations.

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Blizzard warnings were extended westward to the District on Saturday, but they did not end up verifying locally. It was windy either way. Sustained as high as 20 to 25 mph in the city, but officially you look for sustained winds of 35 mph for three hours concurrent with a visibility of one-quarter mile or less for a real blizzard.

The storm was either a true blizzard or close at a handful of coastal locations. Moderate drifting of snow was observed throughout the region, especially in more rural locations after the storm’s passage.

Light to occasionally moderate or heavy snow continued into Saturday evening as upper-level energy associated with the departing coastal low passed through the region from the west. Snow finally concluded overnight, over 24 hours after it began.

The perfect snowstorm?

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Incredibly, for the D.C. area at least, most spots (except well south and east) did not change to sleet or rain during the entire event.

As far as big storms go in the region, this is a rarity. The area’s proximity to the Atlantic Ocean and its relatively southern latitude often promotes some warm-air intrusion which cuts down on totals. An example of that is the famed Presidents’ Day storm of 2003 (6th biggest on record for D.C.). Snow turned to sleet in the immediate D.C. area and kept accumulations from reaching truly astounding levels during that event.

Cold air was effectively funneled into the area thanks to the pattern setup that included a surface high pressure in Canada and other features including the Greenland Block as well as an upper-level low pressure northeast of New England. This combination pushed air downward from the North Pole region and into the area. Temperatures remained in the mid-and-upper 20s for the entire accumulation portion of the event after only rising slightly above freezing on the 18th before snow began.

Additionally, big Washington area storms often produce dry slots, a portion of the storm lacking precipitation near the low center. In those regions, snow, sleet or rain will shut off during the height of an event. It can prove devastating for a snow lover.

During the Blizzard of 1996 (number 5 all time in D.C.), a dry slot caused the snow to end for many hours. During Snowpocalypse, the dry slot stayed just east of the area, mainly impacting the Chesapeake Bay area and eastward toward Delaware. This one just kept going and going until it was over.

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The radar loop is pure joy for snow fanatics. Watch it again.

Snowpocalypse ultimately dumped 16.4 inches of snow at National Airport making it — at the time — number 7 on the list of D.C. snowstorms. The first blizzard of February 2010 would later knock it back to number 8. The storm is also the largest ever in December, and it helped set a new D.C. December snowfall record of 16.6 inches. The one-day snow total for December 19 ranks third on record for one calendar day in D.C.

In other parts of the city, and the wider area, reports ranging from 18 to 26 inches were fairly numerous, including 20.5 inches in Arlington, Va., 24 inches in Bethesda, Md. and 26.4 inches in Damascus, Md. At Baltimore-Washington International, a total of 18 inches fell with 17 inches coming in one calendar day. That pummeled the old one-day December record of 11.5 inches. Dulles International picked up 18 inches with 16 coming in one day, setting a new single-day December record.

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Lengthy impacts

Even though the storm occurred over a weekend, its effects lingered into the beginning of the following week for most folks across the region. Longer for some. Like the majority of Washington’s largest snowstorms, the immediate aftermath of the storm saw the area struggle to regain a foothold after being truly crippled.

Significant segments of transportation remained at a standstill into Sunday the 20th. Area business, cultural and entertainment centers, as well as government and schools all struggled to get back to normal. Yet with stores eager to do business, last-minute Christmas shoppers with access to a vehicle that could withstand snowy road conditions were able to find many retailers open.

Hundreds of flights into area airports were cancelled during the storm and after, with at least temporary halts in all traffic reported. At National and Dulles, several runways were not cleared until Sunday, a full day after the last snowflakes fell.

All above-ground Metro stations, which closed as the storm cross-checked the region on Saturday, remained shut through at least Sunday night. Metro bus lines were also suspended during the height of the storm and into Sunday morning, with some routes closed even longer. Bus service was also stopped for the night on Sunday evening following the storm due to icy road conditions.

Even football was impacted by the snow. We just saw that in Buffalo, NY following their own Snowpocalypse. It’s big deal any time it happens.

In Baltimore, officials were forced to push the Ravens’ Sunday start time back to 4:15 p.m. from 1 p.m. to give crews enough of a chance to clear the stadium. Workers brought in by the Washington Redskins were graced with a Monday night game, but they had the task of removing an amazing 25 million pounds of snow from inside the stadium (plus all the stuff in the parking lots).

After Monday’s government-induced snow day, life more-or-less returned to normal in the city by Tuesday. Traffic and the commutes were, as usual following a big storm, nightmarish.

Since some area schools were already closed for the holidays, and others were planning on doing so by mid-week, a vast majority of students had a few extra days to play in the snow and enjoy not going to class.

Compared to some snowstorms in the area like the first Presidents’ Day storm in 1979 (number 3 all time), snow remained on the ground for a lengthy period afterwards. Much of the region held about one foot of snow cover through Tuesday the 22nd as daytime temperatures following the event were mainly in the mid-and-upper 30s and nighttime lows fell below freezing.

A sorta-White Christmas, and this is only the beginning?

Those hoping for the not-so-common white Christmas in D.C. were rewarded — at least when they woke up on the 25th. Only 13 years on record have had 1 inch or more of snow on the ground in D.C. on Christmas. The 7 inches on the ground at D.C. Christmas morning 2009 tied that of 1966 for the most on record.

The roughly one foot of snow that remained on the ground across the area on Christmas morning was mostly wiped out by a storm (mainly rain with some wintry mix) that occurred late in the day and into the next.

Temperatures rising into the 50s ensured that by the 26th most locations were back to largely bare ground. Only snow piles, a few drifts, and lots of memories were the remains of the Blizzard of 2009.