March 16, 2018

How the South Saw More Snow Than Washington D.C. This Winter

You're not alone if you ever feel like there's a dome warding away all signs of snowy weather in your hometown. Lots of meteorologists and snow lovers take to social media every year to complain about the "snow bubble" or "snow dome" or any of the other frustrated terms we've come up with to complain about getting ripped off in the snow department. Some areas really do just miss out some winters; while snow is on the decline in some areas, the conspicuous lack of snow in one spot compared to nearby counties and states is often a fluke in the grand scheme of things.

One of my favorite weathery complaints is that it seems like thunderstorms go out of their way to miss or hit certain areas. It didn't rain here in my central North Carolina county for a long time—once that streak ended, we got slammed by a parade of severe thunderstorms almost every week, a phenomenon I half-heartedly called #Rockinghaming. I wrote about this perceived thunderstorm bubble over at Mental Floss last year; the phenomenon is so common that there's an XKCD comic strip about it.

The same can apply to snow. Two neighboring towns can see dramatically different snowfall totals from the same storm. The cutoff between feast and famine is so abrupt that it can almost seem like the satellite images and precipitation maps were faked. The fortunes of seasonal snowfall are driven by two major factors: storm tracks and storm characteristics.

Every article written about a nor'easter that doesn't include some variation of the phrase "track is everything" is doing you a disservice. The intricate dance between temperatures, moisture, and lift can be so finicky that a small deviation in a storm's track from what's expected could have a dramatic effect on who sees what.

Nobody knows that better this year than the Washington D.C. metro area. (Sorry to my friends there who find this painful to read.) One look at the seasonal snowfall map shows a glaring omission in areas that decided to participate in the snowfest we've seen south of the Mason-Dixon line this season.

I live just north of Greensboro, N.C., in the small city of Reidsville. We've gotten lucky here this year, measuring about 18 inches of snow this winter. That's well above our average of about seven inches each year. We accomplished this feat across three storms—one in December, one in January, and the storm at the beginning of this week.

Our above-average snowfall wasn't a fluke. Look across almost the entire southern United States and you'll see a trend of unusually high snowfall totals. The accumulating snow even reached the Florida panhandle. Mobile, Alabama, saw just over an inch of snow this winter. Communities south of Corpus Christi, Texas, saw more than half a foot of snow, one of the biggest storms ever recorded in that part of the country.

Washington's National Airport has only recorded 3.7 inches of snow this winter. Dulles Airport off to the west has only seen 6.6 inches of snow, which is around a third of what they see in an average season. Compare that to Baton Rouge, Louisiana—you know, that ol' icebox—where they've seen a cool four inches of snow this season. Jackson, Mississippi has seen nearly six inches of snow, Atlanta nearly five, Virginia's capital city just over ten, and even more than double D.C.'s total down in Raleigh, N.C.

The most noticeable hole in the seasonal snow map above is in the middle of the United States. The lack of snow in the center of the country is a result of the dominant weather patterns across North America this winter. Dallas has only seen a trace of snow so far. Oklahoma City's paltry dusting is far below their seasonal average of seven inches. St. Louis and Kansas City have seen less than half of what they should in a normal winter. Temperatures have been near average for the past couple of months in these areas. However, high pressure has dominated the center of the country for most of the season, deflecting any real chances at winter storms and keeping those that did come through mostly rain or ice.

But why has the atmosphere been such an anti-dendrite in the Mid-Atlantic this year? It's the storm tracks. The storms that rolled toward the East Coast never took the right track to hit D.C. The storm tracks this year have missed the D.C. area to the south, giving towns from Texas to Florida and beyond rare snow days, to the east as nor'easters skirted a little too far off the coast, and to the north in Pennsylvania. The pattern of snowfall totals this year almost resembles a snow shadow with the Appalachian Mountains wringing out all the moisture before any energy can deliver it farther east.

D.C.'s snowy misfortune isn't the whole story. New England has seen its fair share of wintry precipitation this year. But the most recent nor'easter—the third one this month—left a noteworthy lack of snow in a certain spot. Take a look at the pattern of snowfall totals after the nor'easter on March 13:

See that stripe of lower snowfall totals through central Massachusetts? That's not a data error. While the area in question lies in the Connecticut River valley, lower than its surroundings to the east and west, the snow bands really did set up in such a way that towns like Amherst barely had enough to shovel while towns just to the east and west got clocked with more than a foot of snow.

You can see the snow bands clearly in radar images from the event:

The intense bands of snow on the northwest side of a nor'easter form in what's known as the deformation zone. The deformation zone is part of the storm where upper-level winds collide; this zone is the classic "comma head" that makes these storms so beautiful on satellite imagery. These winds fan out laterally and create enhanced lift in the atmosphere. This lift leads to the intense bands of snow that can bury towns in feet of snow.

Sometimes you see one dominant band of snow and sometimes it comes together as multiple strong bands. The storm on March 13 was one of the latter scenarios. The end result was a remarkable hole in snowfall totals in central Massachusetts that only measured a dozen or so miles wide, all while towns on either side get smacked by the intense bands.

There are a few more chances of snow before the warmth finally wins out against the stubborn winter air. It's far too early to tell, but the pattern looks favorable for another East Coast storm, and hey, D.C. could finally get its respectable snow after all. Stranger things have happened.

[Maps: Dennis Mersereau]

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I graduated from the University of South Alabama in 2014 with a degree in political science and a minor in meteorology. I contribute to The Weather Network as a digital writer, and I've written for Forbes, the Washington Post's Capital Weather Gang, Popular Science, Mental Floss, and Gawker's The Vane. My latest book, The Skies Above, is now available. My first book, The Extreme Weather Survival Manual, arrived in October 2015.