This is the heart of meteorological winter, experts claim. The coldest period in the Washington area is from Jan. 12 to Jan. 23, according to the National Climatic Data Center’s 30-year “climate normals.”
But abnormality is apparently this year’s normal: The National Weather Service’s outlook shows more of the same snowless weather through the rest of January.
A cold front is blowing into town, and a few snowflakes may make a cameo appearance here and there. At some point there may even be a sighting of the famous “wintry mix.” But by Sunday the mild weather is expected to return.
The snowless winter of 2012 is a national phenomenon. Outside of Alaska (brutally cold and buried in snow), the Pacific Northwest and the Arizona mountains, America is strikingly snow-starved.
In the mid-Atlantic, winter has become a boom-or-bust phenomenon. For two straight years, the Interstate 95 corridor was
clobbered by historic snowfalls. The Richmond-to-Philadelphia stretch got it two years ago — including Washington’s Snowmaggedon of Feb. 5, 2010 (32.4 inches of snow at Dulles International Airport) — and then the Philadelphia-to-Boston stretch took the brunt of it last year.
This year, there’s enough moisture around, generally, to produce snow in the East, just not enough cold. This appears to be part of a long-term trend. Snow has become gradually scarcer in the Washington region in recent decades, according to an analysis by Jason Samenow of The Post’s Capital Weather Gang. Average annual snowfall at the region’s three major airports has been declining by roughly an inch per decade, Samenow found.
Blame for this year’s snow deficit can be assigned in layers, from the meteorological to the climatological, from the simple to the complex and on to the speculative.
As always, one must start with the jet stream. The jet stream has gone zonal on us.
“The jet stream has been persistently to our north and in what we call a zonal flow pattern, where it goes pretty much straight west to east instead of having those dips and ridges, those troughs and crests,” said David Robinson, the state climatologist of New Jersey and a professor of geography at Rutgers who specializes in the study of snow cover in North America.
This straight-line jet stream keeps cold air in the frozen north rather than dragging it into the temperate south. Fairbanks, Alaska, had an average January temperature of 25.9 degrees below zero through Jan. 16, which is 18 degrees below the 30-year average. Valdez, Alaska, had recorded 26.5 feet — feet — of snow by Jan. 12.
The jet stream has confounded airlines that ply the North Atlantic airways, with some of the smaller jetliners from Europe forced by headwinds to refuel in Newfoundland on their way to the United States.
The jet stream is, in turn, affected by the North Atlantic Oscillation, which — and yes, there will be a test — is in its “positive phase.” What this means, basically, is that there’s relatively low pressure over Greenland. If, instead, there were high pressure over Greenland — a “blocking high” — the air mass would act like a blast shield, forcing the jet stream to dip south into temperate latitudes in North America. Blocking highs are common — just not this year.
One deeper layer of causality may be climate change, which scientists attribute in part to the burning of fossil fuels, and which has been particularly dramatic in the Arctic. There has been, for example, a steady year-to-year decline in the percentage of the Arctic Ocean permanently covered in ice.
It could be, Robinson said, that the changes in the Arctic are contributing to what appears to be a more flip-flopping weather pattern. The number of big-snowfall years seems to be about the same as ever, he said, but there are more years with little or no snowfall.
“Snow by its very nature, it’s boom or bust, particularly here in the middle latitudes,” Robinson said. “The climate system is exhibiting more extremes. We see this in annual rainfall. We see this in some annual snowfalls.”
There have been many mild winters before, noted Steve Zubrick, a meteorologist with the National Weather Service. Zubrick has run the numbers on Washington winters going back to 1872. He looked at the first half of meteorological winter, from Dec. 1 to Jan. 15. This year’s average temperature, 43.5 degrees, was the seventh-mildest on record — warm, but not as warm as (starting with the warmest ever) 1889, 2006, 1931, 1949, 1982 or 1971.
As for the lack of snow, that’s not so strange, Zubrick said. There are 16 half-winters on record with no measurable snow in Washington.
There are tentative signs, Robinson said, that the North Atlantic Oscillation’s positive phase could be tipping back toward the negative, which means Greenland would go into jet-stream-
diverting mode again and the February weather in North America would be more traditionally wintry.
If there’s a blizzard yet to come this winter, the experts have a scale with which to assess the severity of it. It’s called the Northeast Snowfall Impact Scale. There are five categories: Extreme, Crippling, Major, Significant, and Notable.
So far this winter, Reagan National Airport has recorded 0.6 inches of snow.
There’s no word for that.