Perspective

Cold, hard facts

Six things to know about the Arctic invasion

Bob Henson • January 6, 2014 | It’s hard to escape the cold weather now plowing into the eastern United States—especially if you turn on a TV or log onto Facebook. The big freeze is a compelling news story, with truly dangerous temperatures and wind chills extending into large swaths of the nation. Yet we’ve had worse: in some ways, this cold snap serves to illustrate how rare such intense events have become.

Amid all the hype, what stands out about this early winter onslaught?

Back to the 20th century—but not that far back.  Many cities in the Midwest and mid-South are experiencing temperatures unseen since the turn of the new century. As a whole, though, this cold wave won’t rival the worst of those seen up through the 1990s. This morning, January 6, Indianapolis dipped to –14°F, the city’s coldest reading since January 1994. (During that same month, temperatures reached –27°F, the city’s all-time low.) The storm has also delivered 10 to 20 inches of snow from eastern Missouri to Michigan, with several cities having some of their heaviest 24-hour snowfalls on record. The frigid Midwestern air mass should move east quickly, but there will be a number of daily records set for cold nights and cold days along its path.

300 map for 18Z on January 6, 2014
Winds ripping around a polar vortex arc from central Canada across the Midwest and back into northeast Canada, as analayzed at 300 millibars (about six miles above sea level) at 18Z (noon CST) on Monday, January 6, 2014.  Jet-stream winds topped 150 knots (172 mph) in the brighest purple band, stretching from Mississippi to Quebec. (Image courtesy NCAR/RAL Real-Time Weather Data.)

A fast mover. Part of the reason this cold front may not set many all-time record lows is because it’s moving so quickly. To get the air temperature to sink to record lows, it helps to have a calm, clear night, ideally with a deep snowpack. Just two days ago, the air mass now in the Midwest was nestled in northern Canada. A powerful dip in the jet stream pulled the frigid air south so quickly that it’s had little time to modify. (You may hear this pattern being referred to as a displacement of the polar vortex; here’s an excellent explainer from the National Weather Service.) Such setups can produce extremely low wind chills and very cold daytime readings. At noon today (January 6), Chicago was hovering near –14°F, one of the 10 coldest noontime readings ever reported there.

Many other Midwest cities are having their coldest afternoon temperatures in decades. But the conditions that foster the coldest nighttime readings may not cover as wide an area.

Ups and downs. Sometimes it’s not just the cold but the rapid swings between cold and warm that cause trouble. In between an Arctic blast during New Year’s week and the latest one, a swath of mild, humid air rocketed northward across the South and into New England, producing roller-coaster temperature swings that are quite rare in those parts of the country. The mercury dipped to 9°F in Salisbury, Maryland, on Saturday morning, January 4. By late Sunday night, it had jumped to 64°F.  By Tuesday morning, it could be back down near 10°F. Saranac Lake, New York, vaulted from –24°F late Friday night to 49°F early Monday morning. In Melbourne, Florida, readings will plummet from 79°F this afternoon to a predicted 33°F by tomorrow morning. * Update | 7 January: Salisbury reached an overnight low of 10°F, while Melbourne dipped to 38°F on its hourly measurements.

Student launching a weather balloon in heavy snow during OWLes project
The OWLeS field project is analyzing some of the nation's most intense snowfalls, which occur regularly along the south and east shores of Lake Ontario and on top of New York's nearby Tug Hill region. On the night of December 12, 2013, a University of Utah student launches a radiosonde (weather balloon) in snowfall rates of 4 inches per hour. (Photo courtesy Peter Veals, University of Utah.)

Lake effect in overdrive. When cold air sweeps over the relatively warm Great Lakes, huge snowfalls can occur along and near the downwind shoreline. This week, the contrast between the largely-unfrozen lake water and the frigid incoming air is about as strong as it gets. Between now and Wednesday, more than five feet of snow could fall on the Tug Hill region, just north of Syracuse, New York. Fortuitously, OWLeS, the Ontario Winter Lake-Effect Systems field project, is under way, with Doppler on Wheels radars and other equipment on hand to document the massive snowfall. NCAR is managing a field catalog for the project, and Jim Steenburgh (University of Utah) is blogging from the scene.

So far this winter, the warm extremes have it. The U.S. Records site, maintained by NOAA’s National Climatic Data Center, tells us that—believe it or not—the nation saw four times more daily record highs (999) than record lows (254) for the 30 days ending on Sunday, January 5.  The same period saw seven monthly highs but no monthly lows. Where has it been so warm? Largely toward the Southeast, with occasional surges up the East Coast. South Florida had one of the mildest Decembers in its history, and Baltimore experienced a low on December 22 of 62°F, its warmest on record for any day in meteorological winter (December through February).

Global temperature anomalies from NOAA for Nov. 2013
During November 2013, North America was one of the few land masses on the globe with temperatures running below the 1961–1990 average, as shown in this map of anomalies (cool colors = cooler than average, warm colors = warmer than average). It was the warmest November globally in records that extend back 134 years. (Image courtesy NOAA National Climatic Data Center.)

Climate change hasn’t stopped. Globally, we’ve just seen the warmest November in more than a century of recordkeeping. (See this post on the longer-term “pause” in global warming, which has some interesting features of its own.) This week, the cold is mostly concentrated in North America. Australia is smashing heat records, with temperatures reaching 118°F. Many Eurasian cities are well above average too: this week will see Moscow hovering in the 30s Fahrenheit, and Warsaw is expecting 40s with periods of rain.

According to Pravda, some Russians would be happy to trade places with North Americans right now: “Many people find the current winter in Russia extremely dull and depressing.”