Whenever the mercury plummets to particularly bitter temps anywhere in the United States, an oft-heard refrain is, "It's colder herethan it is in Alaska!"
But just how often is that actually the case, for, say New York City, or Chicago, or Atlanta? The answer turns out to be more days than you might think.
A climatologist - who happens to be based in Alaska - created a set of maps that shows how often cities in the lower 48 have winter days with temperatures colder than those in Anchorage or Fairbanks. Virtually all saw at least one day a winter with temps lower than those in Anchorage, which given its more southerly and coastal location than Fairbanks has a comparatively mild climate. Even parts of Florida have between 1 and 5 days a winter that are colder than Anchorage.
Days colder than those in Fairbanks, which is inland and nearer mountain ranges, were rarer, but could still be found down into the Southwest and parts of the Southeast. By the time you get up to more traditionally frigid places like the northern Great Plains, those numbers climb above 40 days a winter.
To make the maps, Brian Brettschneider, dug through historical temperature data, comparing the daily low temperatures from 756 weather stations across the U.S. to those in both Anchorage and Fairbanks for every day from December through February from the winter of 1980-1981 through 2013-2014. (He only used stations that had data for every day of winter and for a minimum of 20 winters.)
Normal lows in Anchorage are in the low teens Fahrenheit (or negative teens Celsius), compared to Fairbanks, which typically sees lows around -15°F to -20°F (-26°C to -28°C). But the variability in those winter lows is fairly high, Brettscheider said. Anchorage regularly has lows more around 25°F (-4°C) and Fairbanks can see lows around 15°F (-9°C) several times during winter.
While less of the country saw any winter days colder than Fairbanks (the extreme southern periphery of the Lower 48 had none) and fewer days when they did, Brettschneider was still surprised that the numbers were as high as they were. Boston could see anywhere from 2 to 5 days a winter with colder temperatures, while in the northern Great Plains those numbers rose above 12.
"I expected much lower numbers," he said in an email. "But, that's the value of going through this exercise. A lot of things we think are true, may not be."
The reason places in the Lower 48 see chillier weather than either Alaskan locale isn't just because of a particularly intense cold snap dipping down over the United States, but happens when there are also unusually warm temperatures in Alaska. Generally, these two circumstances are linked by the jet stream.
When it's unusually warm in Alaska, the jet stream is crimped into a pattern where it pulls warm air from closer to the tropics up to Alaska, but cold, Arctic air down toward Canada and the Lower 48 states.
"Our warmest winters (in Alaska) are usually the coldest in the Lower 48 and vice versa," Brettscheider said.
As a good example, he cites the winter of 1985: "The major cold outbreak in January 1985 produced low temperature records all through the eastern half of the Lower 48. In Alaska, it was toasty by comparison."
The last couple winters also had some examples of this - while the eastern United States was shivering in deep chills that brought the term "polar vortex" into the lexicon, Alaska was baking, sometimes even setting heat records.
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