Well, it's back — sort of.
Forecasters say polar air from the Arctic Ocean is expected to arrive in Canada and the United States next week, bringing unseasonably cool temperatures to the eastern half of the country. Temperatures in Chicago will top out in the low 70s by midweek, making it seem like mid-September rather than mid-July. Compare Wednesday's forecasted high — 72 degrees — with the temperature on July 16, 2013: 93 degrees.
Similarly comfortable temperatures are expected as far south as Texas, part of what the National Oceanic and Atmospheric Association calls a "backward trajectory" of air.
According to the National Weather Service, temperatures could fall to about 20 degrees below normal in Kansas and Oklahoma.
The pattern "has been a recipe for extreme warmth on the West Coast and colder than average weather out East," Eric Holthaus, Slate's resident meteorologist, notes. "On the west side of the Rockies, tropical Pacific air gets funneled northward from around Hawaii toward Alaska while California dries out and roasts; on the other side, cold air from the Yukon cascades southward toward the Midwest and East Coast."
But not everyone is thrilled with the summer "cold" snap.
"This Polar Vortex couldn’t arrive at a worse time," Jerry Shields writes on Local2.com in Sault Ste. Marie, Ontario. "Instead of warm summer-like conditions it will feel more like fall. Temperatures are likely to be 5-10°C below normal. This will keep daytime highs buried in the teens with overnight lows in the single digits."
But not every meteorologist agrees the unseasonable plunge is a polar vortex.
"That's a wintertime phenomenon," Dan Petersen, a meteorologist with the National Weather Service, told Reuters. "The basic idea (is) of a large area of below-normal temperatures and some very impressive anomalies for the central and southern Plains."