Death Valley will be unbearable this weekend. Forecasters predict temperatures of up to 129 degrees, approaching the world record of 134, set in 1913.
A week ago, historic heat struck several Alaskan towns, with highs in the 90s. About the same time, the Canadian city of Calgary experienced another extreme — torrential rains and flooding that inundated the city.
Dramatic fluctuations in weather have occurred repeatedly in recent years, including unrelenting snow in New England and monster tornadoes in Oklahoma.
The culprit? Some scientists and forecasters are pointing to abnormal shifts in the jet stream.
"When your large-scale jet stream patterns are funky, that's when you get extreme weather," said Jeff Masters, director of meteorology for Weather Underground.
The polar jet stream blows from west to east across the United States and is a key determinant of weather in much of the country.
Normally, cold air from the north and hot air from the south collide near the middle of the nation, accelerating the jet stream in a slightly wavy pattern.
As the Arctic has warmed in recent years, some scientists say, the temperature differential between cool and hot air has decreased, slowing parts of the jet stream and allowing it to meander more like a roller coaster.
"The north-south waves, or undulations, that the jet stream takes as it travels around the Northern Hemisphere are slowing down," said Jennifer Francis, an atmospheric scientist at Rutgers University who co-wrote a paper on the subject last year.
These waves lift warm air north and drive cold air south. It was a particularly high wave that carried 90-degree weather into Alaska. Another wave is blanketing the West with oppressive heat this weekend.
Waves, or undulations, have always been a part of the jet stream.
But they have been more pronounced in recent years, Masters said. Some scientists, such as Francis, think that such variations are tied to climate change. Others are not certain.
Bay News 9 meteorologist Josh Linker said the jet stream is a factor in odd weather, but he is less convinced that anything extraordinary is happening with its movement. "I don't think that dips and peaks and valleys in the jet stream are anything unusual," he said.
He said the polar jet stream generally travels well north of Florida at this time of year and should not have much effect on Tampa Bay this summer.
Still, Masters said, it was an unusually sharp dip in the jet stream in 2004 that pushed Hurricane Charley toward the west coast of Florida.
If the Arctic continues to warm, more significant weather could be on the way, he said.
"We should expect that as the Arctic continues to heat up more and more relative to the rest of the globe, we'll see an increase in extreme jet stream behavior," Masters said.
Information from the Associated Press was used in this report. Zachary T. Sampson can be reached at firstname.lastname@example.org or (727) 893-8804. Follow him on Twitter @zacksampson.