Even though May is right around the corner, recent weather reports have been far from spring-like.
Snow fell this week on Minneapolis and Green Bay. Record-setting cold has settled on Seattle. And historic wildfires are burning in Oklahoma and Texas, where temperatures in the 90s are threatening to topple heat records. Meanwhile, 272 tornadoes swept the nation in the first half of this month – already breaking the all-time twister-count for April.
So, what's up with the weather?
According to experts, this season's higher-than-normal highs, lower-than-normal lows and extreme storms are, to some degree, symptoms of what tends to be a volatile time of year. But there are also some more insidious factors behind the latest round of weather grief, including an unusually strong La Niña, a strange pocket of warm air in Arctic, and overall climate warming.
"The weather is inherently wacky," said Paul Douglas, meteorologist and founder of Weather Nation, a weather outsourcing company in the Twin Cities, Minn. "Personally, I'm seeing an increase over time in the wackiness."
Spring is traditionally a fickle and unstable season as winter makes its slow and often ugly retreat, said Deke Arndt, chief of the Climate Monitoring Branch at NOAA's National Climatic Data Center. Violent storms are common. And it's not unusual for temperatures and precipitation levels to be higher or lower than normal. After all, that's how we end up with the artificial line called normal.
But several trends set apart the spring of 2011 from pervious years, Arndt said. For one thing, there has been an unusual stalling of weather patterns that has divided the country in two. Draw a line from Washington D.C. to Denver and down to Phoenix. North and west of that line, it has been cold and wet. To the south and east, it has been hot and dry.
"You see red blobs and blue blobs in any season, but it has been pretty entrenched for weeks to months," Arndt said. "A high-pressure ridge that has set up over the Southern Plains has been really persistent there. It has pushed a lot of active or violent weather to the east."
"It is no coincidence that there are heat and drought in Texas and Oklahoma at the same time as there's violent weather east of the Mississippi," he added. "They are not unrelated."
The current weather map fits pretty well with a typical La Niña year, in which cooler than normal waters gather beneath the surface of the eastern equatorial Pacific off the west coast of South America. The phenomenon influences the positioning of the jet stream. And that, in turn, affects weather patterns around the globe.
This year's La Niña started building late last summer and was mature by January, Arndt said. While the effect is beginning to weaken now, it remains generally strong, which helps explain why the Northwest, Northeast and Northern Plains of the United States, along with parts of Europe and Asia, had particularly harsh winters this year. It's also why many of those places are still waiting for spring to arrive.
But La Niña, which is natural and cyclical, is not the only driver behind weird weather reports lately. For the last two years, for reasons climatologists do not yet understand, a strange pocket of warm air has lingered over the Arctic, Douglas said, making the dead of winter a full 10 to 20 degrees warmer than normal in Greenland and northern Canada. The bubble has displaced cold air southward.
"If you leave the refrigerator door open, you warm up the refrigerator, and all that cool air kind of spills on to the floor," Douglas said. "That's what's happened."
On top of all that, a general rise in global temperatures has boosted levels of water vapor in the atmosphere by four percent, Douglas said. That basically loads the dice for more storms to form. Meanwhile, Twitter and Facebook can accentuate and accelerate the sense that severe weather is worse than it is.
As for what's to come, current weather patterns are poised to linger for a while longer. The atmosphere is energized, Douglas said, and jet stream winds are stronger than any other April he can remember. That means that volatility is guaranteed for the next 60 days. One meteorologist has predicted that another 300 more tornadoes will strike in the next two weeks. Whether that many pan out or not, Douglas expects this to be one of the top three tornado seasons on record.
Since we can't change the weather, the most important thing Americans do is plan for what to do when dangerous weather strikes, Douglas said. He also recommended buying a $30 NOAA weather radio, which according to the NOAA National Weather Service website, "broadcasts warnings, watches, forecasts and other hazard information 24 hours a day, 7 days a week."
An emergency radio may be one of the best forms of life insurance available, according to Douglas, who insisted that he does not make a commission for radio sales.
"Everyone needs to sit down and talk about tornado preparedness and flood preparedness," Douglas said. "It's going to be a busy spring."