Tornado Season Intensifies, Without Clear Scientific Consensus on Why

KANSAS CITY, Mo. — All the warning sirens echoing across the Great Plains, Midwest and Southeast this month leave little doubt that the tornado season — which has plowed a trail of destruction through communities from Oklahoma to Wisconsin to Georgia — is off to an unusually busy start.

So far this year, tornadoes have killed 41 people and torn apart countless neighborhoods and, this weekend, one major airport.

Now, as the country braces for several more days of potentially violent weather, meteorologists say the number of April tornadoes is on track to top the current record. There have been, according to preliminary estimates, about 250 tornadoes so far this month and, in all likelihood, more are still to come, said Greg Carbin, the warning coordination meteorologist for the National Weather Service.

“It’s unusual but it does happen,” said Howard Bluestein, a meteorology professor at the University of Oklahoma who specializes in tornado research. “This isn’t a sign that the world is about to end.”

Those same experts note that drawing conclusions about the true size of, or reason for, an increase in tornado activity is difficult because historical statistics are unreliable due to changes in the way storms are tracked and measured.

Although the average number of April tornadoes steadily increased from 74 a year in the 1950s to 163 a year in the 2000s, nearly all of the increase is of the least powerful tornadoes that may touch down briefly without causing much damage. That suggests better reporting is largely responsible for the increase.

There are, on average, 1,300 tornadoes each year in the United States, which have caused an average of 65 deaths annually in recent years.

The number of tornadoes rated from EF1 to EF5 on the enhanced Fujita scale, used to measure tornado strength, has stayed relatively constant for the past half century at about 500 annually. But in that time the number of confirmed EF0 tornadoes has steadily increased to more than 800 a year from less than 100 a year, said Harold Brooks, a research meteorologist at the National Severe Storms Laboratory.

In April 1974, for example, there was a record 267 tornadoes reported, but the actual number that occurred is believed to be closer to 500.

“Today we seem to know about every single tree branch knocked down,” Mr. Carbin said. “We have eyes everywhere, and we have radar and satellite. It would be very difficult for a tornado to sneak through unnoticed.”

Tornadoes form when warm moist air combines with powerful dynamic winds inside a thunderstorm, sending a funnel cloud spinning toward the ground. They are most common in spring, typically peaking in May.

Though scientists believe that climate change will contribute to increasingly severe weather phenomena, including hurricanes and thunderstorms, there is little consensus about how it may affect tornadoes.

It remains unclear, partly because of the lack of historical data and partly because of their unpredictable nature, whether they will increase in number or strength or geographic range.

The large number of tornadoes so far may simply reflect normal variability, said Mr. Brooks.

Those assurances do not mean much to people like Kandice Shaw, a frequent business traveler who arrived at her hometown airport in St. Louis to find most of the windows boarded up and many other signs of storm damage. She worried about the increase in violent weather this spring. “We’ve had nothing but tornadoes,” she said. “I feel like I’m living in the Land of Oz.”

 

Tornado Season Intensifies, Without Clear Scientific Consensus on Why

 

KANSAS CITY, Mo. — All the warning sirens echoing across the Great Plains, Midwest and Southeast this month leave little doubt that the tornado season — which has plowed a trail of destruction through communities from Oklahoma to Wisconsin to Georgia — is off to an unusually busy start.

So far this year, tornadoes have killed 41 people and torn apart countless neighborhoods and, this weekend, one major airport.

Now, as the country braces for several more days of potentially violent weather, meteorologists say the number of April tornadoes is on track to top the current record. There have been, according to preliminary estimates, about 250 tornadoes so far this month and, in all likelihood, more are still to come, said Greg Carbin, the warning coordination meteorologist for the National Weather Service.

“It’s unusual but it does happen,” said Howard Bluestein, a meteorology professor at the University of Oklahoma who specializes in tornado research. “This isn’t a sign that the world is about to end.”

Those same experts note that drawing conclusions about the true size of, or reason for, an increase in tornado activity is difficult because historical statistics are unreliable due to changes in the way storms are tracked and measured.

Although the average number of April tornadoes steadily increased from 74 a year in the 1950s to 163 a year in the 2000s, nearly all of the increase is of the least powerful tornadoes that may touch down briefly without causing much damage. That suggests better reporting is largely responsible for the increase.

There are, on average, 1,300 tornadoes each year in the United States, which have caused an average of 65 deaths annually in recent years.

The number of tornadoes rated from EF1 to EF5 on the enhanced Fujita scale, used to measure tornado strength, has stayed relatively constant for the past half century at about 500 annually. But in that time the number of confirmed EF0 tornadoes has steadily increased to more than 800 a year from less than 100 a year, said Harold Brooks, a research meteorologist at the National Severe Storms Laboratory.

In April 1974, for example, there was a record 267 tornadoes reported, but the actual number that occurred is believed to be closer to 500.

“Today we seem to know about every single tree branch knocked down,” Mr. Carbin said. “We have eyes everywhere, and we have radar and satellite. It would be very difficult for a tornado to sneak through unnoticed.”

Tornadoes form when warm moist air combines with powerful dynamic winds inside a thunderstorm, sending a funnel cloud spinning toward the ground. They are most common in spring, typically peaking in May.

Though scientists believe that climate change will contribute to increasingly severe weather phenomena, including hurricanes and thunderstorms, there is little consensus about how it may affect tornadoes.

It remains unclear, partly because of the lack of historical data and partly because of their unpredictable nature, whether they will increase in number or strength or geographic range.

The large number of tornadoes so far may simply reflect normal variability, said Mr. Brooks.

Those assurances do not mean much to people like Kandice Shaw, a frequent business traveler who arrived at her hometown airport in St. Louis to find most of the windows boarded up and many other signs of storm damage. She worried about the increase in violent weather this spring. “We’ve had nothing but tornadoes,” she said. “I feel like I’m living in the Land of Oz.”

 

Poor Season for Sunshine Is Great One for Spores

Psychology: “You just have to carry on,” said Molly Corrigan, soaked citizen of this so often sunless city.

Utility: “Abundant Snowpack Assures Healthy Electricity Supplies,” trumpeted Seattle City Light, which generates most of its power through hydroelectric dams.

Danger: “Washington family survives avalanche in vehicle,” read a recent headline.

Little League: “Field closed,” say the sad signs on the diamonds.

And then there is the evidence procreating beneath your feet, through your yard, up on your roof, down your gutters and into your dreams: the march of the moss.

“The spores were really active this year,” said Robert Braid, caretaker of the Bloedel Reserve on Bainbridge Island, across Puget Sound from Seattle.

Inara McEwen, sitting on a bench by a reflecting pool at the reserve, noted the diversity: “There’s the moss that grows on trees, and there’s the moss that grows in your car.”

When Mr. Braid speaks about spores being active, what he is really saying is that after a particularly rainy winter (thank you, La Ni?a) and now amid a particularly rainy early spring (thanks again), the atmosphere has been ideal for moss to multiply. And so it has been doing just that.

That means this wet region is once again confronting its moss divide.

“So many of the calls we get are from people who actually want to get rid of moss,” said Sue Hartman, who helps answer the gardening hot line run by Seattle Tilth, which promotes organic and sustainable gardening. “But this being the Pacific Northwest, moss is really kind of a native plant. I personally love moss, and my pals here at Tilth also love moss.”

Noting that this has been “an extraordinary year for moss,” Ms. Hartman said Seattle Tilth tried to provide “a little therapy” for people whose image of a lawn or garden bed does not necessarily include moss.

“When we see something that doesn’t look right to us, our first instinct is we need to correct it,” Ms. Hartman said. “But if moss is growing somewhere, it’s growing there for a reason. Perhaps you’re trying to grow grass in a place where grass doesn’t want to grow.”

Of course, moss and grass are not always at odds. Sometimes moss grows on roofs, then grass grows in the moss and an ecosystem is born.

“We’ve just gotten more and more into moss because it’s been so much wetter,” said Mitch Jacobsen, co-owner of Better Window Cleaning Seattle. “There’s money in moss.”

Mr. Jacobsen and an employee, Tai Koenig, were about to scale the roof of Ms. Corrigan’s two-story home on another drizzly morning in Seattle’s Ballard neighborhood. For about $400, the men would rake and clear the roof, clean the gutters and then treat the roof with chemicals to slow the inevitable regeneration of moss.

Ms. Corrigan said that she and her husband were having the roof cleaned mostly for maintenance, but that they also hoped removing its soft mossy habitat would discourage a pair of raccoons known for their own procreative endeavors — “rooftop romance,” she called it. Neighbors had taken notice. Photographs were well-circulated.

“I don’t think they will like the rough asphalt,” Ms. Corrigan said of the roof tiles.

This push and pull between people and the elements here is constant but not always predictable. Mr. Jacobsen said his company often wrestled with what chemicals to use on roofs. While some residents have no problem with powerful phosphates, others who want moss removed worry about the runoff — particularly the increasing number of people who capture roof runoff in cisterns to water their vegetable beds. Then again, some of the newest “green” houses have roofs with moss deliberately planted on them.

At Bloedel Reserve, which claims to have the largest moss garden on the continent, growing moss — and keeping it from growing — takes work. Mr. Braid said he had noticed in recent years that the winter frost window had narrowed, and that the moss on rocks in the Japanese garden area had expanded in response. The problem is that the rocks are not supposed to be completely covered.

“You have to find that balance of just the right amount moss on there,” he said.

Mr. Braid, who has been at the reserve for 26 years, has cared for the Japanese garden for 15. Last year the moss garden was added to his duties. He spends his days weeding wetlands, pulling overgrown huckleberry bushes, planting an alder or hemlock tree, always seeking a balance of light and moisture, for the moss.

“It’s peaking right now,” Mr. Braid said.

Seattle has a longtime opinion columnist, Knute Berger, whose nickname is Mossback. He often writes about preserving the built environment, of finding a balance between making way for the future and respecting decay.

Asked about moss, Mr. Berger said, “I’m all for letting it grow.”

Mr. Berger, who does most of his work here for Crosscut, an online journal, pointed out how wealthy the city had become over the past few decades, how new people with new money sometimes tore down little old houses — sometimes houses that are covered with moss — and built big new ones in their places.

“There’s something about the moss image to me that is kind of the democratizing aspect of nature,” Mr. Berger said. “You might have a lot of money and you can fend most of it off, but you’re still going to have some moss on your roof.”