Arctic warming blamed for last year's heat and this year's chill - Omaha.com
Published Saturday, March 30, 2013 at 1:43 am / Updated at 1:58 pm
Arctic warming blamed for last year's heat and this year's chill

Daffodils and crab apples were putting on their show.

Golf courses and ballfields were packed.

Planting was under way in backyard gardens.

Such was the record warmth of March 2012.

Fast forward a year: The soil's been too cold for planting, trees and flowers have yet to bud, and cabin fever has taken hold.

“A tale of extremes,” said Barbara Mayes, a National Weather Service meteorologist.
Extremes that are flip sides of the same coin.

Mayes said atmospheric blocking in the upper part of the Northern Hemisphere contributed significantly to the contrast in the two months. This year, the blocking has stalled over Greenland and Iceland. Last year it was above northern Europe.

Similar blocks also fueled eastern Nebraska's near-record heat in July 2012 and record snows of December 2009, she said.

Research into blocking patterns has intensified because of their impact on daily life, said Bob Henson, a meteorologist and spokesman for the University Corporation for Atmospheric Research in Boulder, Colo. By the time the blocks ease, they can leave behind a “stack of broken records,” he said.

This March has not approached record status. Late in the week, it was on pace to be Omaha's 32nd-coldest in 142 years, Mayes said.

But it has been substantially colder than a year ago — daytime highs in Omaha have averaged about 27 degrees below those of March 2012. Last March was by far the warmest March on record in the United States.

Wild swings in weather are characteristic of life in Nebraska and Iowa, particularly during transition seasons like spring.

But research indicates something beyond the regular wildness is at play. Increasingly extreme weather has long been believed to be a hallmark of climate change, but a direct connection to current extreme weather has proved elusive. In recent years, that has begun to change.

Emerging research has found an explanation of how additional warming in the Arctic may increasingly influence these blocking patterns.

The research began with a simple question posed by Jennifer Francis, a Rutgers University atmospheric scientist, and Stephen Vavrus, a University of Wisconsin-Madison atmospheric scientist: Is the accelerating warmth in the Arctic affecting weather across the mid­latitudes (which includes the lower 48 U.S. states)?

Their analysis found a correlation, she said, one that also sheds light on the hard-to-forecast blocking patterns. Their research has been peer-reviewed, an essential benchmark for serious science, and was published in Geophysical Research Letters.

To understand the research, it's important to know the role that a river of air in the upper atmosphere known as the jet stream plays in the weather.

Storms tend to hitch a ride along the jet stream, so it influences who gets rain or snow and who remains dry. It also demarcates the line between Arctic air and warm air to the south.

The jet stream gets much of its strength from the temperature contrast between Arctic air and warmer air farther south.

Here's how Francis explained the relevance of her Arctic research to weather in the middle of the United States:

The Arctic is warming at two to three times the rate of the rest of the globe. As it warms, there's less contrast between the temperature of Arctic air and the atmosphere farther south. As a result, the jet stream weakens.

A strong jet stream tends to flow fairly directly, west to east. A weakened jet meanders at a slower pace, looping north and south.

The consequences:

» A weakened jet is more likely to form atmospheric blocks, which tend to create “stuck” weather patterns.

» The meandering allows Arctic air to plunge southward or warm air to surge northward.

» Combined, these two factors stack the odds in favor of prolonged hot or cold spells and contribute to stalled storm systems.

Last March, much of the United States, including Nebraska and Iowa, was locked under a northward loop that allowed warm air to rush up from the south.

This year, much of the Upper Midwest, including eastern Nebraska and Iowa, and the Northeast U.S. have been stuck under a southward loop that allowed Arctic air to move south.

Francis said weather is complex, so this research doesn't explain all that is happening. But the findings are of increasing importance because the Arctic is warming so rapidly, she said.

Research indicates that these patterns are extending beyond fall and winter and are reaching into early spring. Further encroachment into warmer months is possible.

“We're heading into brand new territory,” she said.

Contact the writer: 402-444-1102, nancy.gaarder@owh.com


Current conditions and forecast

Contact the writer: Nancy Gaarder

nancy.gaarder@owh.com    |   402-444-1102    |  

Nancy writes about weather, including a blog, Nancy's Almanac. She enjoys explaining the science behind weather and making weather stories relevant in daily life.

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