 
|
|||||||||
              
|
Jet stream blockage equals drought, or does it?
Sunday, August 01, 1999 By Dennis B. Roddy, Post-Gazette Staff Writer
The drought of 1999 could end when Canada returns the jet stream, that cloud-pushing current of fast air that edged north of the 42nd parallel in May and has fought extradition ever since.
A storm of Old Testament proportions rumbled through the region Wednesday, downing power lines, breaking tree branches and doing just about everything but soaking in. Downpours, said climatologists, don't soak in. They run off.
"Right now, if we get an inch or two of rain in an hour, most of it runs off. What you need is a soaking rain," said Bill Drzal, a hydrologist at the National Weather Service's Pittsburgh office.
No jet stream, no long, soaking rains.
A high-pressure system hovering like a mugger over the Southern Plains states spent much of the spring and summer edging north and east, muscling the jet stream out of its normal position. The system is blamed for stretching out a long summer hot spell and exacerbating the drought.
Jeff Thatcher, a meteorologist with the weather service of Environment Canada -- that's a government bureau, not a musical review -- said jet stream or no, Toronto hasn't exactly been Water World, either, this summer.
"The grass is brown, brown, brown," he said. "Just about all of southern Ontario is dry."
Seems the jet stream might have moved north, but it didn't go native. All it did was move weird weather everywhere: drought in Pittsburgh, cold in Atlanta, snow in July in Saskatchewan, pedestrian traffic along the northern reaches of the Allegheny.
"We had to get out of the boat and actually push," said Mark Snow, whose Fourth of July canoe trip in Warren County turned into a hike down a river bed.
What's going on here?
For answers, we turned to a dozen meteorologists, a task very much like attempting to explain the economy by turning to a dozen economists. In other words, just because people can predict the weather doesn't mean they can explain it.
First there was the Bermuda High theory. It held that a high-pressure system dating to the last Ice Age, and which normally hovers just off the coast of North Carolina, had spread north, pushing aside the jet stream, blocking weather patterns and assuring Washington's title as the humidity capital of North America.
The problem with the theory, expounded in dozens of newspaper articles, is that the Bermuda High is just now high above Bermuda.
"The Bermuda High has been sitting directly over us," said Dave Malmquist, a paleoclimatologist at the Bermuda Research Station who has been trying to figure some way to get the Bermuda High to relocate to the Azores.
Bermuda is seven inches short of its average rainfall for this time of year, and the drought has left some island wells low and dry.
So what's going on? Why is the Bermuda High getting the rap when it's an unnamed cousin from near Denver wrecking the joint?
"It's a simple answer: Everybody's heard of the Bermuda High. Things are a lot more complicated than that," said Ed Olenic, a meteorologist at the National Weather Service's Climate Prediction Center in Washington, D.C.
Olenic said the no-name high front has been aided by La Nina, the massive current of cooler water in the Pacific and the evil sister of El Nino, the massive current of warm water in the Pacific.
Olenic said it had been working this way: The spring and summer sun heat up the plains around Arizona, New Mexico, Colorado and Utah. The hot air rises off the plains, shoving around the high front. La Nina sends in cold currents of air that slip in under the high front.
The high front slips into the middle of the country, bumps out the jet stream and, voila! -- Pennsylvania has a drought while cowboy country gets a monsoon.
But not everyone's buying that explanation. Dan Kottlowski, a meteorologist at Accu-Weather, based in Centre County, warns against accepting explanations with Spanish names.
"It's really difficult to look at your regional weather picture and say, 'This is the reason for this happening,' " he said.
|
||||||||
