'El Nino' blamed for frigid weather

January 19, 1994|By Frank D. Roylance | Frank D. Roylance,Staff Writer

Somebody called The Sun this week and blamed this month's frigid weather on "that Hubble repair flight in December. It disrupted the jet stream and made us all freeze down here," the caller complained.

He may have been half right.

Meteorologist Russell L. Martin of the National Weather Service's Climate Analysis Center in Camp Springs says something has indeed disrupted the jet stream, which steers weather systems across North America.

But Mr. Martin points at "El Nino," the periodic warming and cooling of Pacific Ocean waters, which can send the jet stream unusually deep into the Arctic and bring it roaring back down across the central and eastern United States with deadly cold, snow and ice.

Happily, the latest blast of arctic air -- which has sent temperatures to the single digits as far south as Mississippi -- should be the last for a while, he said.

"We should be getting into a warmer phase, though we may still see some above-normal precipitation," Mr. Martin said of the current 30-day forecast. But then, "these things can always be wrong."

Fred Davis, chief meteorologist for the weather service at Baltimore-Washington International Airport, said that forecast calls for above-normal temperatures and precipitation through mid-February. Highs in the 40s are due by next week.

This winter has been unusually cold in Maryland.

Since the first day of winter, Dec. 21, Mr. Davis said, "we've only had six days of above-normal temperatures, three days about normal, and 18 days below normal. That's why we're feeling it. It's been a tough winter for the first 27 days."

January has averaged 28.1 degrees, or 3.7 degrees below normal through the 17th, he said.

Even so, January hasn't approached the coldest one on record at BWI. In 1977, the Bay froze over and temperatures averaged 22.9 degrees -- nearly nine degrees below normal.

As for snow, that depends on where you live. At BWI, where much of the precipitation has been mixed, instruments have recorded 4.7 inches of snow all season, far from the seasonal average of 20.5 inches. Even Ocean City has had more -- 9 inches.

And Oakland, in Garrett County, has already recorded nearly 80 inches of snow -- 2 inches above normal for a whole season. (The record is 126 inches in 1959-60.)

"People are a little tired of snow, I'm sure, but we just keep going," said Bea Crosco, part-owner of Flowers by Weber in Oakland. At 4 p.m. yesterday, it was minus 8 degrees with 40 inches of snow outside.

The big weather news lately has been the deep cold and below-zero wind chills.

"What we've been having for the last several weeks now has been a jet stream that's gone way up to the north over Alaska and the Arctic, and then come plunging down over the central U.S. and into the East," Mr. Martin said.

Arctic air

"It's brought with it cold air from right over the Arctic to right over us," he said.

Arctic air with wind chills down to 74 degrees below zero swept across the central and eastern United States yesterday in the wake of a blizzard that dumped up to 2 1/2 feet of snow and paralyzed much of the Ohio Valley.

Maryland got a nasty mixture of snow, freezing rain, rain and ice.

The jet stream -- a fast-moving river of high-altitude winds -- steers ground-level weather systems. In most winters, its undulating path would take it north into Canada and about as far south as Washington.

But in some years, its "amplitude" increases, pushing its northernmost bend farther north -- where it gathers up arctic cold -- and its southernmost bend farther south, where it delivers frigid weather to unprepared southern states.

After decades of study, scientists have noticed correlations between these unusual changes in the jet stream and periodic changes in water temperatures and air pressures in the Pacific Ocean.

"The kind of pattern we've seen recently is frequently associated with the warm phase of the El Nino and southern oscillation phenomenon," Mr. Martin said. Scientists refer to the combined phenomena by the acronym ENSO.

El Nino -- Spanish for "the child" -- is a warming of ocean waters west of South America. It was named by the Spanish, who noted that it appeared around Christmastime and chased away coastal fish that prefer colder water.

The "southern oscillation" is a shift in atmospheric pressure patterns between Australia and Tahiti.

"We've recently come out of what's called the warm phase of ENSO . . . and frequently we find that when we come out of a weak warm phase, it's associated with this kind of atmospheric jet stream pattern that brings real cold arctic outbreaks to the eastern U.S."

It's even more strongly associated with a strengthening of the sub-tropical jet stream, which brings moisture out of the tropical Pacific across Mexico, delivering above-normal precipitation to the Gulf Coast and the southeastern United States.

Where the tropical moisture collides with cold arctic air, it snows.

Warmer days expected

Sometimes the outbreaks can persist for a month to six weeks. Other times they are over in two weeks.

Mr. Davis noted that after the January deep-freeze in 1977, February and March were warmer than normal. The four next-coldest Januarys -- all since 1961 -- have been followed generally by warmer-than-normal weather in February and March. So "this January doesn't portend doom for February and March," he said.

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