Mild winter gives way to spring tonight

March 20, 1991|By Luther Young

The arrival of spring at 10:02 tonight officially caps one of the most unexpectedly mild winters in decades, embarrassing long-range forecasters at the National Weather Service as well as groundhogs, woolly bear caterpillars and almanac prognosticators.

At Baltimore-Washington International Airport, the average temperature of 39.5 degrees for the three-month "winter" season -- December, January and February -- was the warmest in 40 years of record-keeping, beating out a previous record set in the winter of 1974-1975.

And snowfall totaled a paltry 9.6 inches at BWI through yesterday, with only 0.1 inch in February, usually the area's snowiest month at an average 6.9 inches.

Accumulation for a winter in Baltimore is normally 21.6 inches.

"Our forecast was flat wrong. We knew by Christmas it was a dead duck," said senior seasonal forecaster Robert Livezey at the weather service's Climate Analysis Center, referring to the 90-day long-range winter forecast issued in late November.

That prediction -- based on global atmospheric and ocean temperature measurements fed into complex computer models -- called for a 60 percent to 65 percent chance of colder-than-normal temperatures in the eastern United States. A percent chance represents the accuracy of a coin toss.

Fickle Mother Nature didn't cooperate.

Not a single low-temperature record was broken this winter at the NWS station at BWI or the downtown monitoring station in the Custom House, although five heat records fell during February.

At the airport, where record-keeping began in 1951, new highs were set with 65 degrees Feb. 3, 72 degrees Feb. 4 and 73 degrees Feb. 5. At the Custom House, temperatures of 67 degrees Feb. 3 and 69 degrees Feb. 4 broke records for those dates going back 120 years.

February's average temperature at BWI was 40.7 degrees, 6 degrees above normal, said NWS forecaster Amet Figueroa.

January finished 2.8 degrees above normal at 35.5 degrees, and the March average temperature through Monday was 44.0 degrees, about 0.7 degrees above normal.

December was almost tropical compared with the same month a year earlier, when the average temperature plunged more than 11 degrees below normal. This winter, the last month of 1990 was 5.7 degrees above normal at the airport at 42.2 degrees.

"It was not one of our better efforts" since the 90-day forecasts began in 1958, said Dr. Livezey. He estimated its accuracy nationwide at

40 percent to 45 percent, well below the historical average accuracy of 65 percent and even worse than a coin toss.

What went wrong? Back in November, NWS forecasters bet the farm on the expected appearance of a mass of warm water in the central equatorial Pacific Ocean that historically has strongly influenced North American winter weather.

The warm surface water -- part of a little-understood phenomenon known as the Southern Oscillation -- sets up huge convection systems in the atmosphere that can distort the normal winter patterns of the high-altitude jet stream moving across North America and permit frigid Arctic air to surge down into the East.

"Usually, in late November, we've known pretty decisively if it was going to happen," Dr. Livezey said. "This year, it was right on the edge, and we went the wrong way. It just didn't materialize" for still unexplained reasons.

In his agency's defense, NWS forecasters recovered some of their self-respect with their 90-day forecast at the end of December, calling for a 57 percent chance of above-normal temperatures during January, February and March in Maryland.

And, as Mr. Figueroa pointed out, the public reaction to the failed forecast could have been much worse. "When people think it's going to be a severe winter and it's not, they're happy," he said. "It's the other direction where you've got a real problem."

Climatologists say such short-range changes in weather cannot

be scientifically tied to global warming, the widely predicted rise in world temperatures caused by polluting gases that trap heat in the Earth's atmosphere.

But our mild winter followed a year, 1990, which was the warmest in 120 years of official records in Baltimore and Washington.

It was also the third-warmest year on record in the lower 48 states and the hottest worldwide since widespread record-keeping began in the 19th century.

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