Coming: Relative warmth

February 20, 2007|By Dennis O'Brien | Dennis O'Brien,Sun Reporter

No one is saying that winter is over. But with the official start of spring a month away, temperatures are expected to climb into the 50s over the next few days - so it might begin to feel that way.

We could see some snow showers, forecasters say, but the warming trend is supposed to last for at least the next week or so, bringing above-average temperatures to replace the frigid weather of the past month.

"Is it going to give us false hope? It might. But the fact is that there's no cold weather expected in the immediate future," said Marisa Ferger, a meteorologist with Penn State Weather Communications Group in State College, Pa.

We can expect normal temperatures - that's a high of 45 degrees this time of year - and even some above-normal temperatures for at least the next week, forecasters say.

Beyond that, "It's really hard to say how long it's going to last," said Alan Reppert, a meteorologist with Accuweather in State College, Pa.

Forecasters blame the cold snap on - and credit this week's warming to - a shift in the jet stream that has kept frigid arctic air in Maryland since mid-January. When the jet stream moves south, it prevents warm air from flowing into the area. When it shifts north, which appears to be happening now, it opens the way for milder temperatures.

"It was a stubborn system overall, and for the longest time it wouldn't let any warm air from the south come in at all," Ferger said. "Finally, it went north where it belongs."

The very low temperatures seemed all the more severe because of the warm spell that preceded them. December's average daily temperature was a relatively balmy 42.4 degrees, about 6 degrees above normal. The warmth continued into early January, when daily highs spiked above 60 degrees seven times in the first 16 days, hitting 71 degrees on Jan. 6.

But all that changed with a freeze that arrived aboard an arctic blast in mid-January. On Jan. 17, the average temperature dropped to 28 degrees - 19 degrees colder than the day before.

Average daily temperatures haven't hit the 40s since. So far this month, the average has been a chilly 25 degrees - 10 degrees colder than normal for February.

To find a similarly cold February, you have to go back to 1979, when the monthly average dipped to 25.6 degrees.

The warmth is expected to thaw much of the 2.7 inches of precipitation that fell in a mixture of rain, sleet and snow over two days last week. The cold and storm also broke water mains in Baltimore and knocked out power to thousands across the state.

Forecasters say they don't expect flooding to be a problem - the melting will be gradual and there isn't that much snow to melt. So far, the February snowfall has been only 4.2 inches; far more would be necessary to create flooding, experts say.

"I think the streams can accommodate it because they're at normal or below normal levels for right now," said Wendy McPherson, a hydrologist with the U.S. Geological Survey in Baltimore.

But that assumes water can get to the streams in the first place. Baltimore public works officials asked residents yesterday to clear storm drains of branches and other debris to prevent potential backups of runoff.

City crews are still working to repair some water mains damaged by the cold spell, but most have been fixed, said Robert Murrow, a public works spokesman. No major flooding is expected in the city, he said.

Baltimore's water mains cover the city and portions of Baltimore County. They include about 3,400 miles of main pipes, some more than a century old. Most of the pipes that eventually fail do so because they expand and contract with variations in temperature, city officials said.

The thawing of frozen ground also can shift soil, putting strains on the mains and causing pipes to crack, Murrow said.

But that isn't expected this week because temperatures aren't expected to climb that drastically, Murrow said.

"I think we're going to be OK," he said. "I think we've been through the worst."

dennis.obrien@baltsun.com

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