A Wintry Ending To City's Wettest, Snowiest Dec.?

Storm May Bring Freezing Rain, Snow New Year's Eve

December 30, 2009|By Frank D. Roylance | Frank D. Roylance,frank.roylance@baltsun.com

At the tail end of the wettest and snowiest December on record, and topping off one of the city's wettest years, it looks like the area is in for more rain and snow before ringing in the new year.

The National Weather Service is forecasting a 60 percent chance for a "wintry mix" of precipitation on New Year's Eve, continuing through the night.

The area might see sunshine today, but the bad weather is expected to start as snow after 1 a.m., changing to freezing rain and then rain by Thursday afternoon.

Forecasters say they're not expecting a big, snowy finale to the year. But "this is a tricky one," said Brian Lasorsa, a meteorologist with the National Weather Service's Baltimore-Washington forecast office in Sterling, Va.

"I don't think it will be nearly as disruptive as the last one," he said. "I think precipitation amounts will be light, with the biggest impact overnight Wednesday into Thursday. ... The biggest hazard will probably be freezing rain."

December 2009 is already the wettest December in 138 years of record-keeping for Baltimore, with 7.67 inches of liquid precipitation through Dec. 29. That beat the previous record of 7.44 inches, set in December 1969. The December average is 3.35 inches.

The 21.1-inch snowstorm on Dec. 18-19 also made this the city's snowiest December on record. Through Monday, a total of 22.2 inches had fallen at Baltimore-Washington International Thurgood Marshall Airport. The previous December record was 20.4 inches, set in 1966. Average December snowfall at BWI is 1.7 inches.

It's all a climax to an extraordinarily wet year. More than 55 inches of rain and melted precipitation have fallen at BWI since Jan. 1, topping the average of 41.94 inches by more than a foot.

After a dry start to the year and a brief drought declaration in late March, the heavens opened up. Since April, only two months - July and September - failed to top long-term averages.

Lasorsa blames "a more active southern branch of the southern jet stream," something typical in years like this one in which El Nino events take shape in the tropical Pacific Ocean.

El Nino is a periodic warming of the sea-surface temperatures in the central and eastern Pacific. The more active jet stream sends more storm systems tracking across the southern United States.

"They have a lot more moisture to tap into from the Gulf [of Mexico], the Gulf Stream and the Atlantic. That adds moisture and brings more precipitation," Lasorsa said.

Forecasters expect the high-pressure system that brought sunny skies Tuesday to begin moving off the mid-Atlantic coast today. That will put the area in a return flow of air around the west side of the system, drawing milder, wetter air in from the South.

Light precipitation will spread across our region after midnight, falling initially as snow as it encounters the cold air that has been pouring into the region on strong north winds all week.

Then, another low-pressure system developing over the northern Gulf of Mexico will move off the Carolina coast tonight into Thursday.

What follows will depend on the storm's timing and speed as it intensifies and tracks up the coast and how much cold air it can draw back into the area from the north.

"I don't think it comes together until [the storm reaches] southern New England," Lasorsa said. But "if it develops closer to the mid-Atlantic coast ... it could have an impact on our forecast," meaning more frozen precipitation.

For now, the precipitation is likely to change to freezing rain and then all rain during the day Thursday and finally back to snow overnight Thursday into Friday - New Year's Day.

Baltimore's wettest years ...

2003: 62.66 inches

1889: 62.35 inches

1979: 58.98 inches

1996: 58.31 inches

1952: 56.57 inches

2009: 55.18 inches*

Average: 41.94 inches

... and wettest Decembers

2009: 7.67 inches*

1969: 7.44 inches

1936: 7.10 inches

1901: 7.07 inches

Average: 3.35 inches

* Through Dec. 29

Source: National Weather Service

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