A likely record, but experts will get back to us

Measurement problems prevent meteorologists from saying for sure

February 06, 2010|By Frank D. Roylance | frank.roylance@baltsun.com

The powerful nor'easter that buried Central Maryland in more than 2 feet of snow Friday and Saturday will be ranked among the biggest in the region's weather annals. But meteorologists at the National Weather Service were unable to say Saturday precisely how much snow fell. Problems with measurements at Baltimore-Washington International Thurgood Marshall Airport have left Baltimore without an official tally.

Preliminarily, the NWS estimated 24.8 inches fell at BWI during the two-day storm, exceeding the 24.4 inches that fell there over two days in February 2003. It fell short of the all-time, two-day Baltimore record of 26.3 inches set downtown in January 1922.

"I'm feeling pretty comfortable saying we broke a two-day snowfall record" at BWI, said James Lee, meteorologist in charge at the Baltimore-Washington Forecast Office. But "it will take several days to work with climatologists to make something like that official."

Apparently, there are two problems.

The first appears to lie with a contract weather observer at BWI who evidently failed to follow official NWS procedures. The second involves how much of the four-day 2003 storm that currently holds the No. 1 spot at BWI should be counted as official.

Official snow measurements for the weather service are supposed to be made every six hours. Then the "snow board" is supposed to be wiped clear, and new measurements are taken in six-hour intervals until the storm ends. The totals are added.

Unfortunately, Lee said, "We don't have an observation for every six hours." Instead, the observer for this storm took two measurements. One is called the "snow depth," which measures all the snow that fell, all at once. That was reported as 24.7 inches, Lee said.

The second was the total of measurements taken every hour on the hour. That total came to 28.6 inches.

The problem, Lee said, is that the "snow depth" method allows the snow to compact, producing a low figure. The hourly measurements eliminate most compaction and exaggerate the total on the high end.

Then there's the issue of what number to use for the current No. 1 snowstorm on Baltimore's record books.

Everyone agrees that was the storm that struck Feb. 15-18, 2003. The total snowfall for that four-day period was 28.2 inches. The statistic is listed on the weather service's Sterling, Va., Web site as the biggest storm in the city's history.

But Lee said that snowy episode was actually two storms, so "that needs to be ignored; all that is is 'What four consecutive days gave Baltimore the most amount of snow?' We don't recognize that."

The official arbiter of such things is the National Climatic Data Center, which only counts snowstorms lasting one, two or three days.

For purposes of calculating the official record, Lee said, the forecast office is focusing on two days of the 2003 snowstorm -- Feb. 16-17. That total comes to 24.4 inches at BWI.

Even if they had taken the compacted "snow depth" measurement from BWI on Saturday, the Super Bowl Weekend Storm of 2010 would beat that two-day total from 2003 by three-tenths of an inch. Hence Lee's confidence that this storm is likely the biggest ever among BWI totals. The 1922 storm measured snow totals taken downtown.

However all that's eventually resolved, everyone agrees it was a heck of a snowstorm.

A week of escalating forecasts from the National Weather Service and others had pushed the projected snowfall from 6 inches to 12 inches on Tuesday to an impressive 20 to 30 inches by the time flakes began to fall. Some forecasters pointed to the tremendous moisture content of the approaching storm and speculated about totals above 3 feet.

The storm began before noon Friday in Baltimore as a deep low-pressure system moved across the South, drawing moisture from the Gulf of Mexico and sending it into the Northeast.

For more than five hours, the fine but steady snow refused to stick to the streets. Surface temperatures hovered above the freezing mark. Schools were closed early, long before the roads might have justified the lost instructional hours. Traffic was sparse.

But by 6 p.m., temperatures began to fall toward 32 degrees. City streets became snow-covered and interstate traffic slowed as slush and snow built up and traction diminished.

Overnight, temperatures dropped into the upper 20s and, as the storm intensified, snow accumulations began to accelerate. Marylanders awoke to a softened landscape and impressive snowy heaps where their cars once gleamed. And heavy snow continued to fall.

The National Weather Service said snow totals on Friday and Saturday broke records for those days in Baltimore and Washington.

For Baltimore, the 7.5 inches that fell before midnight broke the old record of 6.4 inches for a Feb. 5, set in 1899. The old Feb. 6 record was 8.4 inches, set in 1978. Also erased.

At Washington's Reagan National Airport, the 8.7 inches that fell on Friday broke the old record for Feb. 5 of 7.5 inches, set in 1892. The old record for a Feb. 6 snowfall in the capital was 4.4 inches, set in 1983. That record, too, was topped.

There is another superlative that can be applied to this snowstorm. NWS meteorologist Jared Klein said this is the first winter on record in which Baltimoreans have endured two storms that each dropped more than 20 inches of snow.

One other question that still can't be resolved, however, is whether this was truly a blizzard. Although blizzard warnings were posted, it was not immediately clear whether the requisite conditions were fulfilled: three or more hours of falling or blowing snow, with winds more than 35 mph reducing visibility to less than a quarter-mile.

"We haven't had time to analyze that, either," Lee said.

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