December snow, and season, lose 3 inches

The winter of 2009-2010 will still go down in the history books as the snowiest on record for Baltimore. But in the end it will be three inches less stupendous than we thought.

Meteorologists at the National Weather Service have just finished adjusting their snow tallies to account for measurement problems at BWI-Marshall Airport. Officially, at least - the winter delivered 77 inches, not 80.2 inches as the weather service first reported.

And the big storm in December will be recorded officially as an 18-inch snowfall, not 21.1 inches as the first reports stated. December's monthly total has been similarly reduced from 23.2 inches to 20.1 inches, according to the Baltimore-Washington Forecast Office in Sterling.

The changes don't affect any of the records broken in December. The Dec. 18-19 snowstorm remains the biggest December snow on record for Baltimore, and the month remains Baltimore's snowiest December.

And even at a mere 77 inches, it's still the snowiest winter on record for the city. The annual average for Baltimore is 18.2 inches.

The reduction in some winter snow totals was made late last week as Sterling reviewed each of the season's snowfalls to adjust for measurements that were not in compliance with the weather service's protocol.

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Until the problem was discovered in the wake of the Feb. 5-6 blizzard, contract observers working for the Federal Aviation Administration were making only hourly snow measurements, and taking storm totals after the flakes stopped falling - called "snow depth" measurements.

The technique, which complies with FAA rules, is considered invalid by the NWS for climatological data, because it does not allow the snow to compact.

The weather service requires that snow measurements for climatological purposes be made one every six hours. Because of compaction, the totals are usually smaller. That's what the FAA contractor was supposed to have been supplying to the weather service.

So, with no six-hour data, Steve Zubrick, Sterling's science and operations officer, elected to use the FAA's snow depth data instead of the hourly measurements, because it is the most conservative solution.

He and forecaster Jared Klein combed through the data and made the changes. Some snowfalls were unaffected. Most turned out smaller. A few increased due to rounding of snow depth numbers to the nearest inch.

Here are the original and revised numbers for BWI:

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December: Original: 23.2 inches Revised: 20.1 inches

January: Original: 7.5 inches Revised: 6.9 inches

February: Original: 49.5 inches Revised: 50 inches

Season: Original: 80.2 inches Revised: 77 inches

Major storm totals:

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Dec. 18-19: Original: 21.1 inches Revised: 18.0 inches

Feb. 5-6: Original: 24.8* inches Revised: 25 inches

Feb. 9-10: 19.5 inches (no change; measured properly)

* This was the original snow depth measurement. The FAA's total from one-hour measurements was 28.8 inches.

(SUN PHOTOS: Top: Algerina Perna/Bottom: Karl Merton Ferron)

December snow, and season, lose 3 inches

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