Depth of two-day snowfall remains blanketed in mystery

  • Shawn Durkin, weather station manager who has worked for Pacific Weather Inc. for 16 years, stands on the rooftop location at BWI where Pacific Weather takes its snow measurements, using a snow board, mounted on the bench to his left, and an 8-inch rain gauge, at right.
Shawn Durkin, weather station manager who has worked for Pacific… (Baltimore Sun photo by Amy…)
February 20, 2010|By Frank D. Roylance

The blizzard that heaped more than 2 feet of snow on Baltimore on Feb. 5 and 6 was probably the deepest two-day snowfall on record. But we might never be sure how deep it was.

A contractor working for the Federal Aviation Administration at BWI Thurgood Marshall Airport, paid to measure the snow for the aviation industry's needs, did not follow a separate protocol required by the National Weather Service and the National Climatic Data Center for valid climate data.

So while the contractor measured 28.8 inches of snow during that storm, the National Weather Service has thrown out the reading. Instead, climatologists will rank the storm as "only" 24.8 inches - a number that almost surely understates the "true" total.

Worse, for climatologists, it now appears the weather service's rules for snow data had been ignored for years at BWI, throwing a cloud over the validity of snow totals as far back as 1998, when the FAA took the job over from the weather service.

Only BWI's data are known to be affected, but the problem could be more widespread. That possibility has caught the attention of top officials at the FAA.

"We plan to meet with the National Weather Service next week to begin a discussion on making sure that we're all on the same page in terms of measuring snow accumulations at our airports," FAA spokesman Jim Peters said. "There will be a national discussion."

In the meantime, the weather service's Baltimore- Washington Forecast Office in Sterling, Va., is preparing to convene a committee of climatologists and other experts to review Baltimore's snowfall records from the 2010 and 2003 storms, and perhaps back to 1998.

"I feel very strongly about historical records and getting the climate data correct," said James E. Lee, the meteorologist-in-charge at Sterling. "Obviously, with the increased media attention and political attention to climate, it is really up to NOAA [the National Oceanic and Atmospheric Administration, of which the National Weather Service is an agency] to make sure ... the climate record is a genuine one, and consistent to the best of our ability."

The problem at BWI came to light Feb. 6, as snow accumulations reported at the airport passed 26 inches. They seemed poised to break the record set in February 2003 - the storm listed on Sterling's Web site as Baltimore's biggest.

But when reporters called asking about a new record, Lee said that because of measurement errors by an FAA contractor at BWI, the two-day storm total would be pegged at "only" 24.8 inches. He had discarded a 28.8-inch measurement from BWI because it was the sum of hourly measurements throughout the storm - a method invalid for climatological data.

Even at 24.8 inches, Lee said, the storm total beat the previous two-day record of 24.4 inches, set at BWI during two days of the four-day 2003 event. "I'm convinced that was the most amount of snow Baltimore has seen [from a two-day storm] in recorded history."

But Lee had to use the most conservative reading from the airport - a "snow depth" measurement of the total on the ground when the storm ended, after hours of compaction.

The FAA requires its observers to take hourly snow measurements and wipe the boards clean after each hour, adding the totals as they go. That provides pilots with better real-time information about changing conditions. But it virtually eliminates compaction and so inflates accumulation. Climatologists require measurements every six hours, striking a balance between the hourly and snow depth readings. Some airports maintain separate snow boards for the different protocols. But not BWI.

Richard Carlson, vice president of Pacific Weather Inc., said his company has experienced weather observers at 20 U.S. airports, including eight at BWI. Pacific has held the contract there since 2008.

"We follow the FAA manual ... and that is the guide book on how these meteorological observations are to be taken," Carlson said. "We had heard about the six-hour measuring thing, but ... if you have high winds at all, this really is not going to work."

So when Lee questioned the snow data from BWI on Feb. 6, Carlson said, "we informed them [Lee] that we have different criteria, a different manual we are following." He says the company's predecessor at BWI also followed FAA rules.

Lee "kept harping back to the six-hour measurement thing," Carlson said. "That's meant for climatological purposes, and what we're doing is operational," serving the needs of the airport. "He wasn't real happy."

Lee wasn't happy, but there was little he could do. "It's interesting to have the responsibility for quality control but not the authority to tell the [FAA] contractor what to do," Lee said.

"In future inspections, this will be raised ... prior to the start of the winter season, to ensure the six-hour swipe is going to be adhered to," he said.


> Read Frank Roylance's blog on MarylandWeather.com

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