The near-record snowfall total recorded at Reagan National Airport during the January blizzard will stand, the National Weather Service said Thursday, despite a measuring mishap that called into question whether the tally was too low.
Agency officials who conducted a three-month review said the method used to measure the snowfall at D.C.’s official recording site was “not ideal” but said the 17.8-inch total was accurate, based on a comparison with unofficial tallies in nearby locations.
The agency’s report, however, recommended changes to prevent the kind of problems that occurred at Reagan National and other official observation sites between D.C. and New York City during the massive storm.
The snowfall measurement at Reagan National Airport came under scrutiny after The Washington Post reported the weather observer there lost a board used to measure snowfall and had to improvise midway through the storm.
Observers were unable to locate the board because it was buried in the snow, forcing them to switch to a different method that experts have said could lead to lower totals.
The report issued by the National Weather Service team did not address the effect of inconsistent methods and instead found that the loss of the board was “reasonable” given the weather conditions and amount of time between each measurement.
“The [snow board] was buried under the snow, and this is reasonable given the six-hour period between official snow depth measurements,” the report states.
Observers use snow boards to measure accumulation every six hours. After each measurement, snow is cleared for the next measurement. The numbers are added for a total accumulation. This method is considered more accurate because over longer periods the weight of additional snow leads to compression and lower totals.
In an interview, the review team’s co-leaders acknowledged that they did not interview the weather observer who lost the snow board. Instead, they spoke with his boss during a tour of the observation site. They also reviewed the observer’s logs from the storm.
“The actual observer was not there when we did the tour,” said Andy Horvitz, a National Weather Service meteorologist and co-lead on the report. Horvitz said they spoke with Mark Richards, the observer’s manager.
Weather observers at the two other major airports in the region follow National Weather Service snow measurement guidelines; however, the observers at National are contracted by the Federal Aviation Administration and are required to follow FAA guidelines.
Though the review did not fault the measurements taken the night of Jan. 23, it does recommend attaching flags to the snow board so that it can be more easily located in deep snow. The Weather Service team said that the use of flags, while not required, is a “best practice.”
Flags and boards aside, the timeline alone suggested that something was amiss on the night of Jan. 23.
At 8 p.m. Saturday, 17.8 inches of snowfall was reported by the observer at National. It reflects a 0.3-inch increase in the three hours between 5 and 8 p.m., when light to moderate snowfall was being reported by the automated weather system at the airport. The total also reflects zero snow accumulation in the four hours after 8 p.m., though the observer continued to report snow was falling. This timeline suggests a higher total should have been reported between 5 p.m. and midnight.
Jim Zdrojewski, a co-leader on the report, said that the automated observations were “potentially” incorrect.
“One thing to understand is that those conditions are being taken by an automated system right near the runway in the most exposed area possible on an airport,” Zdrojewski said. “We’re looking at what the conditions were … and looking at the radar and the synoptic situation at that time in the early evening and the bottom line is there were strong winds and it was snowing so lightly.”
Bob Leffler, a retired National Weather Service climatologist, is the author of the National Weather Service’s snow measurement guidelines. After the blizzard, Leffler told The Washington Post that failing to clear the snow board every six hours could have resulted in a 10 to 20 percent reduction in final snowfall.
Studies agree. One experiment that measured snow in 28 storms found that clearing the snow board every six hours led to a 19 percent increase in snowfall total.
Significantly higher snowfall totals were reported at the region’s two other airports. Washington Dulles International recorded 29.3 inches, while Baltimore-Washington International Marshall Airport recorded 29.2 inches.
Teams at both of those airports continued to use and clear snow boards every six hours despite the snowy, windy conditions, as required by National Weather Service guidelines.
They are also in typically cooler and higher locations than National, which usually contributes to the higher totals.
As it stands, the storm ranks as the fourth-snowiest on record at National. Records for this location go back to 1871.
The report examined practices at eight climate-reporting sites from the District to New York, finding all snowfall totals were correct and guidelines followed at every location except for Newark Airport and New York City’s Central Park.
At Central Park, the review team found that a miscommunication between the local Weather Service office and the weather observing team led to an incorrect snowfall report. When the storm ceased, the National Weather Service reported a snowfall total of 26.8 inches — one-tenth of an inch shy of an all-time greatest snowfall record. The Central Park Conservancy actually measured a total of 27.5 inches, a new record.
At Newark, the team found that weather observers cleared the snow board too often — every hour — which resulted in an inflated snowfall total, and a false preliminary all-time record of 28.1 inches. They also found that observers may have been using this practice since 1996. The team will look into the historical record of snowfall reports at Newark to determine if any measurements should be changed. A separate team will look into the possible revision of the Newark snowfall total in the blizzard itself.
Jason Samenow contributed to this report.
This story has been updated.