Meteorologists are apt to say that estimating snow accumulations remains one of their most elusive exercises. Evidently that's the case even after the snow stops.
For the second time in less than two weeks, an official snowfall total at Philadelphia International Airport has been revised.
At 1 p.m. Thursday, the National Weather Service's newly hired snow-observing team reported that 0.8 inches had fallen at the airport site.
Even though the snow in Philly sank far beneath expectations of 6 to 10 inches, some skeptical observers questioned whether it could have been that far beneath.
Among them was Tom Fulmer, a honcho at the phillywx.com chat board. After looking at visual evidence on I-95 traffic cameras near the airport, he appealed to the National Weather Service Office for a review.
On Friday, the weather service bumped up the total to 2 inches.
"We basically looked at all reports within the Philadelphia area to get an overview of how much snow fell, and where, to determine the overall pattern of the snowpack," said Joe Miketta, acting chief of the Mount Holly office.
The airport total evidently was out of sync. A 2.8-inch total was reported from West Philadelphia, and there was 2.3 in National Park, directly across the river from the airport site.
Miketta said he believed the wind – a gale-force 39 mph gust was reported – might have blown snow from the measurement board.
"The airports are the absolute worst place to measure snow," said Tony Gigi, a retired weather service meteorologist who has been a snow observer at airports in the New York City area.
Airports are wide open to the wind, not to mention the disturbances caused by aircraft taking off and landing.
Yet since aviation began, they have been popular sites for official weather measurements.
Miketta said he had no issue with the team of measurers, employed by a company located at the airport. They were hired before the winter to replace the former observer, who was stationed in National Park.
The weather service trained them in the art of snow measurement, for which the government has a 14-page instruction manual. Essentially, they measure on a "snow board," a square white piece of wood placed in an open area.
Seems simple enough, but snow-measurement controversies are nothing new. It took a few years to affirm that 30.7 inches of snow had really fallen in Philadelphia on Jan. 7 and 8, 1996.
Most recently, a 0.1 inch total for a Jan. 30 snowfall was reviewed and bumped up all the way to 0.8.
"Snowfall measurement," said Miketta, "is not an exact science."