The National Weather Service has clear guidelines on how to measure snowfall for one simple reason: snowstorms have a huge effect on the economy, life and property. They have an impact on millions of people and can result in millions of dollars lost. They also play an obvious important role in the historical record.
The way that the snowfall has been measured at National in this storm has led to snowfall totals that could be much lower than what has actually fallen and may have unnecessarily withheld the storm from ending as one of the top 3 snowiest on record.
Snowfall is a very difficult thing to measure. The best way we have, and the way that the National Weather Service suggests, is with a snow board. The board is placed on the ground before the storm starts in a location that will be undisturbed by drifting. When the storm starts, snow is periodically measured, and the board is wiped clean.
If the board is not wiped clean before the next measurement, compaction can occur because of the weight of the snow, and the measurement will be lower than what has actually fallen.
The measurements taken at National were not done with a snow board, so they may have been reduced by compaction.
Jim Lee, the meteorologist in charge at the National Weather Service in Sterling, Va., told The Washington Post that he agrees that if the snow hasn’t been measured by the guidelines, the totals are “perishable.” Lee noted that in any storm, the observations are preliminary until they can survey it and make it official.
If the storm is potentially record-breaking – say, in the top 10, like this weekend’s storm is – the Weather Service turns to the National Climatic Data Center to run the observations through quality control.
Though Lee’s team was and will continue to be in the midst of an emergency situation Saturday night, he assured us that they will begin to look into the data as soon as the storm allows.
Jason Samenow contributed to this post.
An earlier version of this story incorrectly said the Weather Service contracts with the FAA for the observations. The contract is actually between the FAA and the observers.