‘Good enough’ measuring technique
To begin, if possible, it is best to avoid measuring on the grass. Air caught in between tall blades will add extra accumulation. The last thing you want to be known as is a snow exaggerator. But, if you have no choice, measuring on low-trimmed grass is okay.
Flat and level surfaces are preferable. Wood is probably the best, but picnic tables, car tops or flat trash can lids also work.
Pay attention to potential obstructions in and around your measurement spot. You don’t want to measure under a tree, which can intercept snow. Also try to find spots some distance away from buildings that can influence amounts by blocking or funneling wind. For this reason, decks adjacent to homes can be a problem, even though they’re otherwise good surfaces for measuring.
Once you find an undisturbed spot, or several, you’ll want to take at least a handful of measurements. The more the merrier, but three to five should be enough. Try to round amounts to the nearest tenth of an inch, but a quarter-inch works in a pinch.
After you’ve taken at least three solid measurements, average them to determine your total.
Measuring like a pro
Even if you’re a hobbyist, it’s easy to measure like a pro.
Official measurements logged into the National Weather Service records are typically done with a snow board — basically a square piece of wood, placed flat on the ground.
Place the snow board before the storm. Perhaps mark it with a flag or stake so it’s easy to find once buried.
You’ll want to make sure the snow board is not close to obstacles that may interfere with the snowfall. Placing it at least 10 feet from fencing, trees or structures is wise, as is trying to find areas with minimal drifting.
The snow board standard is to measure once every six hours, then clear it to allow new accumulation, then sum each measurement. This method is considered most accurate, because over longer periods the weight of additional snow leads to compression and lowers totals. Clearing more frequently than every six hours is frowned upon, as it will inflate totals.
Often, storms don’t cooperate by ending on the six-hour mark. If snow ends or changes to mixed precipitation during the course of a storm, it’s best to get a measurement as soon as possible once accumulation ends. You want to take the maximum total on the ground, before a change to rain, settling of the snow or melting.
Snow measurement controversy
Sometimes, in reports of snowfall totals on social media or even the National Weather Service, you might encounter an amount that differs from most of the others.
Invariably, some people inflate or underestimate snowfall totals because of improper measuring. Outliers should be treated with suspicion, although significant differences sometimes happen over a small area when very localized heavy snow bands develop.
It’s not just amateurs who sometimes post questionable amounts. Take the Reagan National Airport official measurement during the January 2016 blizzard dubbed Snowzilla. It reported 17.8 inches from the storm four hours before it stopped snowing but submitted that number as the final storm total, even though additional snow had fallen.
The Washington Post learned that the weather observer at the airport lost the snow board during the storm and that the final number simply reflected the amount on the ground when the storm was over, rather than the sum of six-hour snow board measurements. In a post-storm review, the Weather Service conceded the measurement method used was “not ideal” but did not make adjustments to the 17.8-inch number.
During the same storm, the Weather Service discovered that observers at Newark Airport had summed snow totals hourly (rather than the standard six hours), wiping the snow board clean after every observation, inflating totals. It decided to lower the initial snowfall report of 28.1 inches to 24.5 inches after a post-storm review.
The value of snow measurements
While it may seem like “it’s just snow, so what?” reliable snowfall measurements are important for historical records and may even determine whether relief is sent to a location after a major storm. They are also extremely helpful for storm tracking and verifying the accuracy of forecasts.
After taking snowfall measurements, send them to the National Weather Service forecast office serving the Washington/Baltimore region and to the Capital Weather Gang through our blog or social media accounts.