The back-to-back-to-back snow storms over the past few weeks have given rise to a near nightly festival of numbers: The current snow totals. The total totals. The historic totals. But just where exactly are all these numbers coming from? And how do we know they're right?
"A lot of people think, 'You wanna measure snow? Go ahead and stick a ruler in the snow and then you'll get it," said Alan Dunham, the leader of the observer program for the National Weather Service’s area forecast office in Taunton. "And actually it's a lot more involved than that. We had to come up with a way of standardizing how snow was measured."
Years back, at a huge conference in Colorado, the weather community — writ large — did just that. Here’s the drill.
"You need a snow board," Dunham said. "Which is just a 2-by-2 piece of plywood — it can even be a little bigger or a little smaller. Painted white."
That’s so it doesn’t absorb any heat that could melt down any of the snow. Before a snow event, you clear your board.
"It was decided through a lot of empirical data that the best way is to measure your snow on the board every six hours, and then clear the board," Dunham said. "And then six hours later measure your snow again."
Wait any longer, and the snow will start to compact, leading to an underestimate. Clear it too often, it doesn’t settle at all, and you get an overestimate. Heck, they’ll even melt down the snow and analyze the water content.
"For all the sites that we have direct control over — so, the cooperative observers and at the individual weather offices — that’s the procedure that they follow," Dunham said.
But that only accounts for a handful of locations. And yet the National Weather Service is swimming in data, with snow totals from every nook and cranny of the region, from Adams to Yarmouth. Soooo …
"We have between 5,000 and 6,000 volunteer weather spotters," Dunham said.
Volunteers, but not untrained. Tim Miranda is one of those SKYWARN spottersfor the National Weather Service. A self-described life-long weather geek, Miranda stumbled on the spotter program on the Internet a few years back and signed up for class.
"I had no idea what it would be and I said, 'Oh this is free,'" Miranda said. "It was on a weekend. I showed up on a Saturday morning. And there were just all different kinds of people there. High-school kids to retired folks. And it just seemed exciting."
His weather center? His backyard in North Chelmsford. Spotters like Miranda can’t operate with the precision of the weather centers, but they’re encouraged to get close.
"My board is buried," he said. "I have a flag to mark it."
He’s been trained to clear it as close to every six hours as possible. And to account for drifting – he’s trained to take multiple measurements, then average them out.
Back at the office, Dunham says they keep a close eye on the numbers coming in.
"We have to do some quality control to weed out what is best called bogus reports," he said. "And they pretty much stick out."
Dunham says that on average, 150 to 250 of their spotters file data each time it snows. It’s those numbers that feed the newswires and weather broadcasts. But that’s not all.
"The data gets sent down to the National Climactic Data Center," Dunham said. "They certify all the weather records for the entire country. And they get requests in all the time."
From municipalities applying for state money to researchers studying climate change to insurance companies investigating claims. All that, thanks of thousands of volunteer citizen scientists like Miranda.
"It’s nice to see that this hobby that I was already into is actually useful to someone else besides me, that’s kind of cool," he said.
It’s time to clear your board again, Tim. As I’m sure you’ve heard, there’s yet another storm coming.
If there is something you are curious about, email Edgar at curiositydesk@wgbh.org. He might just look into it for you.
