Good Question: How Do We Measure Snowfall?
MINNEAPOLIS (WCCO) -- The official National Weather Service tally for the MSP airport for our February snowstorm is 9.4 inches. But, chances are, if someone stuck a ruler in the snow this morning, they'd find something different. Wind can throw those numbers way off.
So Ken from Fridley and John from Jeffers want to know: How is snowfall officially measured? Good Question.
The National Weather Service (NWS) uses the same method it's used for 70 years – the snowboard. A white board, which is about 1-foot by 1-foot, is set in the snow outside the Chanhassen office. Another one is set several hundred feet away and a third sits at Minneapolis-St. Paul Airport.
"What we want to do is have a white board so it reflects the sunlight and allows the snow to stay on the board and not melt," says Michelle Margraf, a meteorologist at the NWS Office in Chanhassen.
Every six hours, a meteorologist will stick a ruler into four or five places in the snow that's fallen on the board. They'll take the average of those measurements and then wipe the board clean. A long, orange pole lets the meteorologists where to find the board.
One of their biggest challenges, though, is dealing with the wind that can push around the snow, so they have other back-up ways to measure. The NWS meteorologists can measure the snow depth at three different places and see how it's changed in the last six hours. They also use the rain gauge to collect snow and then bring it inside to melt before measuring the water. That also has the benefit of giving them the water content of the snow.
Margraf says precise estimates of snowfall are important to have accurate flood forecasts. Historical snow averages can also help cities and counties determine the amounts of equipment they'll need for snow removal each year.
And, as for why you might get a higher measurement at home?
"That's the interesting thing," Margraf said. "If you go in the backyard with your stick, usually you have grass below and it can add a couple of inches to your measurement depending how short your grass was."