PROVIDENCE — Key snowfall amounts for a possibly historic winter storm this weekend will come from regular folks living in cities big and small across New England.
They are members of the Community Collaborative Rain, Hail and Snow Network (CoCoRaHS), a nonprofit, community-based network of volunteers of all ages and backgroundswho measure and map rain, hail, and snow. There are hundreds of members across New England and all they use is a low-cost gauge that meets National Weather Service Standards.
“There was a flood event that happened in 1997,” CoCoRaHS Education and Outreach Coordinator Noah Newman told The Globe. “Basically at the time, the one rain gauge was at the airport. But on the west side of town, they got close to 14 inches. That was a known problem. We all know it can rain across the street in different amounts.”
As scientists from CSU were kicking on doors doing bucket surveys to find out how much rain fell, people started offering to set up their own rain gauges and let them know how much rain they got.
“It was a ‘Eureka’ moment, good timing, and it really just took off,” Newman said. “Now we have loyal observers some who have been with us since their state joined the network.”
The group was founded by now-retired, but still active Colorado state climatologist Nolan Doeskin, who organized everyone under an umbrella called CoCoRaHS. They are now the largest source of precipitation data for the National Weather Service.
Each member takes manual measurements and does not use automated gauges. They are equipped to measure snowfall. They purchase the approved gauges on the CoCoRaHS website for about $30.
“You have to empty it and set it back up for the next day,” Newman said.
But now they are located in all 50 states, Canada, Puerto Rico, and the Bahamas.
CoCoRaHS’s focus is on training and education and its observations are public. It first popped up at Colorado State University in Fort Collins, Colorado, in 1997, as a small group of citizen scientists.
“These volunteers are filling in the gaps. It’s extremely important to the NWS,” Newman said. “Researchers from universities, farmers, agriculturists, insurance industries use the data. It’s free for anyone and useful in multiple applications.”
NWS science and operations officer Joe Dellicarpini said the NWS relies on data they collect from the public because it fills in gaps in reports like the ones they get from their official stations. The manual measurements give them information that automated gauges could underreport.
That data can be used for drought or flood assessments provided to states.
“The more data we have from the observers the more detail we can give to the state as far as drought management,” Dellicarpini said.
Matthew Belk, a meteorologist for the National Weather Service in Boston, said he couldn’t speak on behalf of the entire NWS, but the Boston station relies on any information they can get from the public during or after weather events. He said the NWS is a public domain that works with pretty much anybody who can provide “trusted” information.
Newman said they can never have enough volunteers, especially in rural areas where there is less data.
There are more than 400 volunteers in the active CoCoRaHS network spread across New England.
Just yesterday, Newman said he sent out emails to 2,000 volunteers up and down the Eastern Seaboard in preparation for this weekend’s winter storm. He provided them with last-minute tips and instructions on how to take measurements.
“The rain gauge comes built-in with an intertube for measuring rain,” he said. “You have to remove it to measure snow.”
Not everyone reports winter precipitation totals to CoCoRaHS with a gauge. Some stick with a ruler and report how deep the snow is.
But the most valuable data is the water content in snow.
“When observers submit that data we provide to them afterward with their ratio,” Newman said. “You might have a ratio of 15 to 20 inches of snow to an inch of rain if it’s light fluffy snow. Those numbers are extra meaningful to the NWS.”
The most commonly known ratio of rain to snow is 10 inches for every inch of rain. However, the conversion is only for temperatures 27 to 34 degrees. The colder the temperature, the lighter and more robust the snowfall totals. A storm on a 10 to 12 degree day could produce 30 inches of snow for every inch of rain.
An online calculator by OmniCalculator can help you determine the water to snow ratio.