National Weather Service seeks volunteers to be the "eye" of the storm
November 12, 2009
The saying goes: If you don’t like the weather in Colorado, just wait a minute.
Colorado’s weather is as rapidly changing as it is unpredictable. National Weather Service senior forecaster Chad Gimmestad has made a career trying to decipher how the bumpy terrain in the northern part of the state affects the movement of weather systems.
“There’s still a lot we don’t know,” he said.
Granby, for example, presents an enigma to forecasters due to a lack of historical climate data. When an early season snowstorm struck Colorado just before Halloween, the Weather Service could look down at Granby via satellite and see thick snow clouds, but they had no way of knowing what was happening on the ground.
“It’s a big challenge for us to say when it’s going to snow hard in the valley there,” Gimmestad said.
The best way to improve the weather service’s understanding of how the landscape plays with Colorado’s storm systems is to gather as much data as possible during weather events, Gimmestad said.
The Weather Service wants you
To do that, the NWS is recruiting volunteers to help gather data and to be the “eye” of the storm.
The CoCoRaHS program is a community collaborative started in 1998 after a flash flood in Fort Collins. At that time, it was discovered that the city’s two official weather stations only picked up several inches of rain while a few miles away there was more than a foot of rain in the same time period.
“We realized that we were not observing those kinds of event on the scale that we need to be,” Gimmestad said. “The official climate record still says that there were only a few inches of rain in Fort Collins that day.”
Because official weather stations are scattered around the country, “an 8-inch diameter bucket represents the weather for a 50-mile area,” Gimmestad said. “For some things that’s OK. It gives us a large-scale, general picture. But a lot of events are being missed, especially in places where precipitation changes a lot over a short distance.”
Grand County residents know that on any given day the weather in Kremmling can be vastly different than the weather in Fraser. One weather report could almost never do justice to the entire region.
“The scale of the mountains can change the weather within one or two miles,” Gimmestad said. “People up there in Grand County who are paying attention will notice that. They will realize that there is always more snow on one side of a hill than the other.”
When a CoCoRaHS volunteer started taking measurements northwest of Kremmling, NWS forecasters learned right away that “it snows more there than we thought,” Gimmestad. “Snow blows over the ridge and accumulates. After that, we got more careful with assuming it would be dry everywhere in Kremmling.”
Granby also tends to be drier than the surrounding areas.
“We can see a donut hole over Granby, but we don’t understand exactly why that is happening. The mountains play some role, but they don’t form a perfect circle around Granby.”
The CoCoRaHS program puts volunteers in charge of measuring rain, hail and snow in their backyards and entering the data of the NWS map. The site is constantly updated, and measurements can be real time, Gimmestad said. The information is also archived and available to the public for anyone who wants to do weather research.
There are currently only a handful of people in Grand County participating regularly in the program, and there are some big gaps in the data, Gimmestad said.
“We have a cluster of people around Kremmling, Grand Lake and scattered in the Fraser Valley. But, even when you have several volunteers they are not always there on same day.”
It’s definitely a case of the more the merrier, Gimmestad said: “One of the purposes of project is to study how much variability there is in small distance, even between neighbors. Over time, we can see what the pattern is.”
The National Weather Service maintains official stations in Winter Park, Fraser, 6 miles south-southwest of Grand Lake (at the NPS facility), 1 mile northwest of Grand Lake (at the RMNP
visitor center), Green Mountain Dam, and Kremmling. Each of those stations has historical data that goes back decades., Gimmestad said. But, there is no estimate as to how much drier Granby is than the surrounding areas. Hot Sulphur also has a dearth of data.
CoCoRaHS volunteers are required to purchase a 4-inch diameter rain gauge, available through several vendors on the NWS Web site for $25. To measure snow, volunteers set up a flat protected surface such as a piece of plywood.
Having access to a computer and the Internet is key to participating in CoCoRaHS. Volunteers sign up online and enter data directly into the Web site. The online map is updated in real-time as volunteers enter data. Training is free at http://www.cocorahs.org.
For those who aren’t interested in measuring precipitation, there is also a need for weather spotters who provide observational data. Weather spotters let the NWS know when forecasts are way off base or right on the money, and they report instances of heavy snow, hail and damaging wind.
This information helps the weather service improve its ability to make accurate forecasts in the future, Gimmestad said.
Weather spotters are given a toll free number to call, and they are connected directly to somebody at the weather center in Boulder. In turn, weather forecasters will occasionally call a weather spotter to ask what the weather is doing when they can’t tell from the satellite.
The weather service aims to build forecasts on a 3-mile grid at its Web site http://www.weather.gov.
“We are still learning and trying to serve every spot on the map,” Gimmestad said. “Getting people to call in helps us. It also helps your neighbors. By letting us know its snowing hard in Hot Sulphur, we can give that information to people who live in Granby that are going that way.”
– Reid Armstrong can be reached at 970-887-3334 ext. 19610 or firstname.lastname@example.org.