Rain gauge replaced — but how will record be corrected?
After much scrutiny over accuracy of data, new device installed at San Jose's airport
San Jose is overhauling its suspect rain measurement system — but the mystery around the data it's been collecting hasn't evaporated just yet.
Officials at the National Weather Service said March 16 they replaced a rain gauge at San Jose Mineta International Airport — the source of the city's official precipitation data — that previously had been reporting what were believed to be grossly inaccurate numbers. The swap came after intense public criticism of the meager totals in a historically rainy year, the agency said, even though a fourth inspection of the device this year showed nothing wrong with the existing weather instrument.
“It was kind of like, so many questions have arisen, why not just put in a brandnew rain gauge?” said Warren Blier, the weather service's science and operations officer.
The data is considered by weather amateurs and officials alike to be hugely important for the scientific community, policymakers and historical record keeping.
Joseph Gemignani, an amateur weatherman who has been following the San Jose rain gauge debacle, said he is glad the device has been replaced. But he questions why such an important measuring tool is located at the airport, plopped in between the runways.
“It should be somewhere more geographically centered — not out in the boondocks,” he said.
What will end up being written down in the weather history books is still murky, officials said. The airport data currently stands at 12.59 inches as of March 16, well below a nearby gauge that is reporting just above 19. In a weather season that is now rivaling the El Niño storms that ripped across California between 1997 and 1998, weather experts say a correction to the data is critical. But how?
According to Cynthia Palmer, meteorologist in charge at the National Weather Service in Monterey, other rain gauges in San Jose that aren't overseen by their agency likely won't be used to correct the record, due to concern that those devices aren't offering the most accurate data either or aren't always calibrated. That includes the Santa Clara Valley Water District's rain gauge at San Jose's Civic Center, located 1.3 miles south of the airport and currently reporting a whopping 6.5 inches more than the weather service.
That leaves a few possibilities to help fix the record. They include a smattering of other weather service sites around the Bay Area that collect rain data, as well as the gauge at Moffett Field in Mountain View, which was handed over by the weather service to NASA but may be used to average the numbers out, the agency said. The decision will ultimately be made by the National Centers for Environmental Information, an arm of the National Oceanic and Atmospheric Administration.
According to Jan Null, a longtime former National Weather Service official and owner of the online website Golden Gate Weather Services, there is precedent for using non-national Weather Service gauges to correct the record.
A malfunctioning gauge overseen by the weather service in San Francisco had its data from 1973 to 1982 replaced with numbers from a device controlled by a nearby television station. The faulty rain gauge was located at the Federal Building on 50 Fulton St., while the television station's device was 500 feet north at 277 Golden Gate Ave.
So far, there are signs that the replacement gauge at the airport may have done the trick. While the airport and water district gauges had begun diverging starting in October, a comparison of March data shows the rain tallies are now closely aligned.
“It's important data,” said Null, referring to the San Jose airport situation. “And it needs to be constructed in the best scientific manner possible.”