What will happen to vital San Jose rain data?

The mystery around San Jose airport’s rain data hasn’t evaporated just yet.

Officials at the National Weather Service said Thursday that they replaced a rain gauge at San Jose Mineta International Airport which had been previously reporting what was believed to be grossly inaccurate numbers. The swap came after intense public scrutiny of the data, the agency said, and a fourth inspection of the device this year which yet again showed nothing was suspect with the existing weather instrument.

“It was kind of like, so many questions have arisen, why not just put in a brand new rain gauge?” said NWS’s Science and Operations Officer Warren Blier.

The data is considered by many weather amateurs and experts alike to be hugely important for the scientific community, policymakers and historical recordkeeping.

But 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. And 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 vitally important.

According to Meteorologist-in-Charge Cynthia Palmer, 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 or aren’t always calibrated. That includes the Santa Clara Valley Water District’s rain gauge at San Jose’s Civic Center, located just 1.3 miles south of the airport and currently reporting a whopping 6.5-inch difference.

That leaves a few possibilities to help fix the record. They include a smattering of climate sites around San Jose that collect rain data, as well as the gauge at Moffett Field in Mountain View, which was handed over by NWS to the National Aeronautics and Space Administration but may be used to average the numbers out, the agency said. The decision will be ultimately be made by the National Centers for Environmental Information, an arm of the National Oceanic and Atmospheric Administration.

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According to Jan Null, a longtime former NWS official and the owner of the online website Golden Gate Weather Services, there is precedent for using non-NWS gauges to correct the record.

A malfunctioning gauge overseen by NWS 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’s 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.”

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