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Since You Asked: There’s a cloudburst behind rainfall data

The Mail Tribune’s rain totals for the first four days of July, as reported in the paper, totaled 0.03 inches, but my rain gauge measured exactly 1 inch during that time. I live in east Medford. Where does the Mail Tribune collect its rainfall data?

— Bernard H., via email

You asked a question that unfolds like an umbrella, Bernard, with many potential parts, but we’ll focus on the vital points. First, our rainfall data comes from Accuweather, an international forecasting company founded in 1962 by a meteorology student in Pennsylvania.

Where does Accuweather get its data for the Rogue Valley?

Accuweather customer service representative Daniel Vann said the company uses an instrument at the Medford airport called an ASOS station to record precipitation for our region.

Why would a rain gauge in east Medford get a dramatically different reading than a weather station at the airport?

“There are many factors that might contribute to different observations,” said E. Jamie Trammell, associate professor and chair of Southern Oregon University’s Environmental Science, Policy & Sustainability program.

“The biggest factor to consider, in the case of precipitation, is the type and quality of the instrument and how often it has been calibrated. For example, a simple rain gauge isn’t as accurate as a tipping bucket that has been calibrated to (National Institute of Standards and Technology) specs,” he said.

There also are variations in weather — Trammell called them microclimates — throughout the Rogue Valley.

So it seems likely that it just rained harder in east Medford during the first week of July than it did at the airport, Bernard.

Send questions to “Since You Asked,” Mail Tribune Newsroom, P.O. Box 1108, Medford, OR 97501; or by email to youasked@rosebudmedia.com.