Weather Watch

Cal Poly's weather station plays a key role in county history

Special to The TribuneMarch 1, 2014 

Martha Moak and Hilary Olsen are the keepers of the official Cal Poly rain gauge.


Most of us are separated by just a few generations from our agrarian past.

My grandfather, Tom Lindsey, raised crops in Covington, Tennessee, while my mother’s side of the family farmed in Colusa County in Northern California. Farmers and ranchers who labor to raise our food have always known the importance of water.

If there’s a silver lining to our drought, it’s clearly showed the reliance we all have on winter rains like we have been experiencing in the last few days. Accurate, long-term rainfall data is key to making educated decisions about climate and water resources.

The home of climatology for San Luis Obispo is Cal Poly. We are blessed to have one of the longest records of climatology in the state of California, stretching back nearly 150 years.

But if Cal Poly wasn’t established until 1901, where did the early data come from?

John Slayton of Azusa, Calif. has researched the history of weather stations throughout the west. According to Slayton, frontier doctor W.W. Hayes moved to San Luis Obispo in 1866 and kept daily temperature and rainfall records that he sent to the Smithsonian Institution.

At the time, Joseph Henry, Secretary of the Smithsonian Institution in Washington D.C., envisioned that storms could be predicted by telegraphing ahead what was on the way.

In 1885, the U.S. Army Signal Corps, the forerunner of the National Weather Service, installed the weather station on top of the Andrews Hotel in downtown San Luis Obispo. When the hotel burnt down, the weather station was moved to various downtown locations including the Andrews bank building, from 1894 through 1927. In 1927 the station was moved to Cal Poly.

For many years the Cal Poly Police Department recorded weather data, mostly because the officers were on duty around the clock. If the temperature fell below freezing in the middle of the night, they contacted the Crop Science Department, which would take steps to protect sensitive plants from frost.

In the recent past, Kim Busby-Porter, water quality management specialist with Cal Poly, reported the rain. Today, the keeper of the official rain gauge is Hilary Olsen and Martha Moak, Irrigation Training and Research Center (ITRC) student employees with guidance by Dr. Stuart Styles.

These bright and dedicated women showed me many types of rain gauges stationed at the ITRC official weather station.

Their standard rain gauge, a type used for more than a century, consists of a large metal cylinder (20 inches high and 8 inches in diameter) with a funnel on top. It drains rain into a narrow tube that has one-tenth the cross sectional area of the cylinder. Hence, the amount of rain is exaggerated by a factor of 10, producing precise rainfall measurements.

A calibrated fiberglass scale is put into the tube and withdrawn. The wet portion of the scale indicates the water depth and amount of rain to one-hundredth of an inch. If more than 2 inches of rain have fallen, the excess water is caught in the outer shell of the cylinder and can be measured later.

Another type of rain gauge utilizes a tipping bucket. It funnels rain into a very small bucket, and when the equivalent of one-hundredth of an inch of rain accumulates, the bucket tips over and drains the water while at the same time activating an electronic switch that records and reports rainfall. The problem with a tipping bucket is during downpours you can lose a small amount of precipitation during each bucket tip, thereby slightly underreporting total rainfall.

The official rain gauge on campus is a weighing type. This gauge captures the rain in a fixed bucket that sits on a sensitive weight scale. The scale translates the accumulated weight of the rain into readings of a hundredth of an inch. The precipitation totals are recorded on an SD card and the data is uploaded to a computer. Once a month, the data is downloaded and sent to the NWS.

Their observations are officially archived and certified by the National Climate Data Center (NCDC). NCDC was designated by the Federal Records Act of 1950 as the official United States archive for climate data records.

Weather data from this station can be viewed at

In late January, Ernest Righetti who lived his entire life in Edna Valley passed away. He was an anchor and visionary in the counties’ agricultural community. Everyone who knew him called him Ernie. In 1967 he was the first farmer to raise avocados in our area. He certainly knew the importance of accurate measurement of meteorological data.

Ernie and his sons were and are ardent supporters of the Cal Poly weather station. To keep this vital service going, Ernest Righetti’s family suggests donations be sent for the support and maintenance of the Cal Poly official weather station. To learn more, please visit:

John Lindsey’s column is special to The Tribune. He is a media relations representative for PG&E and a longtime local meteorologist. He is president of the Point San Luis Lighthouse Keepers. If you have a question, send him an email at

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