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Community Corner

As Region Cools, Gilroy Simmers: Weather Expert Explains

Andrew Van Tuyl, an online Meteorology Professor at Gavilan College, tells why Gilroy is so hot.

Anyone to sweat out the summer in the Garlic City experienced average high temperatures of 85 degrees, and 100 degrees on the most stifling days. 

Even as the summer heat waves melt into more forgiving conditions in surrounding cities, the relentless Gilroy sun beats down.

Thus far, September in Gilroy has seen temperatures in the high 70s and low 80s. San Jose and Watsonville, for example, prep for autumn with general temperatures 10 to 20 degrees lower than those of Gilroy. Why is Gilroy so sweltering compared with the rest of Santa Clara County?

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Gilroy is hotter than most of Santa Clara county because of its particular topography and location relative to the Pacific Ocean, according to Andrew Van Tuyl, an online Meteorology Professor at Gavilan College.

Throughout the summer months, said Van Tuyl, the ground heats up rapidly, while the ocean remains cold to the west. This causes temperature to increase the farther you are from the ocean.

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“Gilroy is part of a valley, which is open on the northwestern end towards San Jose and the San Francisco Bay Area, which are open to the ocean air, so you end up with cooler weather up there,” said Van Tuyl.

Van Tuyl has practiced meteorology for over 35 years. He received his undergraduate degree in 1970 from Pennsylvania State University focusing on meteorology, and has taught a Meteorological Society course since 2006.  

According to Van Tuyl, Gilroy’s surrounding mountains stand like guards to prevent much of the cool ocean air from entering the city. The placement of the Santa Cruz Mountains to the west, and the Diablo Mountain Range to the east creates a barricade to cold ocean air, as well as clouds, that would otherwise drift in from the Monterey Bay. This is because cool air is denser than warm air, so warm air passes more easily through the mountains, while cool air tends to flow down valleys before reaching Gilroy.  

Any air flowing down the mountains into the city is also warmed by compression, although Van Tuyl says this is probably a small effect of the mountains near Gilroy, as it is a more noticeable trait when dealing with taller mountain ranges.   

Wind patterns also impact the region’s climate, Van Tuyl explained. Gilroy, the southernmost city in Santa Clara County, lies at the southeastern end of the vast Santa Clara valley.

“Prevailing winds during summer are mostly from the west or northwest, or generally down the valley,” said Van Tuyl in an email. “The valley is open toward the bay at its northwestern end, so that portion of the county gets more influence from the ocean air. Gilroy, being farther from the bay, is not cooled as much.”

All in all, wind, topography and location combine to roast Gilroy late into the summer, and Van Tuyl said climate change forebodes even more parching patterns in years to come.

“California has been warming for the last 30 years,” he said. “In general the state has been warming about 1 degree Fahrenheit since 1980 every year.”

So stock up on sunscreen, conserve your water and energy, because it’s probable that more than garlic will keep sizzling in Gilroy.

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