Weather Watch

The October rain was nice. But here’s why it’ll be an Indian summer rather than a wet fall

A well-advertised low-pressure system swept through the Central Coast on Wednesday with much-needed rain, the first in over six months. Most locations throughout San Luis Obispo and Santa Barbara counties recorded between a quarter and nine-tenths of an inch of precious rain.

I was hoping this would start a trend for the rest of October, and here is why.

Civil engineer John Neil is the manager of the Atascadero Mutual Water Company. Neil loves the science of hydrology and meteorology and their potential impact on people’s lives. The company has collected rainfall data since 1914 at a gauge at the confluence of the Salinas River and Atascadero Creek.

After he reviewed the historical data from this rain gauge, Neil discovered that when the area received more than 2 inches of precipitation during October, the rest of the rain season — which runs through June 30 of the following year — was higher than average. Neil calls this the “2-inches-of-rain-in-October rule.”

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Cynthia Rios walks along Marsh Street at Chorro on Wednesday. The first rain in months brought puddles and umbrellas to the streets of San Luis Obispo County. David Middlecamp dmiddlecamp@thetribunenews.com

Unfortunately, their rain gauge may not reach 2 inches this October as it’s looking mostly dry with above-normal temperatures through the end of the month and perhaps into the first week of November. Of course, that doesn’t necessarily mean a below-average rainfall year, which runs from July 1 through June 30.

What it does mean, however, is that summer-like weather may return to the Central Coast.

Many local folks referred to this as our “Indian summer,” which from a meteorological standpoint refers to a period of above-normal temperatures after a spell of unsettled weather during autumn.

As so often occurs during this season, an area of high pressure will build at the surface over the Great Basin and will produce Santa Lucia (northeasterly/offshore) winds, especially during the night and morning hours.

There has been much research on where the term “Indian summer” originated.

While no one knows for sure, it may have been first recorded in the late 1700s by a New England farmer named J. H. St. John de Crèvecoeur, who wrote in a letter, “Then a severe frost succeeds which prepares it to receive the voluminous coat of snow which is soon to follow; though it is often preceded by a short interval of smoke and mildness, called the Indian Summer.”

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The phrase may have come from the fact that many Native American tribes deliberately set fires to promote a diversity of habitats. Along the Central Coast, Bishop pine groves thrive on periodic burns as they need heat for the pine cone seeds to germinate. The burning was useful to divert deer and other big game into small, unburned areas for easier hunting.

As the days became shorter during the fall, Native Americans discovered that deer, especially bucks, were preoccupied with the rut and less cautious than usual.

The early European settlers in the country, witnessing the smoke and hazy conditions along with the more considerable amount of hunting activity by the tribes during autumn, probably associated this weather phenomenon with “Indians.”

The common reference to the term “Indian summer” over the years has increased. It’s been estimated that air temperatures have increased several degrees Fahrenheit since the late 1700s, hence, the warmer Octobers and Novembers and the greater use of the term.

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A warming climate combined with an increasing numbers of extreme weather events are causing unprecedented and unanticipated wildfires. Launched in late March, the PG&E’s Community Wildfire Safety Program has developed and implemented additional precautionary measures intended to reduce wildfire threats and strengthen communities for the future. These new safety measures are more critical than ever given the dramatically increasing and devastating wildfires the state has experienced during both the 2017 and 2018 wildfire seasons. To learn more, visit pge.com.

John Lindsey’s column is special to The Tribune. He is PG&E’s Diablo Canyon marine meteorologist and a media relations representative. Email him at pgeweather@pge.com or follow him on Twitter: @PGE_John.
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