Does a wet October mean more rainfall? Here’s what one SLO County weather watcher thinks

This October, Santa Maria was much wetter than average.

Santa Maria was also cooler, with a mean temperature of 60.1 degrees Fahrenheit, which was 2.1 degrees below normal.

According to Climate Central, the Central Coast city received 1.29 inches of precipitation that month — 239% of the typical amount of rain.

Despite this month being cooler than usual, Octobers in Santa Maria are getting hotter, leading to a change of 4.5 degrees Fahrenheit since 1970.

October is also the month with the fastest rate of warming in Santa Maria.

San Luis Obispo County Regional Airport recorded 1.70 inches of rain this October. Typically, the airport only sees 0.70 of an inch of precipitation.

The average temperature this October was 63 degrees or about one-half of a degree below normal.

The Paso Robles Municipal Airport recorded 1.57 inches of rain, or, 280% of average rainfall in October. Much like San Luis Obispo, Paso Robles was also about one-half of a degree cooler than typical.

This leads to the question: Will the rest of the year see above-normal rainfall?

In summer, the Climate Prediction Center issued a watch for La Niña in the heart of our upcoming rainfall season, November 2021 through March 2022.

Their forecast verified and La Niña conditions have developed with Equatorial Sea surface temperatures (SSTs) below average across the central and east-central Pacific Ocean.

La Niña is expected to continue through February 2022.

So, what is La Niña? It is mostly ocean temperatures and the way the atmosphere responds to them.

Overall, moderate or strong La Niña conditions typically produce lower-than-average winter rainfall. However, there have been a few La Niña years that have produced well above average rainfall amounts.

So how do these above or below average seawater temperatures in an area so far away have such a profound effect upon California’s weather?

The answer is in the winds, or, should I say, the upper-level winds.

La Niña tends to drive the storm track (upper-level winds) further northward into the Pacific Northwest, leaving the Central Coast with fewer storms.

In fact, over the past 60 years, La Niña has typically produced about 86% of average rainfall for the Central Coast.

Another method is to look at historical rainfall data. Sometimes, the answer to the formidable rainfall question is right under our noses. Let me explain.

The Atascadero Mutual Water Company was incorporated in 1913 by Atascadero’s founder, E.G., Lewis, and meets the water requirements of more than 30,000 people.

Since 1914, the company has collected rainfall information at a rain gauge at the confluence of the Salinas River and Atascadero Creek, forming a database that contains more than a century of rainfall statistics and well-water levels.

Civil engineer John Neil is the manager of the Atascadero Mutual Water Company (AMWC) and is very active in the Atascadero Rotary Club.

Neil loves the science of hydrology and meteorology and their potential impact on people’s lives.

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

In other words, since 1914, the months that follow a wet October over the course of the rain season have experienced above-average rainfall.

Neil calls this the “two inches of rain in October” rule.

However, in years they record measurable rain in July, less-than-average precipitation for the season follows despite what occurs in October.

Unfortunately, Atascadero had quantifiable rain in July.

However, John did record 2.01 inches of rain at the Atascadero Mutual Water Company this October.

Here are AMWC’s rainfall data for October sorted from highest October rainfall to lowest compared to the annual total. The rain year ends June 30, and the average season total for these 10 years is 17.26 inches.

“It’ll be interesting to see if the ‘two inches of rain in October’ hypothesis holds true this year,” John told me.

I’ve been forecasting weather along the Central Coast since 1991, and my confidence in John Neil, the oracle from Atascadero, has grown considerably over the years.

Santa Maria fundraiser

The Santa Maria Museum of Flight is hosting a veteran’s charity fundraiser on Saturday, Nov. 13, over Veterans Day weekend at the Santa Maria Public Airport.

The 30th Anniversary Rocketeer charity event includes tours of the museum, a prime rib dinner,

drinks and a screening of “The Rocketeer” in the hanger where some of the movie was filmed. Proceeds from the event will go towards four local nonprofit charities: Santa Maria Museum of Flight, Central Coast Film Society, Band of Brothers and the Civil Air Patrol.