Weather Watch

Fall is here, and I’m thinking about rain on the Central Coast. Or will it be drought?

The arrival of the autumnal equinox — the beginning of fall — will occur at 1:50 a.m. Monday when the sun will be directly over the equator. We will lose the highest amount of daylight of the year on Monday, about three minutes at our latitude.

The Earth will move closer to the sun as we head toward winter because our orbit is not perfectly round, but slightly oval-shaped. Earth will reach perihelion, when the whole planet comes closest to the sun on Jan. 4, 2020, around midnight local time.

Aphelion, when Earth is farthest from the sun, will happen July 4, 2020, or about a 3 million-mile difference between perihelion and aphelion. This condition helps to make the northern hemisphere’s winters and summers kinder versus the southern hemisphere.

Not only is the autumnal equinox near the peak of the hurricane season, but the equatorial regions are now absorbing much more of the sun’s energy as the Arctic Circle moves toward the winter solstice and perpetual darkness on Dec. 21, the longest night of the year.

Nature never likes anything out of balance, and soon massive mid-latitude cyclones, many times larger in size than hurricanes, will begin to develop in the vast expanse of the North Pacific to attempt to equalize the atmospheric temperature differentials between the equatorial belt and the northern latitudes.

As these mid-latitude Pacific storms develop, will the upper-level (jet steam) westerly winds primarily travel at a direct path across the Pacific and bring rain to California or will these winds shift further northward and carry these tempests into the Pacific Northwest? The answer to this question will help to determine if it will be a dry or wet year.

Depending on the strength of these low-pressure systems, historically, a dry year will experience between one and four storms, while a wet year will encounter between five and nine — or even more significant rainfall events. However, just one big atmospheric river (AR) event can alter that statement.

According to the Climate Prediction Center, the infamous neutral condition — “El Nothing” or “El Nada” — will continue into winter.

NOAA uses Niño 3.4, an area of sea-surface temperatures (SST) in a central equatorial region of the Pacific Ocean, as the standard for classifying El Niño (warmer-than-normal SST) and La Niña (cooler-than-normal SST) events.

The classification of the El Niño-Southern Oscillation (ENSO), or El Niño, La Niña or neutral conditions, historically has had a bearing on the amount of rainfall California will receive.

Typically, the higher the classification of the El Niño event, the more rain it will create. On the other hand, La Niña events tend to produce less precipitation as the upper-level winds shift farther northward. Unfortunately, the neutral condition combined with another large-scale ocean water temperature cycle may produce lower-than-average winter rainfall this year.

The other large-scale ocean water temperature cycle is the Pacific Decadal Oscillation (PDO), which can increase or decrease the ENSO effect. The PDO is found primarily in the North Pacific. The phases of the PDO are called warm phases or cool phases. Unlike ENSO, which focuses on the sea-surface temperature in the central equatorial region of the Pacific, the PDO is classified by seawater temperatures throughout the northern Pacific Ocean.

The models are indicating that it will continue to shift to the cool phase, which means a higher chance of below-normal rainfall.

Another wildcard is the marine heatwave or “The Blob” that is currently stretched across much of the northern Pacific. So far, seawater temperatures at the ocean’s surface are as much as 6 degrees warmer than usual. Along the immediate coastline of Central California, seawater temperatures are running slightly below normal due to higher amounts of upwelling; however, the Northern California coastline is experiencing above normal seawater temperatures.

Some scientist hypothesized that “The Blob Part One,” which started in 2014 may have contributed to one of the worst droughts in California’s history. What these warmer than average seawater temperatures will do is increase the amount of water vapor the atmosphere can hold and the chance of more intense ARs if they develop.

These rivers in the sky can stretch for thousands of miles across the world’s oceans, but they are only a few hundred miles wide. They can draw vast amounts of water vapor into narrow bands ahead of cold fronts and transport ridiculous amounts of water across vast expanses.

In fact, they can carry more fresh water than the Amazon River. Along the West Coast, they are informally called the “Pineapple Express.” The Pineapple Express is a subset of an atmospheric river event that originates in the tropical waters near Hawaii, hence the pineapples. In the past, meteorologists simply referred to these as “the hose.”

With that said, the predictions of ENSO conditions are often wrong.

However, if the current models verify, we could see lower than average amounts for rainfall in California this winter, but only time will tell the story.

Guess the first day of rain

I will be on the Dave Congalton Show on KVEC Radio from 4 to 5 p.m. Tuesday for the “Guess the First Day of Rain Contest.” Call 805-543-8830 during the show and predict the first day the Central Coast will receive at least 1 inch of rain over a 24-hour period at any calibrated rain gauge in the region, such as Cal Poly, the Santa Maria or San Luis Obispo airports — or even Rocky Butte. The winner will receive a PG&E umbrella, flashlight and safety kit that can be used during storms.

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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