Weather Watch

How much more rain can SLO County expect this winter? The ‘storm door’ is wide open

Ranchers love the November rains as they promote an early start to the grasses that will transform our hills to emerald green over the next few weeks. That certainly wasn’t case during the first part of November.

Firmly anchored off the California coastline, the Eastern Pacific High and transitory high-pressure systems at the surface moved over the Great Basin — the area between the Sierra Nevada range to the west and the Rocky Mountains to the east. This condition created persistent Santa Lucia northeasterly (offshore) winds that brought warm and bone-dry weather.

Then a significant change occurred in the latter part of November; the Eastern Pacific High shifted north into the eastern Gulf of Alaska while the southern branch of the polar jet moved southward carving out low-pressure systems and transporting these storms across the ocean toward California.

In other words, the storm door is opened.

Despite the arid conditions during the first half of November, locations throughout the Central Coast have recorded above average rainfall for the month. Paso Robles receives typically about an inch of rain in November, but this past month it recorded 2.34 inches. Cal Poly, which has rainfall records stretching back nearly 150 years, reported 4.18 inches this November, nearly double the typical November. The Santa Maria Airport has reported about an inch and a half of precious rain, or about 112 percent of normal. For the rain season, is reporting 140 percent of average.

The U.S. Monthly Drought Outlook indicates that the drought classifications in Northern and the northern half of Central California will likely be removed by the end of the year. Areas south of Paso Robles into Santa Barbara County will see drought classifications continue, but will they probably improve.

So what caused this dramatic change in the weather pattern?

Nobody knows for sure, but it may have been caused by El Niño (warmer than normal sea surface temperatures in eastern Equatorial Pacific).

These warmer waters in the eastern Pacific produce a more considerable amount of evaporation. As this water vapor ascends into the atmosphere, it often condenses into thunderstorms and releases tremendous amounts of latent heat, which further decreases the atmospheric pressure. This area of low pressure, in turn, changes the path of the southern branch of the polar jet stream, pulling it farther southward toward the Central Coast.

The Climate Prediction Center is advertising that “El Niño is favored to form this winter with an 80 percent chance.”

More importantly, the strength of this expected El Niño event should have a bearing on the amount of rainfall the Central Coast will receive. Typically, in San Luis Obispo and Santa Barbara counties, the higher the classification of the El Niño event, the more rain it will create.

Neutral El Niño conditions — or El Nada or weak El Niño — typically don’t produce any reliable seasonal rainfall predictions along the Central Coast, but a moderate, strong or very strong more times than not do.

Over the past month, the numerical models have increased the predicted El Niño category to a moderate strength level for this winter.

This condition typically produces about 110 percent of above-average rainfall in San Luis Obispo County and normal rainfall amounts in Santa Barbara County.

With that said, here are my rain season’s predicted rainfall totals: Cambria, 24 inches; Paso Robles, 14; San Luis Obispo, 25; Nipomo, 20; Santa Maria, 14; Lompoc, 16; and Santa Ynez, 20.

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Not only will these storms produce much-needed rain, but also high sea and swell events. At PG&E, the safety of customers and employees is a top priority. If you ventured to the coastline to observe these waves, please remember not to climb rock walls or jetties, keep children and pets back from the water’s edge and never turn your back to the ocean.

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 or follow him on Twitter: @PGE_John.
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