Central Coast rain

The setting sun gilds the edge of storm clouds even as wisps of rain stream down toward the Pacific Ocean off the Central Coast. Forecast models are calling for the weather to get wetter in March, but only time will tell.

Over the past few weeks, long-range weather models have advertised a stormy and wet weather pattern for March with little variance in their output.

Of course, they are long-range models, and they could certainly change; however, confidence continues to build that they will verify.

A few of the U.S. Navy Fleet Numerical Meteorology and Oceanography Center model runs hint of an atmospheric river developing by the first week of March.

The term “atmospheric river” hasn’t been around very long. None of my oceanographic and atmospheric textbooks show any reference to it.

Turns out, the phrase was coined by researchers Reginald Newell and Yong Zhu of the Massachusetts Institute of Technology in the early 1990s.

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 huge amounts of water vapor into narrow bands ahead of cold fronts and transport fantastic amounts of that liquid 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 “pineapple” reference. In the past, meteorologists simply referred to theM as “the hose.”

They can certainly increase rainfall totals along the Central Coast. Historically, March in northern Santa Barbara County can be wet — averaging about 3.2 inches of rain at the Santa Maria Public Airport.

Back in March 1995, a storm developed about 900 miles off the Central Coast and caused an intense cold front to stall over our area that tapped into a plume of subtropical moisture stretching back to Hawaii.

The rain began to fall early on March 9 and continued through the next day, producing amazing 24-hour rainfall totals. The Diablo Canyon Power Plant recorded 8.5 inches of rain in just 24 hours.

The stalled cold front was accompanied by gale- to storm-force 55- to 73-mph southeasterly winds in the coastal regions. San Simeon reported sustained wind speeds of 70 mph, with gusts reaching 88 mph.

The winds produced a great amount of orographic enhancement. As the air mass is lifted up over our coastal mountains, it rises into lower-pressure air, cools and eventually reaches its dew-point temperature.

When that occurs, rain will develop on the windward side of the mountain. Like squeezing a wet sponge, moisture from the air mass is released in the form of precipitation.

Up in San Luis Obispo County, some locations in the hills above Cambria and along the Cuesta Grade reported rainfall amounts exceeding 12 inches over 24 hours.

Numerous areas throughout Central Coast experienced flooding, with Cambria being one of the hardest hit. In fact, Cambria’s Fire Department used a boat to rescue people along Main Street.

Only time will tell if the Ides of March will bring wet weather. But a few of the models are advertising that the southern branch of the jet stream will shift southward in March and take a position over Southern California.

For the Santa Ynez Valley, that could mean storms releasing heavy rainfall — unless the jet stream moves too far south, leaving the Valley higher and drier.

I believe the heavier rainfall will come soon, and it should put a dent in the drought. But it won’t mitigate it. Water will always be a concern here in California.

John Lindsey is Pacific Gas and Electric Co.’s Diablo Canyon Power Plant marine meteorologist and a media relations representative. Follow him on Twitter @PGE_John.


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