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, these 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 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.”
They can certainly increase rainfall totals along the Central Coast. Historically, March in San Luis Obispo County can be wet — averaging about 3.4 inches of rain.
But 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 that stretched to Hawaii.
The rain began to fall early on March 9 and continued through the next day, producing amazing 24-hour rainfall totals. They ranged from a low of 3.4 inches in Pismo Beach to 11.6 inches in Santa Margarita.
The stalled cold front was accompanied by gale- to storm-force (55- to 73-mph) southeasterly winds in the coastal regions of San Luis Obispo County. San Simeon reported sustained wind speeds of 70 mph with gusts reaching 88 mph, while the Diablo Canyon meteorological tower reported peak sustained winds of 58 mph with gusts reaching more than 65 mph.
These winds produced a great amount of orographic enhancement, as the air mass is lifted up over our coastal mountains (upwind), it cools and eventually reaches its dew-point temperature. When this occurs, rain will develop on the windward side of the mountain. Like squeezing a wet sponge, moisture from this air mass is released in the form of precipitation. Some locations in the hills above Cambria and along the Cuesta Grade reported rainfall amounts exceeding 12 inches over 24 hours. Areas throughout San Luis Obispo County 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.
A review of this event indicates that an El Niño condition was present in the eastern Pacific Ocean, a much weaker event than the one we’re experiencing this year.
Only time will tell if the Ides of March will bring wet weather, but Caltech’s NASA Jet Propulsion Laboratory climatologist William Patzert hypothesizes that the southern branch of the jet stream will shift southward and take a position over Southern California in March. That late peak of the current El Niño event looks more and more likely to occur. While I believe the heavier rainfall will come soon, and it should put dent in the drought, it won’t mitigate it. Water will always be a concern here in California.
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The last major El Niño storm season in 1997-98 created widespread flooding and caused power outages impacting more than 1 million PG&E customers. PG&E has been preparing for storms like those, while urging its customers to be ready for natural disasters. That includes having a family emergency plan and keeping emergency kits for your home, your office and your vehicle. PG&E offers emergency-preparation tips on its website at www.pge.com/en/safety/preparedness/index.page.