You may want to keep your umbrella handy
By John LindseySan Luis Obispo Tribune
Published: Sunday, Jan. 23, 2011
This year, the rainy season has been quite unpredictable and has delivered mixed results, from an overabundance of rain during December to a nearly dry January as La Niña continues to strengthen.
The Central Coast is just about at its halfway point of the rainfall season, and things could be changing again.
La Niña, which generates cooler-than-normal sea surface temperatures in the central and eastern equatorial Pacific, usually produces below-normal rainfall along the Central Coast.
An El Niño condition —warmer-than-normal ocean water in the equatorial and eastern Pacific — usually produces above-normal rainfall.
Both of these oceanographic phases are considered to be a standing pattern. In other words, they stay fixed in the same geographic area. These phases usually last for about a year or so.
Unlike El Niño and La Niña, the Madden-Julian Oscillation is a large traveling pattern of increased rainfall and thunderstorm activity that propagates eastward at approximately 8 to 18 mph across the tropical parts of the Indian and Pacific oceans.
This cycle usually lasts between 30 and 60 days.
In 1971, Roland Madden and Paul Julian stumbled upon this pattern when analyzing wind anomalies in the tropical Pacific.
But little attention was paid to the oscillation until the strong 1982-83 El Niño event, which led researchers to believe that this pattern may have enhanced the amount of rain in California.
The Madden-Julian Oscillation is also called the "30 to 60 day oscillation" and the "30 to 60 day wave."
The latest Madden-Julian Oscillation forecast from the Climate Prediction Center in Silver Spring, Md., indicates an oscillation is present in the western Pacific and is strengthening.
There is growing evidence that what happens in the tropics can influence our weather along the Central Coast.
Models suggest that the oscillation will travel eastward. Historically, especially during La Niña phases, as the Madden-Julian Oscillation moves across the Pacific Ocean, a split in the polar jet can develop.
The southern branch of the polar jet can extend far out over the Pacific toward the coast of California. This river of air in the upper-atmosphere can steer moist, subtropical air toward California and can bring several days of rain.
If this scenario develops, rain may be in the forecast by early to mid-February.
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