Orange County Register

Orange County, which has been in a moderate drought for months, could experience below average rainfall for a third consecutive year, making the region more prone to wildfires, says Bill Patzert, a Jet Propulsion Laboratory climatologist.

(Click for today’s forecast).

John Wayne Airport rainfall

“I believe that the multi-year pattern known as the Pacific Decadal Oscillation, which suppresses storms in our area during its (present) negative phase, will be the dominant player this winter,” Patzert says. “I forecast a 50 percent to 70 percent chance of normal rainfall for Orange County.

“Remember, going back to march, we really haven’t had ‘real’ rain yet. In the Santa Ana wind/rainfall race the winds are winning … The offshore high-pressue system will dominate the storm tracks and drive most storms to the north of Orange County. As always, a cut-off low or two is possible, but that will not be the norm.

“So far, John Wayne Airport (Irvine) has had 0.26 percent of rain since 1 July (23 percent of normal to date). The spring, summer and fall have been super dry and, unfortunately, the short-term and long-term outlooks are also dry.”

Patzert’s prediction — and that’s what it is, a prediction — doesn’t mean that the county won’t receive periods of heavy rain this winter. He’s saying that it’s likely to a spot like John Wayne will receive normal rainfall, which amounts to about 13 inches between July 1 to June 30 each year.

He ties the forecast to the poorly understood Pacific Decadal Oscillation, which scientists describe as “a long-lived El Nino-like pattern of Pacific climate variability, because both have similar climate fingerprints. But, the PDO can last a great deal longer, 20 to 70 years, unlike El Nino or La Nina that typically persist less than 18 months. Also, while sea temperatures change most dramatically near the equator during El Nino or La Nina, the most drastic changes are typically seen in the North Pacific with the PDO.

“These shifts in location of cold and warm water in the Pacific alter the path of the jet stream, the conveyor belt for storms across the continent. Changes in the jet stream result in considerable, long-term changes in weather patterns. ” (Click for source material.)

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