Ag Weather Forum

The following article, by reporter Paul Rogers of the San Jose California Mercury-News, has a good summary of the effect felt in California from the current extreme drought. The article also has some discussion about a long-term temperature feature in the north Pacific--a negative trend in the Pacific Decadal Oscillation, which may be a major factor in the drought's intensity. I have noted the negative PDO in long-term weather discussions both here and in presentations during the past couple years.--Bryce

Twitter @BAndersonDTN

In a new dose of bad news for a state growing increasingly concerned about lack of rain, California's historically dry weather is expected to last for at least another three months, federal scientists said Thursday.

The dire forecast for the rest of the state's winter rain season came as federal officials classified much of California as being in "extreme drought." And the Obama administration declared 27 California counties, including most of the Bay Area, as "natural disaster areas," eligible for emergency federal loans for farmers.

Computer models based on data from satellites, buoys in the Pacific Ocean and other sources favor below-normal levels of rainfall for California, much of Nevada, Arizona, New Mexico and West Texas until April, according to a new report from the National Weather Service's Climate Prediction Center.

"There will be a few precipitation events, but we're looking at drier-than-normal conditions in February, March and April," said Matthew Rosencrans, a meteorologist with the agency, which is based in College Park, Md. "Right now we are saying the odds do not indicate a Miracle March, which is not a good thing."

To be sure, long-range forecasts are not as accurate as short-term weather forecasts. The 90-day precipitation outlook for the West has turned out to be right about 60 percent of the time over the last 20 years.

Gov. Jerry Brown was expected Friday in San Francisco to declare a drought emergency, which would make it easier to transfer water between different regions of the state, and raise awareness for conservation.

Meanwhile, the U.S. Drought Monitor, a weekly update of drought conditions by federal agencies and researchers at the University of Nebraska, classified large sections of Northern California, including the Bay Area, as the fourth most severe of five drought categories: "extreme drought."

"It means that things are not getting better. They are getting drier," said David Simeral, a meteorologist with the Western Regional Climate Center in Reno, who is part of the Drought Monitor team.

"We're starting to see a lot more impacts showing up around the state," he said. "Groundwater issues, low snowpack, less forage available for cattle grazing, more fire risk."

Farmers in 27 California counties -- including Santa Clara, Alameda, Contra Costa, Monterey and San Benito -- declared "natural disaster areas" and in eight adjacent counties -- including San Mateo and Santa Cruz -- can now receive low-interest federal loans.

"Our hearts go out to those California farmers and ranchers affected," U.S. Agriculture Secretary Tom Vilsack said.

Last week, 27 percent of California's land area was listed as being in "extreme drought." This week it is it is 63 percent -- the most since the Drought Monitor began 14 years ago.

California is a historically arid place. Los Angeles and San Jose, for example, each get about 15 inches of rain in an average year. That's the same amount as Casablanca, Morocco. The state has periodic droughts but has not suffered a sustained one since 1987-92.

Increasingly, political leaders and scientists are concerned that California is entering another such period. Sierra Nevada snowpack on Thursday was 17 percent of normal. Last year, most cities in the state received the lowest amount of rain in any living person's lifetime -- with records going back to 1850.

Although smaller water agencies, such as in Willits, in Mendocino County, where there is just a 100-day supply of water left, are struggling, most large Bay Area water districts have not called for rationing and don't plan to make a decision until March or April. Years of rebates for conservation and increased storage -- both underground at places like the Santa Clara Valley Water District, and in reservoirs, like the recently expanded Los Vaqueros Reservoir in Contra Costa County -- have put them in better positions than during previous dry spells, they say.

"We are in fair shape and examining our options. But we've been planning for this for a generation," said Abby Figueroa, a spokeswoman for the East Bay Municipal Utility District.

For the past 13 months, a huge ridge of high-pressure in the atmosphere has sat off the West Coast, blocking storms that normally would bring rain during winter months.

Such high-pressure zones normally rise and break down as temperatures change and the jet stream shifts every winter, but this one has been different. Some scientists say it may be linked to climate change, which has melted polar ice and warmed the oceans. Others, including many who strongly support the broad scientific consensus that the Earth is warming due to human burning of fossil fuels, say it is too early to know. It may be related to other factors, such as naturally occurring temperature fluctuations in the Pacific Ocean, similar to El Niño and La Niña, or simply random bad luck.

Part of the National Weather Service's 90-day dry outlook, however, is based on the fact that there is a large section of the North Pacific Ocean where water temperatures now are 4-5 degrees Fahrenheit warmer than the historic average, Rosencrans said. And water along the California coast is about 1 degree cooler than average -- a condition known as a negative Pacific Decadal Oscillation, which historically has been linked to more high pressure, and drier weather in years past.

Full article with graphics is here: http://bit.ly/…

(ES/AG/CZ)

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