Saturday, November 30, 2013

[californiadisasters] Dry winter ahead, state’s experimental forecast warns

Dry winter ahead, state's experimental forecast warns

Published: Friday, Nov. 29, 2013 - 1:20 pm
Last Modified: Saturday, Nov. 30, 2013 - 12:31 pm

Despite a hint of rain and snow in the forecast next week, the Sacramento region and California as a whole can expect a third dry winter ahead.

That's according to an "experimental" long-range forecast released this week by the California Department of Water Resources. The forecast covers the 2014 water year, which runs from Oct. 1, 2013, through Sept. 30, 2014. It calls for "mostly dry conditions for most of California," with dry conditions being especially likely in the south state.

The forecast was done for the state by Klaus Wolter, a Ph.D. meteorologist and research associate at the Cooperative Institute for Research in Environmental Sciences, at the University of Colorado, Boulder.

Wolter made a similar dry prediction for the state last year, which at first appeared "destined for failure," he said. That was because December 2012 was extremely wet, partly due to the arrival of a series of atmospheric river storms. Such storms tap into tropical moisture in the far western Pacific Ocean and channel it into a narrow stream often aimed like a fire hose directly at California.

"However, the remainder of the season was record dry, producing an overall result of dry for the water year," Wolter said in a statement.

In a hint that suggests a similar outcome this year, the near-term forecast calls for a major change in the weather for Sacramento and Northern California on Monday. A storm is expected to drop out of the Pacific Northwest, bringing a chance of rain to the Valley through Wednesday and snow in the Sierra Nevada through Thursday.

But don't get too excited yet.

"It's a fairly dry system, so it doesn't look like a whole lot," said Craig Shoemaker, a meteorologist at the National Weather Service in Sacramento. "It doesn't have a really deep moisture plume."

Temperatures are also predicted to drop sharply with the storm. Overnight lows in Sacramento could get as cold as 34 degrees on Wednesday night.

Shoemaker said the storm could generate as much as 8 inches of new snow in the Sierra Nevada, where most ski resorts still have limited terrain open, if they are open at all. The snow level could drop as low as 2,000 feet on Tuesday night.

State officials intend the experimental forecast to help residents, business owners and policymakers prepare for winter.

The National Weather Service typically does not make a detailed long-range winter weather forecast. Its Climate Prediction Center, however, does offer a less specific three-month forecast. The most recent, issued Nov. 21, indicated neither wet nor dry conditions for California.

A third dry winter could have severe implications, since most of the state's water storage reservoirs are severely depleted after two drought years. California is heavily dependent on winter storms for the water supply it needs to survive summer. The state typically depends on just three months – December through February – for half its annual precipitation, although freak storms in other months can make a big difference,

As for the winter ahead, state officials caution the final outcome is difficult to predict, partly because neither El Niño nor La Niña conditions dominate in the Pacific Ocean this year. The former condition indicates the ocean is warmer than average, while the latter is cooler. A strong signal in either direction can make predictions easier.

This winter, forecasters say the ocean will be in a "neutral" condition, though Wolter said it could shift into an El Niño pattern by springtime.



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