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Mild Winter, Average Rainfall Are Forecast

December 03, 1987|H.G. REZA | Times Staff Writer

Mild temperatures and average rainfall are in store for Southern California this winter, but the East Coast and South can expect a colder than normal winter, and heavy precipitation will visit an area stretching from southern Arizona to Florida, Scripps Institution of Oceanography researchers predicted Wednesday.

The forecast by weather scientists Jerome Namias and Dan Cayan is the annual 90-day winter prediction released in December by the Experimental Climate Forecast Center at Scripps. The three-month forecast covers the period from December to February.

For water-starved California, which faces a water shortage next year in the southern part of the state, the forecasters indicated that recent winter storm activity in Alaska may bring enough rain and snow to head off a crisis.

Namias, a veteran meteorologist, has been making annual winter predictions since 1974. Cayan, who has worked with Namias since 1977, said the forecasts are painted "with a broad brush" and do not attempt to predict weather conditions on a particular day or week.

"We're forecasting averages over 90 days," Cayan said. "Probably the only things we'll be able to capture are major variations, average conditions--meaning above normal, below normal, heavy, light, wet, dry, those kinds of things. All of these variables have special dimensions of thousands of kilometers over the United States."

With those multiple qualifiers in mind, Namias and Cayan are predicting a colder than normal winter in the eastern half of the nation but a relatively mild one out West. This winter's weather patterns will dump heavy precipitation along the southern Atlantic Seaboard and from the California-southern Arizona border to Florida, Cayan said.

Normal rainfall and snow is expected in a wide area from the western Central Mountain States to New England, and temperatures are also expected to hover around normal in most of these areas.

However, Namias and Cayan are predicting dry winters in the Midwest, the Mississippi Valley and in the extreme Northwest.

"The precipitation is based on the evolution of this fall's wind and weather pattern, which was marked by warm and dry conditions over the Northwest and cool weather in the Midwest and South . . . frequent ridges in the upper wind jet stream are expected over the interior Northwest, which should keep temperatures in the West mild," Namias said.

Coastal waters in California have been relatively warm during the fall, Cayan said. This will translate into mild winter temperatures along the Southern and Central California coast. For Southern California this means that air temperatures will average about one degree warmer, but may rise as many as four degrees above normal. However, rainfall is expected to be normal.

Outlook Uncertain

For Northern California, the forecasters say the outlook is uncertain. On the one hand, the forecasters were hopeful that early "vigorous winter storm activity" in the Gulf of Alaska can bring "sufficient" rain to the northern part of the state. But Cayan warned that a persistent high-pressure ridge that sits over northern Idaho could produce drying trends this winter in the Northwest and this could affect California's water supply.

"High pressure means a lack of storms and clear, dry weather in the region," Cayan said.

On Tuesday, State Water Project officials expressed hope that recent winter storms that hit Northern California will help avert a water shortage in Southern California in 1988. Water experts have cautioned that unless this winter's rainfall and snowpack are substantial, a drought situation similar to the one that existed in 1977, when water was rationed, could exist next year.

State water experts labeled the winter of 1986-87 critically dry, and precipitation in California this year has been less than normal.

Mild coastal temperatures that are predicted this winter can be attributed to a large pool of warm Pacific Ocean surface water that runs from Mexico north to the Gulf of Alaska, said Cayan. Simultaneously, there is a large pool of colder than normal water located in the Central Pacific Ocean, he said.

Cayan called the center's winter weather predictions last year "a mixed bag." They accurately predicted the precipitation in the Gulf Coast area and on the Eastern Seaboard and drier than normal conditions in the Midwest, he said, but failed miserably in the West, and particularly in Northern California.

"Frankly, in the West we did not do well, even though we did OK in Southern California, where it turned out to be normal, which we forecast. In the northern part of the state it turned out to be dry, when we forecast wet . . . A winter can be very changeable. For this reason, sometimes it doesn't make sense to predict for three months," he said.

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