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Another weird and wild winter in the West?

NOVEMBER WAS ONCE A MONTH IN which the West as it moved toward winter could count on a few climatic certainties. Seattle and Portland residents zipped anoraks in preparation for five months of wet but clement weather. San Franciscans battened down the hatches for the first of those blustery rainstorms that were hell on eucalyptus limbs but heaven to municipal water districts. And Southern Californians said good riddance to autumn's combustive Santa Ana winds and welcomed the rain that colored their umber hills Christmas green.

You may have noticed that, lately, our weather has not been obeying the rules.

A year ago this month, Seattle was drenched by a rainstorm so ferocious the Lake Washington bridge sank. November floods were followed by December's freeze: a week-long blast of Arctic cold that turned Yakima into the Yukon, Portland into Point Barrow, and then descended Hun-like into California to burst pipes and ravage gardens from Petaluma to Pasadena.

Naive Californians hoped the cold might be accompanied by precipitation to end their five-year drought. But January was dry, February was dry, and it wasn't until March that late-season rains ameliorated the situation from desperate to merely dire.

This year we have a roused Philippine volcano. We may have El Nino. We have uncertainty. But the West also has some of the world's leading institutions of climate study. On these pages, we report on what they know and don't know about our weather, then show you how you can hone your own weather eye with a home weather station.


Take a late-afternoon walk to Point Loma or Point Reyes or Cannon Beach or Cape Flattery. Look west.

There, beyond the breakers in the 64 million square miles of Pacific Ocean, is where most of our weather incubates.

The prime mover behind all of it can be seen sinking toward the horizon. As the sun heats the Earth, continents and oceans warm unequally, which means that the atmosphere develops hot and cold areas. "And because the atmosphere likes to sustain equilibrium," explains Michael Pechner, a private meteorologist who consults for San Francisco's KCBS radio, "these hot and cold areas are constantly moving. That creates weather."

For the West, the prevailing weather pattern is from west to east, as Pacific-born storms travel eastward on the jet stream, a band of high-speed winds 30,000 to 40,000 feet above the planet's surface. In summer, the jet stream and storms stay north; in winter, they drop south, bringing winter snow and rain.


There are regional idiosyncrasies, of course--enough to keep local forecasters on their toes. Seattle's winter precipitation is dependable--on average, 5.6 inches of rain this month, 6.33 inches in December. But Puget Sound is an occasional stop on the "Pineapple Express," a flow of warm, moist air that begins near Hawaii. On board the express last year were Seattle's November floods. The city's freezing, blizzardy December was the product of another interloper. "Cold air came straight down from Canada and combined with moisture flowing into Puget Sound," explains Patrick Brandow of the National Weather Service office in Seattle. He adds, "Snow is the most difficult thing to forecast around here. It happens only once or twice as season, and the ingredients have to be just right."

Snowfall is likewise unpredictable along Colorado's Front Range. Says Colorado weather consultant Richard Medenwaldt, "What happens is we get cold air flowing down from Canada, pooling against the Rockies, forming a dam. Then a little innocuous storm comes in from the West, meets that cold air, and turns into something significant that puts down a foot of snow in Denver."



In some ways, forecasters in the West have a more difficult time than do prognosticators elsewhere. One problem is the dearth of data from the place where our weather is born, the Pacific. Meteorologists rely on satellites, buoys, and commercial shipping to obtain readings far out in the ocean. But the Pacific is so vast that large portions of it remain blank spaces on this data grid. Even our satellite vision is myopic: the United States is down to one aging Geostationary Operational Environmental Satellite (GOES). Its successor, GOES-NEXT, is not scheduled for launch until 1974.

Despite these difficulties, weather forecasting has made big strides in the 50 or so years since the development of radar and computers made modern meteorology possible. Some advances have been lifesaving. Researchers at the National Center for Atmospheric Research (NCAR) is Boulder, Colorado, have found ways to predict and detect microbursts--small-scale, short-lived, extremely powerful downblasts, by-products of thunderstorms--that pose grave danger for aircraft during landings and takeoffs. An NCAR-developed weather radar and wind shear alert system allows control towers to warn pilots of these previously invisible hazards. The system is already in place at Denver's Stapleton Airport and will be implemented around the country beginning in 1993.

Indeed, all our short-term forecasts have become more consistently accurate. The National Weather Service estimates that today's five-day forecasts are as accurate as three-day forecasts were 15 years ago, three-day forecasts the equivalent of two-day ones 10 years ago.



Visitors are welcome to tour NCAR's Boulder facility. (For visitor information, see page 52.) There they can view one of the world's largest, fastest computers.

The CRAY Y-MP can perform 2.5 billion calculations per second, on eight parallel processors. It contains 60 billion bytes of disk storage.

This supercomputer is one of the few computer systems devoted solely to modeling Earth's climate. It takes weather data from around the world and plugs it into a complex series of equations that approximate ocean, land, and atmosphere. There models are useful tools, especially for monitoring climatic changes over time, but are very rough mathematical sketches of an extraordinarily complex system. They can't predict in November that Boulder will be sunny on the afternoon of January 23 and snowy on the morning of March 5.

To predict further in the future, meteorologists depend less on mathematical models and more on records of weather of past years. "All of our seasonal forecasts come out of statistical inferences," says Jim Wagner, senior forecaster for the National Weather Servies's Climate Analysis Center. Averaged over the whole continental United States, Weather Service accuracy rates range from 65 percent for a 30-day temperature forecast in winter, down to 52 percent for a 9-day precipitation forecast for spring.

Probably the dean of long-range forecasting if The Old Farmer's Almanac, which celebrates its 200th anniversary this year. The contemporary Almanac's forecasts are the work of a Cal Tech-trained meteorologist, Dr. Richard Head, of Scottsdale, Arizona. "We look at correlations between what has occurred in the past and what is occurring now," Head says. "Solar activity--sunspots, magnetic storms, changes in the sun's radiant energy--and other things like the snow and ice cover on Earth." He estimates his accuracy rate to be 65 to 70 percent.


No better example of long-term forecasting's limits can be found than in attempts to understand California's drought. Some regions of the Golden State have not enjoyed a "normal" year of rainfall since 1986. This year, even with late-winter rains, the U.S. Bureau of Reclamation anticipates 1992 water deliveries at no more than 50 percent of usual.

The immediate cause of California's past five dry years was a series of high-pressure systems stalled over or just off the California coast. These highs blocked, diverted, or split the jet stream; raindrops that in other winters might have fallen on Marin or Monterey fell instead on British Columbia, Baja California, or far out in the Pacific.

But what has caused the high-pressures systems to linger so long? Says Dr. Daniel Cayan, climatologist at the Scripps Institution of Oceanography in La Jolla, "One of the really tantalizing aspects of weather is that we find a recurrence of its large-scale patterns. It's as if the atmosphere has some kind of memory. If we could isolate the elements that make up the memory, we might know what causes the high pressure to persist instead of breaking down." But, he adds, "It's very hard to identify chicken and eggs, the ultimate causes for a system that's interconnected and continuous the way the climate system is."

Drought-watchers have paid much attention to the El Nino/Southern Oscillation, the patch of warmer-than-normal surface water that materializes in the western Pacific and slowly drifts eastward toward South and Central America. The last strong El Nino, in 1982, coincided with a record wet winter in California; much hope has been voiced that its reappearance would herald another year of bounteous precipitation. But Cayan notes that California's current dry spell occurred both during El Nino years and during years dominated by its cold-water sibling, La Nina.

Many climatologists also caution that Californians may have been lulled by a series of rainier-than-normal decades into thinking that their state is less dry than it really is. "Californians should realize that a five-year drought is normal," says weather consultant Michael Pechner. "There are data--tree rings, core samples from glaciers--that show droughts that have lasted 20 years over the last several hundred years."


What does this winter have in store? At our press time, evidence was building that an El Nino condition had begun in the tropical Pacific. The June eruption of the Philippine volcano Mount Pinatubo had spewed a cloud of sulfur dioxide and other gases into the stratosphere; the cloud from the last comparable eruption, that of the Mexican volcano El Chinchon, cooled global temperatures by an estimated 1 [degrees] back in 1982. But the chance of temporarily cooler temperatures has not erased fears of global warming; it remains a major focus of research at Scripps, NCAR, and other institutions.

Sunset asked a trio of forecasters to share their predictions for the winter of 1991-92:

"California's winter--specifically November--will start out wet," forecasts Michael Pechner. "The unknown equations are, one, Mount Pinatubo, and two, the fact that we're beginning to see a warm El Nino episode off the Central and South American coast. The last time that happened, we had two of our wettest winters back to back. Those two factors could point to a wetter winter for California."

In Colorado, forecaster Richard Medenwaldt predicts, "The Front Range of the Rockies can expect an early and cold start for winter, which generally translates to warmer temperatures and less than usual precipitation for the West Coast."

Finally, Dr. Richard Head and The Old Farmer's Almanac foresee that the desert Southwest will have a winter "considerably colder than normal," and California one "much colder than normal, with above-normal snowfall, particularly in the central Sierra Nevada and Southern California mountains."

The winter of 1991-92--warm? cold? snowy? dry? Save this magazine until April, and see which of our experts came closest.
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Copyright 1991 Gale, Cengage Learning. All rights reserved.

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Title Annotation:includes information on setting up a home weather station
Date:Nov 1, 1991
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