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.
THE PINEAPPLE EXPRESS RUNS INTO A SNOWBANK
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."
SCANNING THE OCEANS, SPYING
ON THE WINDS
In some ways, forecasters in the West have a more difficult time than do prognosticators elsewhere. …