Experts say La Niña still a player this winter
http://www.pe.com/localnews/stories/PE_News_Local_D_lanina23.29a81eb.html
12:04 AM PST on Thursday, December 23, 2010
By DAVID KECK
The Press-Enterprise
Weather-wise, 2010 may go down as the year of Murphy's Law.
From a milder-than-normal summer to a mid-autumn heat wave, nothing went like it should have. Now, a week of drenching rain over Inland Southern California has one of the world's foremost climatologists and teams of National Weather Service meteorologists scratching their heads, trying to figure out just what happened.
This was supposed to be a La Niña year, a condition when cooler-than-average equatorial waters in the Pacific bring drier weather to the southwestern United States during the winter.
Instead, rainfall since last Friday has broken December records across the area.
Scientists are sticking with their La Niña forecast, at least for now.
"It's the closest sure thing there is," said Bill Patzert, a climatologist at the Jet Propulsion Laboratories in La Canada-Flintridge. "But it sure doesn't look like it this week."
It may take researchers years to figure out the atmospheric abnormalities of 2010, which likely will cause a re-examination of global climate.
But before any serious debate can take place, Patzert and others warn that a La Niña winter still could pan out.
Brandt Maxwell, a National Weather Service meteorologist in San Diego, noted earlier this week that several studies have indicated La Niña may bring heavy autumn rains then a pronounced dry-out in January, February and March, typically the months that bring the most precipitation to Southern California.
Though the reasons are not fully understood, he said, the research indicates that many factors -- not just ocean temperatures at the equator -- influence annual rain patterns in Southern California.
For example, Maxwell said, unusually high air pressure over Greenland this fall may be connected to weather patterns that have brought colder-than-average temperatures to Europe and much of North America. That high pressure over Greenland appears to be breaking down, he said.
"That may mean it will dry out here," he said.
PRESSURE AT THE POLES
Patzert said unusually high pressure at the Earth's north and south poles may be contributing to abnormal weather in many places around the globe. He said there's still plenty of time for a La Niña to materialize.
On that point, he has history on his side: Of the 22 La Niña years recorded since 1949, 18 have exhibited the classic signs of colder, drier winter months in Southern California, he said.
"Even though we've had a wet December, it's like playing Texas Hold 'Em and we've only seen three cards so far," Patzert said by phone on Monday.
Patzert described the latest string of storms simply as a weather event that may or may not indicate a change in climate. But he also pointed out that California has experienced longer heats waves, lighter winter snow packs in the Sierra Nevada and 20 percent less water flowing in the Colorado River over the past 100 years.
That may or may not be the result of global warming due to man-made emissions, he said. It also may be the result of rising populations and urbanization, he said.
Southern California has become so densely populated and developed that widespread buildings, roads and other structures have caused massive concentrations of heat retention. Those heat islands could change atmospheric temperatures enough to affect climate across the Southwest, he said.
"Riverside and San Bernardino counties are excellent examples," Patzert said, noting the region's growth in recent decades.
Reach David Keck at dkeck@pe.com or 951-368-9856
http://www.pe.com/localnews/stories/PE_News_Local_D_lanina23.29a81eb.html
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