Scientists are predicting a wet winter across the Northwest and a dry one in the Southwest after discovering the reappearance of La Nina in the Pacific Ocean.
A U.S.-French satellite earlier this month detected a pool of unusually cool water in the eastern North Pacific, and warm water in the western and mid-latitude Pacific.
"These unbalanced conditions will undoubtedly exert a very strong influence on climate over North America this fall and winter," oceanographer William Patzert of the Jet Propulsion Laboratory said this week.
The observations by the U.S.-French Topex-Poseidon satellite came three months after La Nina appeared to be fading away.
La Nina is characterized by unusually cold sea-surface temperatures in the eastern and central Pacific, which trigger atmospheric patterns that influence weather around the world. La Nina is linked to cooler conditions in central North America, and dry, warm conditions in the Southern states.
Last year's La Nina contributed to a series of huge storms that blasted Washington, Oregon and northern California with hurricane-force winds, heavy rains and mountain snows, and caused powerful storms elsewhere in the world.
According to Patzert, "From San Francisco to Seattle, they'd better batten down the hatches."
For the Southwest, Patzert forecasts a potentially dangerous dry spell: "One of the hangovers of the second year of La Nina is that we'll have to start watching our water, and we're probably going into a second year of quite volatile fire seasons."
Does the reappearance of La Nina indicate a long-term transformation of global weather patterns?
"Clearly, these unusual conditions, which have persisted for two-and-one-half years, will not be returning to normal anytime soon," Patzert said. "This climate imbalance is big and we're definitely going through a decade of wild climatic behavior."
Last winter's La Nina followed the historic 1997-98 El Nino, and was blamed for heavy snow in the West, massive flooding in Africa and severe drought in Asia.