A strengthening La Niña influenced weather patterns that sent Alaskan temperatures dipping to -74 F and wind chills to -90 F in late January and early February, and brought flooding and heavy snow to the West, warmth to the East, and extreme weather from South America to Asia, according to National Oceanic and Atmospheric Administration scientists.

In May 1998, a rapid cooling of the near equatorial waters in the central Pacific signaled the end of the 1997/98 El Niño and the beginnings of a La Niña. La Niña features colder-than-normal sea surface temperatures in the tropical Pacific Ocean. Many forecast models indicated this transition and that the La Niña would continue to develop. Now, six months later, scientists at the National Weather Service's Climate Prediction Center, a NOAA facility in Camp Springs, Md., say that the event has grown into one of the strongest La Niña episodes of the past 50 years.

"This La Niña provides the physical link between many of the unusual weather patterns seen recently in far-flung parts of the globe," said John Janowiak, a NOAA scientist. "While parts of Alaska have experienced severe cold, most of the lower 48 states, especially those in the southern tier, have enjoyed record breaking warm temperatures."

The Alaskan cold snap can be blamed on persistent winds bringing bitterly cold air from north of the arctic circle southward to Alaska. According to National Weather Service scientists, this circulation pattern is frequently associated with La Niña, which usually results in colder than normal winter weather over Alaska. Forecasters predicted the below-normal winter temperatures for Alaska as early as September.

Except for California, the rest of the lower 48 states experienced a much warmer-than- normal November 1998 through January 1999. Temperatures in many states ranked within the 10 warmest November-January periods of the century. The United States, as a whole, experienced the third warmest November-January of the past 104 years. As a result, the United States, as a whole, saw a 10 percent energy savings, more than a 20 percent savings over the southern-tier states, and a nearly 50 percent savings in Florida, according to the weather service.

The La Niña contributed to the series of huge storms that hit the Pacific Northwest, and blasted Washington, Oregon, and northern California with hurricane-force winds, heavy rains and mountain snows. As a result, many sections of the northern-tier states in the West have experienced precipitation totals that are in the top 10 of this century. Meantime, sections of the Southwest suffer from lack of precipitation.

The global La Niña impacts include heavy rains, severe storms, and flooding in southern Africa, drought in Kenya and Tanzania, flooding in the Philippines and Indonesia, and abnormal wetness in northern South America. The same regions suffered the opposite impacts during the 1997/98 El Niño.

As for the cold wave in Alaska, it lasted from Jan. 26 to Feb. 13, during which time Fairbanks recorded a record 19 consecutive days with a low temperature less than
-35 degrees F. In contrast, temperatures the following week were actually well above normal across the state. "High temperatures actually exceeded zero during the weekend following the cold snap and even rose to a much-above-normal reading of 24 degrees F on President's Day, Feb. 15," said Lee Kelley, the meteorologist-in-charge of the National Weather Service Forecast Office in Fairbanks. This week, temperatures are seasonably cold. Readings Tuesday morning ranged from -15 to -30 degrees F over the Alaskan interior, and seasonable cold is expected for the rest of the week. At Fairbanks, the normal high temperature is 11 degrees above zero and the normal low is 12 degrees F below zero.

Alaskans should not have let the last week's abnormal warmth make them too complacent. The National Weather Service's long-range forecasts indicate that the odds favor below-normal temperatures during the March-May time frame when La Niña impacts will still be in force.

Current forecasts, graphics and observations are available on the Internet at http://www.cpc.noaa.gov