La Niña gets the credit for near-record rainfall

Sean C. Morgan

Of The New Era

The Sweet Home area had more than seven and a half times the amount of rain last month that fell during the same period last year, all part of the effects of a La Niña condition announced last week by NOAA.

In January 2005, the Army Corps of Engineers reported 1.85 inches of rainfall. This year, the Corps recorded 14.18 inches of rainfall in January.

Tiffany Brown, an intern meteorologist with the National Weather Service office in Portland, said her office did not have information on Sweet Home, but nearby Eugene had 12.68 inches of rain in January, the seventh wettest year on record, edging out 1967’s 12.67 inches of rain.

Eugene had one record day of rainfall, Jan. 17, with 2.37 inches of rain, Brown said. The Corps reported 1.87 inches in Sweet Home that day, which was the heaviest rainfall of the month and led to some isolated local flooding.

On Feb. 2, the National Oceanic and Atmospheric Administration announced La Niña conditions across the globe. La Niña is a condition in which water temperatures in the eastern Pacific, including off the coast of Oregon, are cooler than normal. The opposite effect, El Nino, occurs when Eastern Pacific water temperatures are above average. Both conditions are believed to lead to weather conditions, including drought and correspondingly heavy rainfall in various parts of the world, when they occur. The last La Niña occurred in 1995.

“Typically, with La Niña, we have a little more rain,” Brown said. “And it’s drier in other parts of the country. We weren’t expecting it, but we should have been because we were so dry (in recent years).”

Going into the winter, officials were expecting a neutral winter, with neither a La Niña nor El Nino condition, Brown said. The Northwest can expect more rain, perhaps one or two more major storms going into the spring, she said.

The Corps cannot say yet what the reservoirs will look like next summer, spokeswoman Heidi Helwig said. Up until Feb. 1, the reservoirs were being used for flood control.

The Corps will either allow reservoirs to fill or release water to reach the Corps’ rule curve for each reservoir, Helwig said.

The rule curve sets the water levels the Corps target for the reservoirs throughout the year to meet the demands of various uses, such as those placed by the Endangered Species Act for downstream fish or to be ready for flood control.

“We do have a lot of snow pack, which is a good thing,” Helwig said, but it still remains early to predict conditions this summer.

With the rainfall so far, “it has all the makings of a normal to good water year,” Helwig said.

Agency forecasters predicted a La Niña condition was forming nearly three weeks ago, according to NOAA. During La Niña, ocean temperatures in the central Pacific Ocean are -0.5 degrees Celsius from normal over a three-month period.

“This pattern will favor continued drought in parts of the South and Southwest, from Arizona to Arkansas and Louisiana and above-normal precipitation in the Northwest and the Tennessee Valley area,” said Vice Admiral Conrad C. Lautenbacher, undersecretary of commerce for oceans and atmosphere and NOAA administrator.

Internationally, La Niña impacts during the northern hemisphere winter typically include enhanced rainfall across Indonesia and northern Australia as well as in the Amazon Basin and in southeastern Africa and below-average rainfall across the eastern half of the equatorial Pacific and eastern equatorial Africa.

It typically favors increased Atlantic hurricane activity, said Jim Laver, director of the NOAA Climate Prediction Center.

“It is too early to say with confidence what effects this La Niña event will have on the 2006 hurricane season,” Laver said.

La Niña recurs every three to five years. The last La Niña occurred in 2000-2001 and was relatively weak compared to the 1998-2000 event.