Heavy precipitation is an El Niño surprise

This winter's much-anticipated El Niño phenomenon has not been behaving exactly as anticipated.

As fall approached, atmospheric scientists were watching developments in the tropical Pacific Ocean. A large batch of unusually warm water had materialized that stretched from the International Date Line eastward to Peru.

It was a signal that the first El Niño in six years was on its way. And if it merged with the warm blobs of water already in place in the eastern Pacific when it arrived, some forecasters warned this El Niño might be a whopper.

El Niño is the warm phase of the El Niño Southern Oscillation (ENSO) that alters weather patterns worldwide. It tends to produce warmer and drier winters in the Pacific Northwest, cooler and wetter conditions across the southern tier of states from southern California to the Deep South, and milder weather in the Midwest and New England. This is particularly true when El Niño is strong.

There are a variety of indices used to determine the phase and strength of the ENSO. Two of the most widely used are the Oceanic Niño Index (ONI) and the Multivariate ENSO Index (MEI). The ONI is based on sea-surface temperature departures from average in the central tropical Pacific Ocean, while the MEI combines sea-surface temperatures with five atmospheric measurements.

Klaus Wolter of the National Oceanic and Atmospheric Administration (NOAA) believes the MEI is better for monitoring ENSO than other methods.

"In brief, the MEI integrates more information than other indices, it reflects the nature of the coupled ocean-atmosphere system better - and it is less vulnerable to occasional data glitches in the monthly update cycles," explains Wolter.

There have been two super-El Niños since 1950. They occurred during the winters of 1982-83 and 1997-98. The ONI ranked the 1997-98 event the stronger of the two at 2.3, while the 1982-83 El Niño came in at 2.1. Both events were of equal strength on the MEI scale with a value of 3.0. A few climate experts were entertaining the possibility that the current El Niño may eventually equal, or even exceed, the strength of these monsters.

That was the forecast approximately two months ago, but where do we stand now? Is the winter weather unfolding as expected?

Well, not exactly. It appears that the typical El Niño weather pattern hasn't kicked in yet.

The biggest surprise so far has been the heavy precipitation in Washington and Oregon that has caused flooding and landslides in some areas.

"Of all the years in which there was a strong El Niño present in the tropical Pacific Ocean, this is the wettest start to any of those years that we've observed in the Pacific Northwest, both in Portland and Seattle," said Daniel Swain, a climate scientist at Stanford University.

These storms are also impacting Central Oregon. In Sisters, temperatures were below normal in November and precipitation registered more than a third of an inch wetter than average.

During the first 18 days of December, the anomalies have been even greater. Temperatures are 4 degrees Fahrenheit above average while precipitation levels are already 1.26 inches above normal, with more than a third of the month left to go.

And, yes, the Central Oregon Cascades are finally getting some much-needed snow.

According to Marilyn Lohmann, forecaster at the National Weather Service in Pendleton, the snowpack is currently 80 to 100 percent of normal. Lohmann also noted that total precipitation levels in the mountains are 120 to 130 percent of normal, indicating that a significant amount of rain has also fallen there.

The recent unusual warmth from the Midwest across to the Eastern Seaboard, and the wetter-than-normal conditions in the southern states seem to be more in line with El Niño-like weather. But Mike Halpert, deputy director of NOAA's Climate Prediction Center, said El Niño isn't to blame for these current weather trends. Halpert thinks the heat in the Northeast is due to the Arctic Oscillation (AO). When the AO is in its positive phase, as it is now, a strong jet stream keeps the coldest air trapped in the polar regions.

"While it has certainly been mild across the country, it's not really something we would attribute to El Niño," said Halpert. "The AO is probably playing a bigger role this time."

For Californians desperate for water, Halpert believes the rains will begin there soon.

"People are wondering where the rain is. Don't panic," Halpert said. "The time when we are really looking for the rain is after the first of the year. We still expect January-to-March to be wetter than average throughout the whole state."

For the three-month period January-March 2016, NOAA's Climate Prediction Center foresees above-normal temperatures in the Pacific Northwest and below-normal precipitation, except in southwestern Oregon where rainfall amounts should be near average.

If the current El Niño doesn't strengthen from its current level, it will go in the books as the third strongest event in 65 years, behind only the 1997-98 and 1982-83 episodes. It is expected to weaken over the next month or two, then fade to neutral by late spring or early summer.