El Niño predictions don't bode well

After two winters in a row of warm and extremely dry weather here in the Pacific Northwest, many residents have more than a passing interest in the forecast for the upcoming 2015-16 season.

They want to know if a more normal winter is in the offing that might alleviate worsening drought conditions and put some snow in the mountains. According to a growing number of meteorologists and climatologists the answer is probably no.

There is mounting evidence that a strong El Niño is developing in the central and eastern Pacific Ocean. Should this actually occur, it will likely impact various regions of the country in different ways. In California it's a good news/bad news scenario. A more northerly displaced subtropical jet stream should carry moisture-laden storms across the southern part of the state, helping to ease the extreme drought. But too much rain can also cause a lot of damage from mudslides.

In the Midwest and East Coast it means a reduced chance of frequent and prolonged outbreaks of arctic air. And the Gulf Coast and Eastern Seaboard should see fewer hurricanes.

For the Pacific Northwest, however, it means more of the same.

For the past several months, ocean temperatures in the tropical Pacific, stretching from about the International Date Line to just off the coast of Peru, have been steadily warming. At the same time the normal easterly trade winds have weakened and may even reverse direction and start blowing from the west. These are indications that a healthy El Niño may indeed be on the way.

The El Niño Southern Oscillation, or ENSO, is the single most important coupled ocean-atmosphere phenomenon to cause global climate variability. It describes the see-saw pattern of reversing atmospheric pressure between the eastern and western tropical Pacific that causes warm surface water to slosh back and forth.

An El Niño is said to exist when warm ocean water migrates eastward, pooling in the eastern Pacific Ocean. It's a La Niña if strong trade winds move the warmer water into the western Pacific. Both conditions disrupt normal weather patterns, to a greater or lesser degree, at many locations throughout the world.

Various indicators are used to determine the condition and strength of the ENSO, but perhaps the most widely used is the Multivariate ENSO Index (MEI). The MEI combines the effects of atmospheric pressure, wind, air and water temperature and cloud cover. When the numerical value is between -0.5 and 0.5 the ENSO is said to be neutral. An El Niño is rated weak in the range between 0.5 and 0.75, moderate between 0.75 and 1.0, and strong when the number is greater than 1.0. The same scale is used to grade La Niñas, except the numbers are negative.

It turns out that winters here in the Pacific Northwest and northern Rockies are more strongly correlated to the ENSO than almost anywhere else in the country. During an El Niño winter, warmer and drier conditions prevail about 65-75 percent of the time. During very strong El Niños that likelihood goes up to 80 percent, according to information from the Western Regional Climate Center (WRCC) in Reno, Nevada.

The two strongest El Niños in the last 65 years occurred during the winters of 1982-83 and 1997-98. In both cases the maximum MEI value was 3.0.

These very powerful events, though, can behave differently from the typical El Niño. For example, during the record El Nino of 1982-83 the subtropical jet shifted so far to the north that it brought heavy precipitation and warm temperatures to Oregon and Washington. According to Kelly Redmond of WRCC, it was the only major exception in the last 70 years to the typically dry El Niño winters expected in the Pacific Northwest.

The current MEI value for the two-month period June-July 2015 is already 1.972, and many scientists say it will likely increase in the next few months.

So, it does look like the upcoming winter will be warm and dry. But what about the two previous winters? They were warm and extremely dry too, but the ENSO was neutral. Why? After being gone for six years, El Niño is returning, only to find that another weather-related entity currently occupies the ocean waters.

A mysterious accumulation of usually warm water off the coast of the Pacific Northwest began to emerge late in 2013. Originally, "the mass of water was 1,000 miles long, 1,000 miles wide, and 300 feet deep, with temperatures 2 to 7 degrees F above normal," says Washington State climatologist Nick Bond. He dubbed it "the blob."

In 2014, more blobs appeared.

"The whole pattern is, we really have warmer-than-normal temperatures in the Pacific all the way from the Gulf of Alaska down to the El Niño area," claims Redmond of WRCC.

While blobs of warm ocean water have occurred in the Pacific before, experts insist these are some of the biggest in the last 50 years. Many meteorologists and climatologists strongly suspect there is a link between the blob and the dry winters of 2013-2014 and 2014-2015.

An intriguing question is emerging: How will the blob and El Niño get along this winter? How will their interaction influence the coming winter? "They could accentuate each other or subtract from each other. They could multiply each other or they might cancel each other. The jury is out," says Redmond.