Indicators point to a wetter-than-normal winter in Northern Arizona

Not many of us will ever go to the central equatorial Pacific. But how it feels out there in Nino 3.4 dramatically affects the amount of moisture we can have during the winter in the Southwest.

Experts say we won't know the full story until it's over each season, but there are signs already that we are going to have a strong, even Super El Nino and a wet winter.

The Ocean Nino Index

Conditions of an El Nino, which can range from intervals of 2 to 7 years, were first recognized in the 1600s in South America, because the change affected fishing conditions west of Peru around Christmas time and was named after the Christ child; El Nino for the wet period and La Nina for the drier period.

The reason for the change was not fully understood until the 1950s.

Chief Meteorologist at the Flagstaff Weather Office, Brian Klimowski, says the Pacific trade winds and the amount of difference in average sea surface water temperature at the equator are key players in the El Nino phenomenon.

Typically warm air is blown from east to west across the Pacific and brings tropical rains to Asia and Australia. During an El Nino year, warm winds weaken, rise and storms develop over the Eastern Pacific instead, affecting the Western U.S. and South America but leaving the Western Pacific dry.

A very strong El Nino is now in play. One indicator is the difference in barometric pressure between Australia and Tahiti. Another indicator is the very high difference in sea surface temperatures measured on the equator in the Pacific. Dozens of bouys mounted along the equator in the Pacific sample the sea surface temperature and broadcast it to computers in the United States and elsewhere.

All of these El Nino conditions can become active when there is a difference of +.5 degrees Centigrade (an increase of about 33 degrees Fahrenheit), from normal of the sea surface temperatures.

Anything above 2 degrees Centigrade averaged over four weeks is considered a Super El Nino indicator. The strongest El Nino on record, recorded an ONI factor of +2.3C in 1997-98, when California received double its normal rainfall, Flagstaff received 35 inches more snow than average and Prescott doubled its amount of snowfall.

The 2015-2016 ONI index is already at 2.3 Centigrade.

Such conditions have diverse affects depending upon where you stand on the globe. In the American Southwest and California, we typically see storms, flooding and mudslides. States in the northern United States tend to be drier and warmer than usual. Gulf States are cool and wet.

On the other hand, South Africa is affected by drought. Australia sees drought, forest fires and crop failures. People near the equator in Pacific South America see flooding. Those in the Atlantic see fewer hurricanes.

"You can't really look at a storm and say that is because of the strong El Nino, but you are going to see a change in a pattern over a season and see seasonal precipitation totals affected," said Andy Taylor, science and operations officer at the Flagstaff Weather Bureau.

In the Verde Valley, we typically see a long dry period between the monsoon season and the winter storms, but there was no break this year.

"One characteristic of a strong El Nino year is increased tropical activity in the Eastern Pacific; more hurricanes and tropical storms off the coast of Mexico. We have certainly seen those this year," said Taylor.

"We also have seen a lot of moisture surges from late summer into the fall continuing into September and October."

"Talking specifically about Flagstaff, we have experienced six or seven strong El Ninos in the last 50-60 years. Strong El Nino events have ranged from the winter season of 1957-58 when we had only 71.5 inches of snow measured, well below our average of about 100 inches. But, in the winter of 1972-73, another strong El Nino year, we experienced 210 inches of snowfall, twice our average."

"When you take a composite of all the strong El Ninos we have experienced in the last few decades, and look at all the variability. When you average all those together, we tend to observe above-normal precipitation in Northern Arizona during a strong El Nino year. In the higher elevation where we have snowfall the snowfall there is above-average. However, it is not guarantee, but it is the tendency, and we need to be prepared for that."

"Like snow at the higher elevations, during a strong El Nino year, more rain can be expected at lower elevations in Arizona. So there is a greater tendency for flooding events along the Verde for example, if we get long duration precipitation. At the higher elevation, we sometime get rain-on-snow events, where we get a lot of rain on top of existing snow and it all runs off. An event like that happened in early March last year in Oak Creek."

Those events can happen but are more likely to happen in a strong El Nino year. Still, nothing is guaranteed. One of those rain on snow flooding events occurred in February 1993, with a 500-year flood on the Verde River, but Taylor said -- ironically -- 1993 was not a strong El Nino year.

The bottom line, said Taylor, is "more precipitation than average and a higher frequency of precipitation events during a strong El Nino year than in a normal year."

"While a major factor and the one we know the most about, there are also other factors in addition to the El Nino and other climate oscillations which can have an effect on Southwestern weather," he says.

So far this winter

To date this year, 11.2 inches of snow has fallen at the Flagstaff airport. According to the Flagstaff NWS Office, that is well above the 4.2 inches of snow that normally falls from Oct. 1 to Nov. 12.

So far, Prescott has recorded .3 inches of snow; normally they see one-tenth of an inch by Nov. 12.

"The important thing to remember is that we can only expect some relief in a best-case scenario with a strong El Niño event delivering abundant precipitation across the Southwest over the winter season. Current drought conditions have accumulated over years and cannot be erased by a single wet season.

"We can look back at drought indices around the time of the last strong El Niño event over the winter of 1997-1998," said Taylor.

But, whatever happens, El Nino is clearly here, according to a JPL expert.

William Patzert, climatologist for NASA's Jet Propulsion Laboratory, told the Los Angeles Times, "it's fair to say" that the current El Niño will be similar to the strongest two El Niños on record.

"If you look at the really big El Niños, that's '82-'83 and '97-'98, essentially the whole state of California got hosed, from north to south," Patzert told the LA Times.

"There's no longer a possibility that El Niño wimps out at this point. It's too big to fail."


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