Good odds for wet Arizona winter if El Niño remains strong

Good odds for wet Arizona winter if El Niño remains strong

University of Arizona Agricultural Meteorologist Paul Brown remains bullish about above average precipitation this winter in the Grand Canyon State if the current El Niño weather system continues to strengthen. In late July, Brown's odds were a 75-80 percent chance for a wet El Niño winter.

In late July, University of Arizona (UA) agricultural meteorologist Paul Brown remained bullish about above average precipitation chances this winter in the Grand Canyon State if the current El Niño weather system in the southern tropics continues to strengthen.

Brown is quick to note that a lot can change between now and then. He shared the optimistic weather forecast with alfalfa growers gathered for an UA-sponsored ‘Alfalfa Tent Talk’ held in Buckeye, Ariz.

“If the El Niño continues at its current pace or strengthens more, there is a 75-80 percent chance we could have above average precipitation this winter in Arizona,” Brown said.

If the El Niño fizzles out, as it has done over the last 5-6 years, Brown says “all bets are off.”

“Statistically, old climate science indicates that if El Niño is in place and strong by August then you have a really good chance of a wet winter. Right now, it is in the moderate phase and strengthening, and headed in the right direction.”

The last wet El Niño years in Arizona were 1998, 1993, and 1983.

The meteorologist added, “As of July, this year’s El Niño is projected to reach this same potential strength category.”

California drought relief?

Could a strong El Niño deliver a much needed moisture wallop in drought-stricken California?

A strong El Niño could deliver moisture to southern California, he says, but its impact on the Sierras is less certain.

According to Brown, “In the Sierras, El Niño is always a coin toss. The region can be real wet or real dry in an El Niño year.”

The El Niño could deliver additional moisture across the southern-most U.S. – from Arizona to Florida.

Wet winter punch

Brown is a realist, noting that the El Niño’s forecasted over the last 5-6 years turned out to be “duds,” or what he refers to as “El Foldo’s.”

This year’s system just might deliver a wet winter punch.  

“Right now, this El Niño is not a dud.”

Strange Arizona weather

Actually, Brown says Arizona’s weather began to change back in January, tied to the building El Niño. Temperatures from January through March were very warm yet and April was cool.

“May was about as cold as it can get in a low desert climate,” Brown said.

Rains occurred several times in May and June which is unheard of in the low desert in central Arizona. In addition, the Arizona summer monsoon (rainy) season normally begins in mid-July and started almost a month early this year.

The Arizona Meteorological Network (AZMET) station in Buckeye has recorded just seven June rains since it was installed 17 years ago. The station recorded two rains this June.

“This is about as strange of a growing season that we’ve had in a long time,” Brown told the alfalfa growers. “Some in the meteorology community believe the developing El Niño is already responsible for some of this year’s quirky weather conditions.”

He added, “This El Niño is strengthening. It has the potential to be a ‘big one.’”

If the strong El Niño holds its course, Brown encourages farmers to prepare for it this fall and winter.

“While a wet winter would be good to help address water supply concerns, it might not be good for farmers trying to manage alfalfa or cotton as they approach the late season and harvest.”

While a wet El Niño winter would help partially replenish surface water supplies in the state, it is doubtful that a single wet winter could offset the state’s drought, now in its 15th year.

Colorado River

Winter rains in Arizona would do little to improve the water situation in the Colorado River which supplies surface water in part to central Arizona farms. The water is pumped by the Central Arizona Project uphill from the river near Parker in La Paz County (northwestern Arizona) for delivery to farms and cities in central and south central Arizona, including the Phoenix and Tucson metropolitan areas.

Perhaps the larger question for surface water supplies in central Arizona is the chance for precipitation this fall and winter in the upper Colorado River Basin states, which in turn provide inflow and runoff into the Colorado River during the spring and early summer months for delivery to farms and urban areas.

“It looks like a wet bias for the Upper Basin States this winter, including in Colorado and Utah,” the meteorologist said.

Water flows from last winter’s snowfall in the Upper Basin into the Colorado River increased this spring and summer. Brown says an extra 3.5 million acre feet of water entered the Colorado River watershed in a six-week period; the result of late spring storms.

“That’s an amazing amount of water.”

About 70 percent of the total flow into the river occurs from April through July.

In fact, the probability of the U.S. Bureau of Reclamation declaring a shortage on the Colorado River has declined considerably for 2016 due to the spring storms.

“The Colorado River is looking much better water wise,” Brown said. “I think it’s a very positive development.”

The chances for a shortage declaration in 2017 remains possible if dry conditions redevelop in the Upper Basin.

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