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Are we in an El Niño or La Niña year? Here's the difference

Posted on by Vanessa
Are we in an El Niño or La Niña year? Here's the difference

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Meteorologists are watching a strong weather event that could keep Arizona unusually warm and dry throughout the winter.

The National Weather Service has issued a La Niña warning, with a 60% chance of La Niña conditions developing through November. If it does occur, climatologists predict La Niña will last from January to March.

“We are supporting the emergence of La Niña conditions,” said Jon Gottschalck, chief of the National Oceanic and Atmospheric Administration’s operational forecast division.

While climatologists are confident that La Niña will occur in the next month or two, they cannot be sure.

“We are still a little away from these effects,” said Gottschalk. “We are still waiting for these conditions to officially develop in the ocean, and then the atmosphere will have to respond.”

Here's what you should know about the El Niño and La Niña patterns and how they affect Arizona's weather.

What is La Nina?

La Niña and its counterpart El Niño are climatological events that are part of a natural cycle called the El Niño-Southern Oscillation, or ENSO. It represents the relationship between ocean temperatures and atmospheric conditions originating from the Pacific Ocean.

During a La Niña event, the trade winds that blow from east to west near the equator intensify. Stronger winds are pushing warm water from the eastern Pacific into Asia and warming surface temperatures in the western Pacific. This shift is resulting in deep, cold water in the central and eastern Pacific.

Cool water drawn in from the ocean depths by the wind shift triggers a chain reaction of weather events. Once the atmosphere responds to changes in ocean temperature, areas such as Indonesia, the Philippines and northern Australia tend to experience more tropical rainfall.

During La Niña, the Pacific Ocean tends to have a weaker hurricane season, while the Atlantic Ocean has a busier season.

More: La Niña could turn Arizona's hot, dry summer into a warm, dry winter. What you should know

What does a La Niña winter look like? Is La Niña warm or cold?

La Niña influences weather around the world, but the effects vary by region.

The Southwest, central Rocky Mountains, Gulf Coast, and East Coast tend to have warmer, drier winters.

In the Pacific Northwest, New England and the Great Lakes regions, La Niña typically causes wetter winters.

What would La Niña mean for Arizona weather?

If La Niña conditions occur, Arizona will likely experience a drier and warmer winter, but scientists expect this to be a weaker event.

“Typically, temperatures in the Southwest with La Niña are generally warmer than normal early in the fall or winter,” he said. “During La Niña events, there is a fairly strong signal of below-average precipitation in the Southwest and Southern Plains.”

NOAA recently lowered its La Niña probability from 71% to 60% and expects extremely dry and warm conditions will not occur in the Southwest.

“La Niña forms quite slowly, and the slower it forms, the less time it has to actually peak,” said Michael Crimmins, a climatologist at the University of Arizona.

Although it likely won't be the driest or hottest winter on record, La Niña could still have a negative impact on Arizona.

After an unusually dry monsoon, Arizona soils and vegetation are drier. Below-average winter precipitation could further strain water supplies and worsen next year's wildfire season.

“We are perpetually in a period of drought, and an impending La Niña event does not mean relief,” Crimmins said. “It most likely means further deterioration or a slide into a short-term drought.”

More: Can meteorologists predict the weather for 90 days? Why long-term prospects are so complicated

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