The National Weather Service declared the winter under weak La Niña influence

La Niña has officially arrived, but due to its late onset, forecasters are expecting a weaker than normal climatological event that will not impact the weather as much as in previous years.

The National Weather Service said La Niña conditions were in place Thursday morning, with a 59% chance they will last from February to April.

However, it is almost as likely that a neutral pattern will emerge between March and May, with a 60% chance that meteorological conditions and ocean temperatures will return to normal.

La Niña winters tend to bring drier and warmer conditions to Arizona, but since sea surface temperatures rarely reach the La Niña threshold, this may not have as much of an effect.

“This appears to be more of a weaker La Niña pattern, so it will be fairly weak and short-lived,” said Isaac Smith, a meteorologist with the National Weather Service Phoenix. “It’s pretty borderline at this point and if we switch to neutral it won’t affect us too much.”

Here’s everything you need to know about La Niña and how climatological patterns affect Arizona:

Weathermaker:El Niño or La Niña? Here’s the difference and what it means for Arizona weather

What is La Niña?

La Niña and its counterpart El Niño are climatological events in a natural cycle called the El Niño-Southern Oscillation, or ENSO. These events represent the relationship between ocean temperatures and atmospheric conditions in the Pacific Ocean.

During a La Niña cycle, the trade winds that blow from east to west near the equator intensify. These winds push warm water from the eastern Pacific to Asia and warm surface temperatures in the western Pacific. This creates deep, cold waters in the central and eastern Pacific.

“If we see some cooling in a particular region based on sea surface temperatures in the Pacific, that suggests a La Niña pattern is forming,” Smith said.

Cooler ocean temperatures are triggering a chain reaction of weather events worldwide, affecting temperature and precipitation.

El Niño is the opposite condition, as the trade winds weaken or even reverse direction and ocean temperatures rise.

These patterns typically last nine to twelve months, but can last for years. Statistically, they typically occur every two to seven years, but there is no predictable schedule.

A third ENSO pattern, a neutral phase, occurs when trade winds and ocean temperatures are closer to normal and there are no weather extremes triggered by El Niño or La Niña.

Dryness:Why is it so dry this winter? No rain or snow is expected for Phoenix and Flagstaff

How will La Niña affect Arizona?

La Niña affects different regions of the world differently, but tends to produce warmer, drier winters in Arizona.

With weeks of above-average temperatures and no measurable precipitation since August 22, this winter definitely appears to be under the influence of a La Niña pattern, at least in part.

“Although La Niña was just officially declared, the atmosphere had been looking like a La Niña event for some time,” said Arizona State Climatologist Erinanne Saffell.

“Arizona’s snowpack is at 18% of average, similar to the amount at this point in 2021, 2018, 2006 and 2000, all La Niña winters that ended as dry winters for Arizona,” she added.

But other factors also play a role in Arizona’s winter weather.

Long-term and short-term droughts, high and low pressure systems in the atmosphere, and increased temperatures due to global warming all play a role in weather that can mimic the common symptoms of a La Niña cycle.

During the La Niña period, warmer and drier winters are statistically common in the Southwest, but these conditions cannot be guaranteed.

“Just because we have a La Niña pattern doesn’t mean these conditions are always the case,” Smith added. “A few years ago we had a La Niña pattern and we had a pretty wet and snowy winter here in Arizona.”

How will neutral conditions affect Arizona?

Sea surface anomalies in the Pacific must fall below a threshold of -0.5 degrees Celsius to be classified as a La Niña event.

This week, the National Weather Service reported anomalies of -0.7 degrees and -0.6 degrees in certain regions, just exceeding the limit.

“It has to reach a certain threshold to be considered La Niña, and if it doesn’t reach that, it’s considered ENSO neutral,” Smith said.

However, with a weak event, meteorologists expect conditions to return to neutral in the next few months.

“Right now we’re continuing this streak of days without rain,” Smith said. “We are currently in the top three of the longest stretches without rain. So hopefully it can rain at some point.”

The National Weather Service declared the winter under weak La Niña influence

ByAmelia Journalton

By Amelia Journalton

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