aecifo

New forecasts indicate La Niña conditions could be weaker later

Umito November 15, 2024

The National Weather Service has expanded its La Niña Watchnow predicting a weak, short event expected to emerge within the next couple of months.

La Niña conditions can lead to warm, dry winters in the Southwest, and weather services initially predicted such a cycle would emerge between September and November. She has now lowered her estimate to a 57% chance by the end of the year.

“It’s difficult to predict exactly what might happen in the event of a later start to a weaker La Niña, but statistically we could expect an overall drier January to March,” Erinanne Saffell said. , Arizona State Climatologist.

While ocean conditions reflect a brewing La Niña event, sea surface temperatures are generally near average and have not yet reached the La Niña threshold.

Here’s the latest on this year’s La Niña watch:

What is La Niña?

La Niña and its counterpart El Niño are climatological conditions that are part of a natural cycle called the El Niño-Southern Oscillation, or ENSO. The cycle represents the link between ocean temperatures and atmospheric conditions that occur in the Pacific Ocean.

ENSO has three phases: La Niña, El Niño and a neutral phase.

In La Niña conditions, the trade winds that blow from east to west near the equator intensify. Winds push warm waters from the eastern Pacific toward Asia, warming surface temperatures in the western Pacific. This change causes deep, cold waters in the central and eastern Pacific.

This sets off a chain reaction of weather events. Once the atmosphere responds to ocean temperature changes, more tropical rain tends to fall in Asia and Australia. This moves jet streams across the Pacific and North America, affecting weather patterns across the continent.

The Atlantic Ocean tends to experience a busier hurricane season, while the Pacific experiences a milder season.

El Niño is the opposite: trade winds weaken or even reverse completely, increasing ocean temperatures. Warmer waters send more moisture and energy into the atmosphere, triggering wetter conditions in many areas and amplifying the Pacific hurricane season.

The third ENSO pattern, the neutral phase, tends to produce temperatures closer to the trade wind and ocean average, without extremes triggered by La Niña or El Niño. Sea surface temperatures are currently near average, meaning ENSO neutral conditions continue for the time being.

What is the threshold for a La Niña event?

Climatologists monitor sea surface temperatures in the central and eastern equatorial Pacific to predict ENSO events. For a La Niña, they look for below-average sea surface temperatures.

The official threshold is 0.5 degrees Celsius below normal, or 0.9 degrees Fahrenheit.

As of November 14, the latest temperature change from normal in the Pacific was between 0.2 and minus 0.3 degrees Celsius below normal, below the threshold.

“La Niña forms quite slowly, and the slower it forms, the less time it has to peak,” Michael Crimmins, a climatologist at the University of Arizona, said in an October interview. “Historically, these events have given us mixed conditions for the Southwest. »

What does a La Niña winter look like?

With La Niña conditions developing slowly, climatologists are expecting a weak event.

La Niña affects regions differently. While the Southwest, Central Rockies, Gulf Coast, and East Coast tend to experience drier and warmer winters, the Pacific Northwest, New England, and Great Lakes typically experience winters more humid.

Even with a mild La Niña, Arizona will likely experience below average winter precipitation.

“That doesn’t mean we won’t have any precipitation, but it does mean that winter precipitation could be below average overall from January to March,” Saffell said.

“Arizona has been fortunate the last two winters with above-average precipitation, but unfortunately Arizona doesn’t often have three wet winters in a row,” she added. “The last time this happened was in 1991, 1992 and 1993.”

Hayleigh Evans writes about severe weather and related topics for The Arizona Republic and azcentral.com. Send him story tips to [email protected].