Matt Makens

Earlier this year, we were still in the grip of La Niña, but from April through
August, we saw a transition toward El Niño. 

El Niño began to develop in the spring and by summer had a more powerful grip on
the atmosphere. There are multiple ways of measuring how strong the grip is,
whether that be in the atmosphere, ocean or a combination of those two.

The atmosphere's behavior is shown here, by one such metric called the SOI,
where positive values are La Niña characteristics and negative values for El
Niño.

That sharply negative trend in the most recent period is the developing El Niño.

Most forecasts you will see for El Niño are from one specific area of the
Pacific Ocean. Since that is most commonly what you will see, I will use that to
give you some perspective on the El Niño of 2023-2024.

I can show you all El Niño events since 1980 on one graph. Each individual line
represents the ocean temperature anomaly in that specific region I just
mentioned. You can see multiple years surrounding 2023’s line through this
summer.

We can see a lot of variation between those lines – and that’s the point; no two
El Niño events will be identical. 

Based on previous similar years, that red line representing 2023 will likely
peak later this year. Once we cross into 2024, history shows a trend that will
take us back out of an El Niño and into neutral territory. 

Our current trajectory matches history, toward a moderate to one of the stronger
events since 1980 for the winter.

Considering this, what have these most similar years done to the country’s
temperature and precipitation patterns? Let us look. 

Let us start with temperatures. Moderate to strong El Niño events will lean
toward warmer than normal temperatures across the northern states, especially
the Pacific Northwest, Northern Rockies, and Northern Plains. Cooler than
average temperatures across the southern states, especially the Southwest and
Southern Plains.

Precipitation from those most similar El Niños favors the Southern U.S., Central
Plains, and limited pockets of the Pacific Northwest. Again, this map represents
the average of similar events.

When do we see the impacts, now that we see generally where we are headed
throughout the winter (I’m using the word winter loosely here, meaning the cold
season of November through April rather than just the technical three-month
winter season)?

El Niño events evolve as the season progresses, just like the atmosphere always
ebbs and flows. El Niño’s impact typically begins first for the Northwest and
Southeast, then shifts toward the central states and finally toward the
Southwest and Great Lakes by the second half of the season. I created the
previous map to give you a bit of a sense of when your region will see the
bigger changes.

How close to these historic averages will we be this year? Time will tell,
obviously, but we also need to get through October to see the ultimate strength
of this El Niño event.

Insiders: El Niño and the extended outlook