What are El Niño and La Niña?

El Niño and La Niña are climate patterns in the Pacific Ocean that can affect weather worldwide [1]. During normal conditions trade winds blow west along the equator, taking warm water from South America to Asia. 

During El Niño trade winds weaken, and warm water is pushed back east toward the Americas. El Niño causes the northern part of North American to be warmer and drier than usual while the southern portion is wetter (Figure 1). 

a graphic showing el nino weather pattern over nation

Figure 1. Effects of El Niño on North America (Source: NOAA National Ocean Service)

La Niña is the opposite of El Niño. During La Niña trade winds strengthen, and even more warm water is pushed toward Asia. La Niña causes drier conditions in the southern US and heavy rains in the pacific northwest and Canada (Figure 2). Furthermore, winter temperatures are typically warmer than normal in the south and cooler than normal in the west. 


a graphic showing la Nina weather pattern over nation

Figure 2. Effects of La Niña on North America (Source: NOAA National Ocean Service)

Current Year and Effects on Iowa

Currently, El Niño is in effect, and it is expected to continue until at least March 2024 (Figure 3). The probabilities of El Niño fading away increase substantially beyond March and the most likely scenario is a return to a neutral ENSO through the summer of 2024 although the probabilities of La Nina developing by late summer are increasing which could lead to a colder, wetter harvest period in the coming year.

As outlined above, El Niño brings warmer than average winter temperatures to Iowa. According to KCCI Des Moines “Four of the last five strong El Niño winters in Des Moines have been considerably warm and at least somewhat less snowy than average” [3]. This is one reason this winter has been milder than normal so far this year and one reason to expect this trend to hold.

A graph of different colored barsDescription automatically generated

Figure 3. Official NOAA CPC ENSO Probabilities (Source: NOAA EL NIÑO/SOUTHERN OSCILLATION (ENSO)


While El Niño is a major climate pattern, there are other major climate patterns that influence Iowa weather as well. It is not a guarantee this winter will remain milder than usual. Remember, in Iowa, weather can change quickly. 



[1] What are El Nino and La Nina? (noaa.gov)

[2] Climate Prediction Center: ENSO Diagnostic Discussion (noaa.gov)

[3] Satre, Z (Nov 2023). El Niño returns: How that could affect this winter in Iowa. KCCI Des Moines   Here's what El Niño means for winter in Iowa (kcci.com)