No one likes a houseguest that overstays her welcome, and it seems La Niña has finally gotten the hint. La Niña, a weather pattern where the equatorial waters of the Pacific Ocean are cooler than normal, has stuck around for three whole years—rather than her usual nine to 12 months. And her prolonged stay has had profound effects in Colorado, including a seriously stubborn drought. But now that La Niña has packed her bags, it’s time to prepare for our next visitor: El Niño.

We’d forgive you if you forgot about our old friend El Niño; it’s been awhile since he’s made an appearance. But if you recall, he’s everything La Niña isn’t: During El Niño, the equatorial waters of the Pacific Ocean are warmer than normal, which tends to lead to snowier—or sometimes rainier—winters, particularly in the southern mountains of Colorado.

Below, we answered four of your burning questions about El Niño.

When will El Niño arrive?

Well, he’s already here. The National Oceanic and Atmospheric Administration (NOAA) announced the onset of El Niño conditions in the tropical Pacific Ocean on June 8, which will impact weather all across the world. But there’s no need to get frantic on the Front Range. This weather pattern typically only influences Colorado between September and February. We’ll ebb and flow through wet and dry patterns for the remainder of summer—like usual—until we reach fall. Then we should see wetter than normal conditions into the new year to February, when we can expect a slight drop-off in precip statewide.

A map of the typical winter impacts of El Niño. Photo courtesy of NOAA

How did we go from La Niña to El Niño so quickly?

For us ENSO amateurs who don’t spend our days studying the tropics, the switch likely flew under our radar. Considering the weather whiplash Colorado’s been giving us the last six months (like when we went from winter wonderland to sunny springtime in what felt like 24 hours), large-scale patterns can be difficult to spot.

Kyle Mozley, a National Weather Service meteorologist based in Pueblo, explains that the switch happened gradually, thanks to multiple meteorological events interacting: El Niño and something called the Madden Julian Oscillation (MJO).

The MJO is a large disturbance of rain, wind, and clouds that travels east across the globe every 40 to 60 days. The strength of the MJO can be altered by other recurring climate patterns, including La Niña. For the last three years, La Nina has made the MJO pretty weak, meaning fewer deluges of rain and snow. Remember when we went a whopping 222 days with no snow in 2021? But in late 2022, it rediscovered its oomph.

The MJO in December 2022 and the one in March 2023 produced heavy precipitation in western Colorado. “Ever since, each passing of the MJO has weakened the strength, and therefore impacts, of La Niña,” Mozley says. “Eventually, La Niña eroded in March, paving the way for El Niño to develop.”

Will El Niño impact monsoon season?

Colorado’s monsoon season usually begins in July and subsides by September—although we have had an unusually rainy June thanks to a rare flow of moisture blowing in from the Gulf of Mexico. But will El Niño spell a soggier summer? Mozley says that’s unlikely. “The monsoon is a completely different ball game with minimal influence from El Niño.” If Coloradans do get more rain the next few months, El Niño won’t solely be to blame. Remember: We won’t notice the effects of El Niño until fall, when we’ll probably want to bundle up for the extra snowfall predicted.

Was La Niña really that dramatic?

For the most part, yes. “Looking back at the weather across the state, the first two La Niña years were both on the drier side,” Mozley says. “The peaks in precipitation were mostly below average, and then fell off sharply during the spring months. This year has been very different. The continued periods of snow have us being above normal, especially for areas out west [in Colorado]. Again, this is likely due to the MJO events that occurred over the winter months and continue to impact Colorado.”

Colorado won’t be impacted much by the strengthening El Niño until the upcoming fall and winter months. But then, prepare for what’s predicted to be a white—and abnormally wet—holiday season. Given our drawn-out drought, this is one houseguest who’s welcome to stay as long as he likes.

Andy Stein
Andy Stein
Andy Stein is a freelance meteorologist with experience working on both local and national television.