The El Niño - Southern Oscillation (also known as ENSO) refers to a cyclical pattern observed in the tropical Pacific Ocean. There are three phases of ENSO - El Niño, La Niña, and Neutral. These phases relate to the ocean temperature anomalies that are occurring at any given time. If the ocean temperatures in the tropical Pacific are much warmer than average, then we are in an El Niño phase. If the temperatures are colder than average, we're in a La Niña. Climate.gov provides details on how exactly El Niño and La Niña conditions form. Read more...
The below graph shows how the ENSO phase has changed (or oscillated) over time. A couple of the strongest El Niño events include 1997 and 1982-83. Stronger La Niña events occurred in 1988 and 2011-2012. NOAA's Earth Systems Research Laboratory gives a nice discussion about past El Niño and La Niña events. Read more...
It's hard to believe, but the changing temperatures in the Pacific Ocean can impact weather all across the globe! Over the United States, for example, El Niño conditions can result in a wet winter for the southeast and a dry and warm winter in the Pacific Northwest. This happens because those changing ocean temperatures drive changes in atmospheric pressure, the jet stream, and overall weather patterns. The North Carolina State Climate Office has a great ENSO page that discusses ENSO impacts on the U.S. Read more...
For Colorado, the story is a little more uncertain. The complex topography of our state, our distant location from the oceans, and our sensitivity to a lot of other variables, means that ENSO competes with a lot of other forces in determining what our weather will be like! So, while ENSO does play a partial role in Colorado's climate, it's not always a guarantee.
Explore the links below to see how El Niño and La Niña impact temperature and precipitation anomalies around the United States.
For Colorado, you may notice that the strongest signal shows up in wintertime temperature anomalies during an El Niño, when the entire state is likely to experience overall below average temperatures. During a La Niña, the eastern plains are more likely to see above average temperatures in the winter and summer.
When looking at precipitation, there's even more uncertainty! The most dominant signal shows up during La Niña summers. At that time, much of Colorado has tended to experience slightly below average precipitation.
During an El Niño, no signal shows up over Colorado. This may be surprising for some of you. Thinking back to winters of the past during particularly strong El Niños (like 82-83 or 97-98) you may associate major Front Range blizzards with those seasons. And when you look at the years in the composite, you'll see that one of our largest blizzards (March 2003) also occurred during an El Niño year. But that signal is just not consistent enough to solely attribute it to ENSO or use it as a forecast for future El Niño winters.
CPC/IRI PUBLISHED May 19, 2021 - In mid-May, SSTs in the east-central Pacific are roughly 0.3 degree C below average, and the evolution of most key atmospheric variables are consistent with the end of La Niña conditions. A large majority of the model forecasts predict SSTs to remain near-normal through boreal summer. Similar to the new official CPC/IRI outlook issued earlier this month this objective outlooks calls for ENSO-neutral to persist through at least Jul-Aug-Sep, with greater uncertainty later in the year. A La Niña advisory is no longer in effect. Read More...
Summer 2021 Outlook: La Niña is dead, but that may not necessarily bode well
for Colorado's drought or the fire season ahead
Bouldercast, Ben Castellani, May 18, 2021
"...the most relevant analogs, those for an ENSO-Neutral summer following a La Niña winter and spring... the outlook is not as favorable for Colorado. A strong warm and dry signal is indicated across the entire state."
Read the latest ENSO blog entry at Climate.gov - May 2021 ENSO update: bye for now, La Niña!