ENSO and Colorado

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...

El Niño Phase
La Niña Phase

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...

Typical Winter El Niño Impacts
Typical Winter La Niña Impacts

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.

El Niño & Temperature
November - March
May - September

La Niña & Temperature
November - March
May - September

El Niño & Precipitation
November - March
May - September

La Niña & Precipitation
November - March
May - September

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.

Current ENSO Conditions

Current sea surface temperature anomalies in the tropical Pacific Ocean

CPC/IRI PUBLISHED February 14, 2019 - SST in the tropical Pacific cooled to a borderline to weak El Niño level in January and early February, while subsurface waters continued to be warmer than average. However, some atmospheric patterns of El Niño that had been lacking, finally developed in late January and February. Collective forecasts of models show weak El Niño-level SSTs into summer. The official CPC/IRI outlook, now carrying an El Niño advisory, calls for a 65% chance of El Niño prevailing during Feb-Apr, down to 50% for Apr-Jun. Read More...


Potential Impacts

By now, most Coloradans have heard the term "El Niño" thrown around about this winter. We know that it's likely to continue through the winter and into the spring. So many people are now wondering, "what does this mean for the rest of winter and spring? Will we get more snow or less snow?"

Anybody who's lived in Colorado for more than 5 minutes knows the weather can be sporadic. While predicting the weather out 5 days can be a challenging hurdle, predicting the climate several months out can be a monumental task that doesn't always pan out. An El Niño does give us some helpful information that can help steer us in a direction, but the relationship between El Niño and Colorado winters is not always a perfect one.

The eastern half of the state tends to receive greater than average snowfall during an El Niño, and it's also common for the northern mountains and Yampa valley to see less than average snow in an El Niño winter. While this pattern has panned out for the mountains east of the Continental Divide and southeast CO this winter, thankfully the pattern has lined up for the northern mountains and the Yampa valley, which have seen plenty of snow! This could be due to the fact that we are currently in a weak El Niño that has had limited response in the atmosphere.

NOAA's Physical Sciences Division at the Earth Systems Research Laboratory offers a pretty cool ENSO Climate Risk Tool that shows what regions are at an increased or decreased risk of climate extremes during an El Niño or La Niña at different times of the year. For Colorado, an El Niño spring brings an increased risk of wet extremes and a decreased risk for dry extremes for the entire state. This could be good news for drought relief, and also means there is a lower chance of drought intensifying in the next 6 months for areas currently in drought.


What does an El Niño Advisory mean? - The El Niño and La Niña Alert System

Read the latest ENSO blog entry at Climate.gov - February 2019 ENSO Update: El Niño conditions are here
"What's new over the past month is that we're seeing signs of El Niño-related changes in the atmosphere, with increased clouds and rain in the central Pacific indicating a weaker Walker circulation...."