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

FINAL La Niña Advisory Issued May 10, 2018
CPC/IRI PUBLISHED May 10, 2018 - In early May 2018, the east-central tropical Pacific waters warmed to ENSO-neutral levels. While most key atmospheric variables also indicated neutral conditions, the precipitation pattern and the upper level wind anomalies continued to show lingering weak La Niña conditions. The subsurface water temperature continued to be above-average. The official CPC/IRI outlook calls for neutral conditions through the September-November season, with a nearly 50% chance of El Niño development by year's end. The latest forecasts of statistical and dynamical models collectively call for weak El Niño development, but forecasters hedge due to low confidence at this time of year. Read More...

Outlook

Potential Impacts

As we move further into spring and closer to summer, the long-term predictability of weather and climate becomes increasingly challenging. As the days get longer and the air gets warmer, the Jet Stream pushes further to the north. Regardless of what phase of ENSO we're currently in, we see fewer large-scale storms track across the country. The dominant pattern of weather becomes convective (and local) storms. It's hard enough to predict when and where a specific storm will happen hours-to-days in advance. So, it's near impossible to predict the likelihood of events happening months in advance! As we shift into ENSO-neutral conditions, the sky's the limit for what sort of climate patterns may emerge over the next few months!

ENSO News

Read the latest ENSO blog entry at Climate.gov - May 2018 ENSO update: Thar she goes
"... The temperature of the water below the surface remained above-average, as the large area of warmer-than-average subsurface waters continued to move slowly to the east (a downwelling Kelvin wave). This warm area will continue to erode the remaining cooler surface waters over the next few months..."