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 November 19, 2018 - El Niño-level SSTs were observed in the October average, and the subsurface waters also continued to be markedly warmer than average. However, the atmospheric variables showed mainly ENSO-neutral patterns. Only lower-level wind anomalies averaged weakly westerly in the eastern Pacific - a suggestion of El Niño. The official CPC/IRI outlook calls for an 80% chance of El Niño prevailing during winter, and a 55-60% chance of continuing into spring 2019. An El Niño watch is in effect. New forecasts of statistical and dynamical models collectively show continuing El Niño-level SSTs, most likely weak to moderate in strength, continuing through spring. Read More...


Potential Impacts

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

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. Despite these relationships, winter precipitation during every El Niño has been all over the board for Colorado, including wetter than average during the 1951-52 weak El Niño winter, and drier than average during the 1976-77 weak El Niño winter.

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 winter brings an increased risk of wet extremes and a decreased risk for dry extremes for the eastern plains. Western Colorado is more of a mixed bag, but based on the larger scale patterns, the southwestern corner is also probably at an increased risk of wet extremes. 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 Watch mean? - The El Niño and La Niña Alert System

Read the latest ENSO blog entry at Climate.gov - November 2018 ENSO Update: (Just a little bit of) history repeating
"During El Niño, warmer-than-average water in the east/central Pacific results in more rising air, clouds, and rain than normal in that region. This weakens the whole Walker circulation, meaning both the upper-level and lower-level winds are slower than normal..."