What is a super El Niño? Could it end Colorado’s drought?

Hype around the potential of a rare super El Niño, and a possibly record-breaking one at that, gives hope there may be an end to Colorado’s historic drought conditions in sight.

With that hope should come a level of caution. After all, we are talking about long-range weather forecasting, which isn’t an exact science. Still, if Pacific Ocean water temperatures continue to trend warmer the way models are showing, we could see a record super El Niño.

But what does that mean and how might it impact weather in Fort Collins, Colorado and around the U.S.?

First, an explainer on what El Niño/Southern Oscillation is and how it impacts weather globally

The National Weather Service’s Climate Prediction Center tracks the El Niño/Southern Oscillation (ENSO).

ENSO is the natural recurring climate pattern resulting in fluctuating water surface temperature and air pressure along the central and eastern equatorial Pacific Ocean that influences global weather patterns, including a shift of the jet stream and storm tracks.

That water temperature oscillates between three phases: El Niño, above-average temperature of the equatorial Pacific Ocean; La Niña, below-average temperature; and neutral, no significant difference.

El Niño conditions typically result in cooler and wetter conditions for the southern U.S. in fall and winter, as the Pacific jet stream mainly tracks south, creating an amplified storm track. Conversely, the northern U.S. typically sees warmer and drier conditions in fall and winter.

Impacts in Fort Collins and Colorado, being in the center of the U.S., are not as pronounced but super El Niño years have produced bountiful snow and overall above-average precipitation. More on that below.

Here is the potential for when a super El Niño might form

Models are showing a growing trend of an unusual warming of sea surface temperatures across the central and eastern equatorial Pacific Ocean.

The stronger the El Niño, the greater potential there is for increased storm system frequency and threats of severe weather, including heavy rain, damaging thunderstorms and flooding, especially for the southern U.S.

Here are the percentages from the Climate Prediction Center, as of March 12:

• 55% chance of a transition from La Niña to neutral starting in April.
• 62% chance for neutral to transition into El Niño conditions June through August that are expected to last at least through the end of 2026.
• 33% chance El Niño conditions could become “strong” October through December, signified by equatorial Pacific Ocean water temperature 1.5 degrees Celsius above normal.

For El Niño conditions to form, the monthly ocean surface temperatures must reach 0.5 degrees Celsius above normal. For a super El Niño, the water temperature threshold is 2 degrees Celsius above normal.

Some models show a forecast of 2.5 degrees to 2.8 degrees Celsius above normal water temperature, which is around 4 to 5 degrees Fahrenheit. That would rival the 2015-16 record. 

How have super El Niños impacted Fort Collins, Colorado with rain, snow?

Peter Goble, assistant state climatologist at the Colorado Climate Center at Colorado State University, said there is a correlation between super El Niño conditions and above- to well-above-average rain and snow for Fort Collins and Colorado but cautioned the sample size is small.

There have been three super El Niños: 1982-83, 1997-98 and 2015-16, Goble said.

“I’m pretty confident in El Niño developing and that stacks the deck in our favor for more precipitation in Fort Collins, but when it comes to having super El Niños having a super impact, that’s stacking unknowns upon unknowns,” Goble said. “It’s a small enough sample not to get too excited, but it’s in really good company.”

Here are precipitation totals for Fort Collins in super El Niño years, according to Goble. The city averages 51.4 inches of snow and 15.88 inches of precipitation a year:

• 1982-83: 68 inches of snow and 24.22 inches of total precipitation.
• 1997-98: 55.3 inches of snow and 20.85 inches of precipitation, half or more of which fell on the western side of the city during the July 1997 flood.
• 2015-16: 72.8 inches of snow and 14.37 inches of total precipitation.

Goble said snowpack statewide during previous super El Niño years were 113% of normal in 1998 and 93% of normal in 2016. He said the state did not use the modern SNOTEL snowpack measuring gauges in 1983 but snowpack was 120% to 130% of normal.

Weather impacts in Colorado from regular El Niños are uncertain due to influences such as topography, distance from oceans and a variety of other variables, according to the Colorado Climate Center.

During El Niños, the strongest influence occurs in winter, when the entire state is likely to experience overall below-average temperatures.

There is far less predictability in regard to snow and rain totals compared to average despite some epic events, such as one of Fort Collins’ largest blizzards in 2003 and Fort Collins’ flood in 1997 occurring in El Niño years.

If a super El Niño arrives, how will it impact Colorado’s monsoon season, water storage?

Goble said the Climate Prediction Center outlook shows this summer’s monsoon “coming alive” in July through September, with an increase in moisture starting during the traditional monsoon months.

The monsoon is an annual weather event when a stream of moisture is pulled up from the Pacific, Gulf of California and Gulf of Mexico. It mostly impacts rainfall on the Western Slope but in some years those storms surge over the mountains to bring rain to the Front Range.

“As of right now, those dynamic models have been pretty bullish on a better than normal monsoon season with a bull’s-eye of moisture around the Four Corners area,” Goble said. “There will be a chance that bleeds into the Front Range.”

Historically low snowpack has already prompted water districts and municipalities to restrict water use. As of April 9, normally the peak snowpack in the state, snowpack was 22% of normal, according to the Natural Resources Conservation Service. The South Platte Basin, which serves Fort Collins and Boulder, was at 32% of normal.

The entire state is in some designation of drought with 95% in moderate to exceptional drought and much of the mountains experiencing extreme to exceptional drought conditions, according to the U.S. drought monitor map, as of April 9.

The low snowpack will stress the state’s reservoir water storage, which in central and northern Colorado is around 80% of normal for this year.

Goble said Lake Granby, the centerpiece of the Colorado-Big Thompson water delivery project that serves much of Northern Colorado, is in decent shape and has enough storage to sustain one bad snowpack year, but not two in a row.

He said there is experience of a low snowpack year being followed by abundant snowpack that refilled reservoirs in one year. Goble said while big rain years help reservoir storage, the vast majority of water storage comes from snowmelt.

“I hope we have a snowy season like 2018-19 and 2022-23,” Goble said. “Those years showed that one banner year can undo the damage of a low snowpack year. I’m cautiously optimistic that things will turn in our favor.”