How a La Nina could impact Colorado weather this year

It appears increasingly likely that La Nina conditions will develop in the central Pacific Ocean later this year, and that could have significant short- and long-term impacts on Colorado’s weather.

The opposite of El Nino, a La Nina means that sea-surface temperatures in the east-central Pacific Ocean are running cooler than average. In short, this creates a well-documented domino effect on global weather — including direct impacts on Colorado’s weather.

National Weather Service computer forecast models and official Climate Prediction Center prognostications are indicating an increased probability of cooler-than-average sea-surface temperatures in the centraleastern Pacific Ocean this fall and winter. Last week, the CPC increased the odds of a La Nina developing this winter up to 45% – and lowered the odds of an El Nino event to just 10 percent.

El Nino and La Nina, known as the ENSO cycle, tends to have a big (although varying) impact on weather, particularly during the winter months.

La Nina tends to bring in colder and wetter winter weather to the northern United States, often putting Colorado right on the border of those impacts. That’s because the polar jet stream tends to stay a bit further north during a La Nina winter, bringing in frequent waves of colder weather and snowfall.

Because of Colorado’s central continental location, though, ENSO impacts are highly variable, and they change dramatically from one side of the state to the other. In general, an El Nino winter tends to increase snow totals in southern Colorado, due to a more active subtropical jet stream during the winter.

But, with the growing prospect of a La Nina winter in mind, that could favor northern Colorado’s winter snow chances. In general, La Nina winter storm tracks tend to favor the Pacific Northwest, and that could increase odds for a snowier winter in northern parts of the state.

In the shorter term, though, ENSO conditions are expected to remain neutral, something that could increase probabilities of a more active Atlantic basin hurricane season, but that’s unlikely to have significant impacts on Colorado’s summer weather.

In the near term, the CPC summer outlook for Colorado generally leans warmer and drier than average.

With a possible La Nina on the horizon though, there are at least some hints that Colorado weather could see some big impacts from it, especially by this winter.