Another La Niña Is Forming. What Does That Mean for Winter in Denver?

The days are getting shorter, the leaves are changing, and we’re starting to see some massive temperature swings. Those seasonal changes mean it isn’t too early to start thinking about winter—and how much snow might be headed our way through the colder months.

Early indications suggest that we will have a La Niña winter for the second consecutive year. While La Niña conditions are still forming, this winter’s version will likely be weaker than last year’s, which helped produce one of the snowiest seasons in Denver history. During previous years with weak La Niña conditions (see the dry 2017-18 winter), the Front Range has usually experienced average to below average snowfall.

The conditions for La Niña are determined by water temperatures near the equator, off the coast of South America. During what is known as El Niño, the waters in the Pacific become warmer than average and typically cause east winds to blow weaker than normal. La Niña occurs when water temperatures are colder than average and east winds blow much stronger. While those temperature swings only vary within a range of four degrees Celsius, they are enough to alter global weather patterns.

While the odds of a weak La Niña emerging this fall have been set at about 70 to 80 percent, there is still some limit to our understanding of what that means. Meteorologists started tracking data related to the El Niño Southern Oscillation (ENSO)—the aforementioned climate patterns in the Pacific Ocean near South America—in the 1960s, and there is some variance in what the data says about what impacts the equatorial waters of the Pacific Ocean have on Colorado’s winter.

While the evidence we do have suggests that a weak La Niña year will produce average to below average snowfall along the Front Range, there are also many factors that are not thousands of miles away that affect our local weather, including Colorado’s continued drought and downsloping winds from the Rocky Mountains, which cause warming temperatures and drying conditions.

Other predictors, however, suggest a similar forecast. The Climate Prediction Center expects Colorado will have a slightly warmer than average winter with normal precipitation across the state. In other words, you probably won’t be using all your PTO on powder days this winter.