ENSO, or El Niño Southern Oscillation, is a climate pattern based on the water temperatures of the equatorial Pacific Ocean. There are three different phases of ENSO; El Niño (warmer than average water temperatures, Neutral (average water temperatures) and La Niña (colder than average water temperatures).
Currently we are in a La Niña phase which is forecast to last through winter and into Spring of 2021 and just as you’d expect, that has implications of what our winter will look like here in Colorado. A fascinating aspect of meteorology is that weather can be affected by local influences such as the concrete in a city creating a ‘Urban Heat Island’ effect which is what tends to keep Denver warmer at times than surrounding areas. Other times it’s larger features like the continental divide that forces air upwards and creates a cloud that hangs over the city throughout the day. Sometimes it’s extremely large features like water temperatures in the equatorial Pacific that can alter the path of the Jet Stream, or fast-flowing atmospheric river of winds, that steer storms towards and away from us.
And that is exactly what we are going to be watching for the upcoming winter. In a typical La Niña year, the Jet Stream tends to flow down from the Pacific Northwest area, through the northeast corner of Colorado and into the Tennessee Valley before curving up and over the northeastern United States. The Jet Stream is largely why storms move from west to east so we can infer that this winter, most storms will track near and to the north of us.
All La Niña years are different and there is no direct correlation on how a La Niña setup impacts Colorado but there are generalizations that can be made. In a normal La Niña setup, Southern Colorado typically ends up seeing a drier than normal winter, elsewhere it’s a little harder to pin down specifics.
For the Front Range, the best way to forecast this upcoming winter is to look at previous winters where La Niña was present. That brings us to the winter of 2017/18. Denver averages about 56” of snow per season, during the 2017/18 winter, Denver picked up 25.7” of snow. The 5th lowest total in the city’s history. The prior winter, 2016/17, was also a La Niña year and Denver totaled 21.8” of snow for that season. The second lowest snowfall total in the city’s history. 18 of the last 22 La Niña winters have produced less than average snow for the Mile-High city.
This doesn’t mean that we are guaranteed to have a below average snowfall season, but the numbers are rather strong. In regard to the High Country snowpack, there is no concrete evidence showing how that is impacted but the La Niña wind direction and topographical forcing tends to create good snow setups for the Central and Northern mountains at times.
Now, if you’re a snow lover, not all hope is lost! The Farmer’s Almanac says that Colorado will get more than enough snow. It states that we should be on alert for a big November storm and a string of storms in February. The Farmer’s Almanac started back in 1818 and makes predications based on their original weather prognosticator which took into account sunspot activity, planetary positions and the effect that the moon has on Earth. While at times the Farmer’s Almanac may end up being correct, their forecasts are more of a guess than an actual meteorological forecast. Personally, I’d love to believe the current Farmer’s forecast because I love snow, but my tingly weather senses are urging me otherwise.
Regardless of what happens, we desperately need any kind of wet weather to help our current and expanding drought. Winter rains and snows are usually good drought-busters but this year, timing may not be on our side.