A primer for the upcoming winter from Joe Ramey, former NWS forecaster

Dear CPR,

Colorado Matters is a great show I try to listen to everyday. Thank you.

I am a retired NWS forecaster from the Grand Junction office, and was the Climate services focal point from 1999-2016. So I have spent some time trying to resolve Colorado climate patterns, but from the West Slope perspective.

On this Monday’s show, Mike Nelson talked about the winter outlook. I have written before about Mike’s seasonal outlook comments. He still has some inaccurate information for all of Colorado. And it seems Mike has a Front Range bias.

First, ENSO (El Nino/La Nina) has a complex impact on Colorado. 

La Nina winters favor much of the Colorado mountains with snowfall, as far south as Telluride. Crested Butte has a good snow response to La Nina. That snow response increases to the north. La Nina does not favor the Front Range or the southern portion of the San Juan mountains (and further south into NM-AZ). La Ninas are good news for the northern and central mountains including the headwaters of the Colorado, Arkansas, South & North Platte, and Yampa rivers. Therefore La Nina winters most often provide the best results for Colorado water use.

El Nino winters tend to have positive snow impacts as far north as the Highway 50 corridor. El Ninos are often good news news for the southern mountains, including the headwaters of the Rio Grande and Animas rivers. El Nino winters definitely favor the Front Range.

Extreme events.  La Nina winters tend to be the most stable ENSO pattern, with fewer extremely dry events. Both El Nino and ENSO Neutral winters show greater tendency for extreme events.

ENSO winter patterns. Colorado has a bimodal precipitation distribution with a wet fall and a secondary wet spring. El Nino tends to enhance this bimodal pattern bringing heavier rain in the fall and spring. La Nina, on the other hand, tends to diminish the fall and spring wet periods and enhance snowfall in the heart of winter. In monthly climate data, La Nina Januarys stand out as a snowy period.

Finally, ENSO only explains some 15-25% of Colorado’s winter weather. That leaves a lot to the impacts of random winter storms, but ENSO remains our best winter-outlook tool.

Thank you for letting me respond to the winter outlook portion of your show.

Joe Ramey