With weak to moderate El Nino conditions expected for the Winter of 2009-2010, I was curious as to what impacts it might have on seasonal snowfall totals across Colorado. I did a quick study by looking at annual snowfall totals for Greeley, Evergreen, and Breckenridge, CO for the winter seasons of 1972-73 through 2008-09 during La Nina, ENSO-neutral, and El Nino years. I picked each of these locations to represent the Colorado Front Range Plains, Foothills, and Mountains respectively.
I classified each winter season (Oct-Mar) as La Nina, ENSO-neutral, or El Nino by calculating the average Oceanic Nino Index (ONI) for each season… and it’s considered:
- La Nina when ONI was less than or equal to -0.5
- ENSO-neutral when ONI was between -0.5 and 0.5
- El Nino when ONI was greater than or equal to 0.5
Then I calculated the average annual snowfall during each ENSO cycle and found for:
- Greeley during La Nina years the average snowfall was 42″, neutral years was 40″, and El Nino years was 40″ (average annual 41″)
- Evergreen during La Nina years was 77″, neutral years was 71″, and El Nino years was 96″ (average annual 81″)
- Breckenridge during La Nina years was 179″, neutral years was 157″, and El Nino years was 167″ (average annual 169″)
Over the Colorado Plains, well Greeley anyways, there’s really no signal that would suggest that El Nino conditions affect snowfall totals with the average annual snowfall being 41″ for all years and 40″ during El Nino years. For the Colorado Front Range Foothills, Evergreen sees an average of 15″ more snow during El Nino conditions as compared to normal. In the central Colorado mountains, Breckenridge sees an average of 169″ during El Nino years, which is 2″ less than normal.
So, for those who live on the Eastern Colorado Plains, more than likely, this up coming El Nino will not have any impacts on seasonal snowfall totals. Those living in the Foothills will have a better chance for seeing more snow than normal. For folks in the central mountain locations El Nino will more than likely have little to no impact on snowfall totals (maybe a couple inches less than normal).