The new December and winter outlook is out, and it is not straight forward. The attached Climate Prediction Center’s outlook shows a tilt of odds towards wetter than normal for much of western Colorado. With El Nino about to emerge in the eastern Pacific the seasonal Dec-Jan-Feb outlook shows the El Nino signature of wetter than normal across the southern tier of states. This does not match what we see in the short term with no major storms on the horizon for the next week or so. But towards the end of November there is a hint of storms coming in from off the southern California coast.
This also doesn’t match well what we have seen for previous seasons with emerging El Nino. El Nino years typically produce a wet fall, such as October thus year, and a wet spring, but a drier heart of winter. See second attachment.
What have recent El Nino winters produced in Colorado? There have been five El Nino winters this century.
2015-16, a strong El Nino, – above normal snowfall central and south Colorado, near normal north
2009-10, moderate El Nino, – above normal south below normal north
2006-07, moderate, – dry except snowy on the Front Range
2004-05, moderate, – above normal south below normal north
2002-03, moderate, – below normal west, above normal Front Range.
Further back in our El Nino history, 1994-95 was a snowy year. But very dry El Ninos occurred in 1976-77 1986-87, and 1965-66.
How much of our winter hinges on El Nino/La Nina? Studies by the CPC showed ENSO explains somewhere between 15-25% of a Colorado winter’s weather, see the third attachment. And remember that it only takes a few storms to make a snowy winter, or the absence of those storms for a dry winter.
Joe Ramey ~ Mountain Weather Master