By Justin McHeffey
As we head further into the summer season we're expecting a shift in our climate pattern. The 2015–16 El Niño episode brought more moisture and cooler temperatures across the region. The current outlook shows a transition to La Niña conditions in the Pacific Ocean — a setup that could reverse our recent trend of above average snowfall.
After an unusually high snowfall year at most Colorado ski resorts, the El Niño projections from one year ago were correct. Many major and independent resorts measured 350–400 inches by the end of the ski season. The Climate Prediction Center is now forecasting a 75 percent chance of La Niña during fall and winter 2016–17. Typical La Niña episodes bring less moisture and warmer temperatures to Colorado. Looking at the past 10 years, we've recorded two moderate events and one weak La Niña. On the high end, Denver's snowfall was 32.5 inches below average during the 2010–11 episode.
Sea surface temperatures in the Pacific Ocean show a cooling trend along and east of the International Date Line. Observing water temperatures in this region is the primary method used to determine changing circulation patterns. Based on the past 66 years of data, it's uncommon to see a strong La Niña develop immediately after a strong El Niño. In only one instance — from the strong El Niño in 1972 to the strong La Niña of 1973 — was there evidence of both extremes happening back-to-back. The 2015–16 El Niño was among the top three strongest in recorded history.
From the middle of January through the end of May 2016, the eastern Pacific showed a decrease in water temperature. Since late May, temperatures have leveled off but remain cooler than average.
Long range forecasts are difficult to predict accurately, but if the water stays cooler than normal in the coming months, La Niña will influence our climate through the upcoming winter season. During La Niña events, the jet stream tends to favor the northern tier of the country, rather than the southwestern U.S., and is the main reason that Colorado usually measures less snow.
Although the statistical chances for heavy snowfall are lower during La Niña episodes, there have been exceptions. Copper, Arapahoe Basin, and Loveland all broke seasonal snowfall records during the 2011 La Niña cycle. Even though the climate guidance says we should expect less snow next winter, the forecast is always subject to change.
Justin McHeffey provides nightly reports from the Mobile Weather Lab. He travels Colorado in search of Mother Nature's most powerful and beautiful conditions. Like his Facebook page Meteorologist Justin McHeffey and follow him on Twitter @WeatherMcHeffey.
