It is September in the Colorado Front Range foothills, and with the cold season just a few months away, the perennial question has to be asked , “How much snow will Nederland receive this winter?” This is particularly true for skiers. When making seasonal forecasts such as these, meteorologists rely on a separate set of techniques and data than those used for making short-term, day-to-day forecasts. Annual to decadal changes in ocean temperature patterns can influence atmospheric circulations around the world, and weather forecasters closely examine these when making winter season forecasts. Why? Many decades of data have shown a correlation between these oceanic temperature oscillations and how severe winters are – at least in certain parts of our country.
The El Nino Southern Oscillation (ENSO) is probably the best known of the periodic departures from normal ocean temperatures. It resides in the equatorial Pacific Ocean and strong warm phases (El Nino) and cold phases (La Nina) have been shown to greatly influence the winter storm track across the United States. However, ENSO is not the only kid on the block. Others include the Pacific Decadal Oscillation (PDO), Arctic Oscillation (AO), North Atlantic Oscillation (NAO), and the Madden-Julian Oscillation (MJO). That’s just to name a few, and the combination of all these influences our weather is sometimes unpredictable ways. It is complicated to forecast these ocean temperature patterns and even more so to base long range weather forecasts on them.
The National Oceanic and Atmospheric Administration (NOAA) and the Farmer’s Almanac each produce winter outlooks and they do so using markedly different approaches (although the Farmer’s Almanac forecast is usually more entertaining to read). However, in the interest of keeping things simple, my outlook will simply be based on analogous winters here in Nederland which had a similar strength El Ninos or La Ninas.
Last winter featured the lowest seasonal snowfall (110.1 inches) I have observed in the 8 years we have lived in Nederland. It was also highlighted by a strong La Nina (cold phase) episode. Another low snow year in my records was the winter of 2010-2011 when I measured only 114.5 inches of snow. That winter was also dominated by a strong La Nina. Conversely, the strong El Nino winter of 2016 brought us 193 inches of snow for the season, the most I have ever observed. Moderate phases of La Nina and El Nino tend to bring closer to normal snowfall – around 153 inches. Considering that the Climate Prediction Center is forecasting a weak to moderate El Nino event this winter, a forecast of normal to slightly above normal snowfall for Nederland and the nearby foothills communities seems logical. El Nino does bring an increased chance of strong upslope snowstorms in the Fall and Spring, but temperatures tend to be slightly warmer than normal. Also, El Nino winters tend to be less windy.
To summarize, I expect:
- Seasonal snowfall to be in the 140-160 inch range with a few decent storms in the Fall and or Spring
- Temperatures to be near to slightly above normal
- Episodes of Chinook winds to be less frequent than last winter (amen)
To see the monthly average temperatures and precipitation for Nederland, visit: http://www.indianpeaksweather.net/nederland-climatology/
And remember, long range forecasts are always a bit of a crapshoot. One big storm can skew the overall data. Sometimes you are better off counting the dark and tan bands on a wooly bear caterpillar.