Answered by Timothy Axford – Meteorologist – National Weather Service – Pocatello
Great question! Meteorologists get asked this a lot. As the days shorten and we start looking towards the winter season, everyone wants to know whether it will be several months of cold and snowy or mild and dry. Meteorologists and Climatologists (someone who studies the climate patterns) often use signals such as the El Nino Southern Oscillation Cycle (ENSO) to understand how individual seasons may take shape. So, to talk about what we’re looking at this winter, and how the La Nina may affect it, we need to first understand the basics of what the broad climate pattern ENSO is.
The El Nino Southern Oscillation is a recurring climate pattern across the tropical Pacific where changes in water temperature lead to changes in the position of the jet stream and downstream weather patterns. That’s how something hundreds of miles away can affect us here in eastern Idaho! This natural cycle can shift from warm phases (El Nino) to cool phases (La Nina) every two to seven years. The image to the right shows the changes in sea surface temperatures during these two phases.
Now that we have a better understanding of what ENSO is and we know that we’re in a La Nina year, what exactly will that mean for us? Below is a picture of a “typical” La Nina pattern in which the jet stream sets up to bring rounds of colder and wetter weather into the Pacific Northwest that can extend into the Intermountain West where we’re located.
Of the last 60 winters, 20 of those are considered to be La Ninas. Out of those 20 seasons, 15 of them were wetter or snowier than an average year. But we want to caution, there is a lot of variability year to year and season to season. 5 of the last 20 La Nina winters were drier than average. While the entire winter may not be cold and snowy throughout, we can say with some confidence that La Nina winters favor more rounds of cold and snowy weather. It may be time to get those sleds ready!