El Niño predicted this winter; what does that mean for the Pacific Northwest?
Author: Paul Loikith, Climate Science Lab Director
Posted: August 29, 2018

The National Oceanic and Atmospheric Administration is forecasting a 60% chance that we will experience an El Niño event this fall with that probability increasing to 70% for this upcoming winter. 

Anomalies in sea surface temperature along the equator in the Pacific Ocean. (Courtesy/National Weather Service)

El Niño events often get a lot of attention here in the Pacific Northwest, but what does it tell us about the upcoming fall and winter in Portland? El Niño events increase the probability that a winter will be warmer than average by a small amount over much of the Pacific Northwest, but this does not mean that this winter will necessarily follow that rule, nor does it mean every day will be warmer than usual. What an El Niño almost certainly does mean is that the globally averaged temperature will be a little warmer the following year than if there weren’t El Niño conditions present.  

An El Niño event is the warm phase of an ongoing naturally occurring oscillation in ocean surface temperatures in the tropical Pacific. The cold phase is referred to as a La Niña. While El Niño and La Niña events are themselves confined to the tropical Pacific Ocean, these changes in ocean temperature have profound impacts on weather, even in places far removed from the tropical Pacific. Warm, moist air rises, carrying that heat and moisture into the atmosphere. When this large piece of ocean real estate changes temperature, the regions where air tends to rise change, which in turn has a ripple effect on the atmosphere. This causes some places to have increased probabilities of warmer or colder than average winter temperatures, and some places may be more likely to be wet and other dry.