Oregon Climate Variability
Climate in Oregon and the entire Pacific Northwest is influenced by two large-scale oscillations:
- the El Niño / Southern Oscillation (ENSO), and
- the Pacific Decadal Oscillation (PDO).
The El Niño / Southern Oscillation (ENSO) is the major source of year-to-year climate variability in Oregon. The Pacific Decadal Oscillation (PDO) is responsible for decade-to-decade variation. Though these two oscillations have a discernible effect on Pacific Northwest climate, a perfect forecast for the conditions of both ENSO and PDO explains only 30% of the variability in what is observed.
El Niño / Southern Oscillation
Although ENSO is centered off the coast of South America, it affects Oregon winters. When El Niño is in the warm phase, the odds tilt toward a warm and dry winter in the state. The cool phase of ENSO, La Niña, tends to cause a cool or wet winter.
For more about El Niño, including the current conditions, forecasts and information about episodes in the past, consult the ENSO page at the NOAA Earth System Research Laboratory.
Pacific Decadal Oscillation
The PDO affects the state on periods of a decade or longer. It switches from a cool phase to a warm phase. Winters during a warm phase of PDO are more prone to be warm and dry in Oregon. When both the PDO and ENSO are in a warm phase, the possibility of a warm and dry winter increases in Oregon.
The Climate Impacts Group at University of Washington has done an extensive analysis of ENSO, PDO and their effects on Pacific Northwest Climate.