Wintertime climate here on the North Coast swings between wet and slightly less wet. Temperatures are relatively mild, with freezing weather less common than for our neighbors east of the Coast Range. If the oracles at the National Oceanic and Atmospheric Administration’s (NOAA) Climate Prediction Center are accurate, this winter could be considerably cooler and wetter than normal because of a climate phenomenon called La Niña.
By now most of folks have heard the terms El Niño and La Niña. These Spanish terms classify two ranges of climate conditions that relate to sea surface temperatures (SSTs) and the movement of winds (and therefore storms) across the Pacific Ocean. You can see an example of what NOAA experts look at in the SSTs in the graphic below. The colors in this graphic (courtesy of the NOAA Climate Prediction Center) represent differences between water temperature, not actual temperatures, and reflect the period from September 30-October 7, when compared with an average of temperatures taken from 1971-2000. Blue is cooler than normal while yellow, orange and red represent warmer temperatures. Notice that the cooler water extends far across the equatorial Pacific. If this strengthens throughout the fall, then the impact of La Niña on our weather will likely be stronger, as I will explain below.
While the planet is a seemingly big place, two great energy transferring mechanisms—water and air—bring distant portions of our world closer together through climate teleconnections—or connections that act over considerable distances. As temperatures in waters of the equatorial Pacific warm, the trade winds which blow storms across the ocean from western to eastern ends (where the coasts of Asia and North America sit respectively), tend to drive storms to the southeastern direction–and into Southern California and Mexico. This is a product of El Niño climate status. Locally, a persistent low pressure system called the Aleutian Low migrates to the south and west, driving storms away from our coast. We will thus tend to be warmer and drier during El Niño winters. That means stream flow will tend to be lower. This not a hard and fast rule, however! Some El Niño periods have produced record flooding (for example the winter of 1982-83). Most, however, tend to be drier than normal.
It’s opposite, or La Niña is caused when those same equatorial waters cool from normal (usually one to two degrees, which for the area involved is considerable). The result is that trade winds are driven in a north eastern direction. At the same time, the Aleutian Low tends to weaken and move farther to the north. The result–again a trend only–tends to be wetter and cooler than normal winters.
These two periods swing back and forth during a 2-5 year cycle in which one follows the other. Like a pendulum swinging, the energy of the Pacific Ocean and the atmosphere must balance out in the end. We can usually expect El Niño-driven conditions first followed by La Niña-produced conditions in our neck of the planet. To make matters more complicated, this see-saw is influenced by conditions in the overall Pacific and Atlantic oceans with regular climate shifts that may take decades to become apparent.
Back to the North Coast, besides a wetter than normal winter, what does this mean for you? If you are concerned with floods and storm surge, then be prepared for the La Niña years. If you are interested in fishing our streams and estuaries, higher than normal flows can be good for migrating salmon and steelhead–or at least better than years of low flow. Historically, however, salmon harvest off the Oregon coast declined dramatically during the El Niño events of 1958 and 1983. We do not fully understand how changes associated with the climate affect salmon. It is likely that changes in ocean conditions associated with El Niño and other events interact, and, in effect, serve to decrease a young salmon’s chance of survival.
So, while we might not be stormier than normal, it would be a good idea to keep your hats on and your hatches battened down this winter!
