El Nino's Nemesis, The PDO, Helps Protect the Northwest Coast This Year

We are now at the height of a very warm El Nino and some folks are worried.

Some worry about lack of precipitation and snowpack.

But as I have noted in a previous blog, the very strongest El Niños generally bring near-normal precipitation and mountain snows to our region.

Others worry about Northwest coastal flooding due to Kelvin waves moving up the coast from Southern California (see sample below).

The truth is that El Nino and accompanying coastal Kelvin waves shouldn't pose a serious flooding threat to our coast.

In an earlier blog, I described Kelvin waves and how they weaken when they move north up the West Coast.  Stronger over southern CA, but greatly weakened up our way.

But there is another reason you should not lose sleep about coastal flooding:  

Another mode of natural ocean variability, the Pacific Decadal Oscillation (PDO), will be fighting it. 

Let me explain.

El Nino produces a certain warm-water pattern as shown below (from yesterday), with warmer than normal water over the tropical Pacific and along the southwest US and Mexican coasts.  Our sea surface temperatures (SST) are far closer to normal in such years.

El Nino strengthens and weakens (into La Niña) over a period of roughly 5-7 years.

The Pacific Decadal Oscillation produces a similar temperature pattern to El Nino during its warm phase (see below).

But here is the key point.  

The PDO varies on a time scale of many decades and is currently in its COLD phase, and thus is OPPOSING the warm El Niño.   It is also relatively strong on our coast.

As shown below, we have mainly been in a cold phase during the past several years.

The PDO cold phase tends to bring below-normal water levels to our coast.  Since the PDO is generally weaker than El Nino, that means it tends to reduce the El Nino signal in temperature and sea level rather than eliminate it.  

Sea surface temperatures are not quite as warm.  Sea level is not as high.

You can see this by looking at sea level at La Push on the Washington Coast from October 1 to today. (below). Normal conditions are shown by the light blue; red is this year.

During the past month, sea level has been slightly higher than normal. A modest addition, but nothing serious.  

Minor flooding is shown by the brown band.  We never reach it.   No worries.  

Want more proof that PDO is our friend?  

Here is the long-term trend of sea level at Toke Point on the Washington Coast (below).  

You will note that there is essentially no long-term trend.

The highest sea level years were during two strong El Niño years (1983, 1998), indicated by the red arrows. But the latest strong El Nino year (2024-25) was not exceptional because the PDO was quite negative.

We will enjoy PDO  "protection" this year as well, so predictions of El Nino flooding on the WA coast by certain local media outlets and some social media channels are exaggerated. 

Colder and Snowier than Normal in the Northwest: This is NOT the Classic El Nino Pattern

The Northwest atmosphere did not get the message about El Nino this week, with colder-than-normal temperatures and substantial snowfall in the mountains.

For example, a veritable army of snowplows moved through Snoqualmie Pass this morning

See the video here.

Stevens Pass was quite snowy this afternoon

The visible satellite image this morning was a classic, showing instability showers offshore, the result of cold Arctic air passing over much warmer water.

The radiosonde sounding (balloon-launched weather instruments) at Forks indicated a freezing level of around 1300 meters above sea level (around 4200 ft).   The snow level can be as much as 1000 ft below that.  

No wonder the passes got snow.

With the cold/snow conditions over the region, several mountain locations have had above-normal snow amounts the last few days (see below). The blue dots indicate stations with over 150% of normal snow!.  That does say much this early in the season.

The colder-than-normal conditions, with more mountain snow, are not over!

The forecast of the temperature anomaly from normal shows for the next day indicates that the whole Northwest will be colder than normal (blue and green colors).

And colder-than-normal conditions will continue over the region for the next week!

The result will be additional early-season mountain snow, as shown by the predicted accumulation through Sunday afternoon (below).

There has been a lot of loose talk about coastal Kelvin waves and warm ocean conditions off our coast, but our water temperatures are actually quite close to normal (see below).

The warmer-than-normal coastal waters are mainly to our south over central and southern California and offshore far to our southwest.

Finally, the models are emphatic that there will be a major weather regime change in a week, when a series of potent atmospheric rivers will aim directly at our region (see below). Should really help to fill reservoirs.

Quite a contrast to classic El Niños that take the moisture plumes into California.

All in all, good news for water resources in the Northwest.