Negative NPM Here to Stay?

Alaska “Blob” Tracker

In my post last month I mentioned that the recent reversal of the North Pacific Mode (NPM) phase was related to this winter’s El Niño event.  In other words, when we saw El Niño developing last year, we might have anticipated that “the Blob” would probably lose some of its surface signature over the course of the winter; it wasn’t a surprise.  The chart below illustrates that this is a typical course of events by showing the evolution of the NPM index in 8 previous winters with the strongest El Niño conditions since 1950 (based on the bivariate ENSO index from November through March).


The thick black line in the chart shows the mean of the 8 similar past years, and we can see that it’s normal for the NPM index to decline quite significantly from the spring prior to an El Niño winter to the summer after an El Niño winter.  This…

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