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I would not consider the positive phase of the PDO to be critical for El Nino's impacts - that's a bit like the tail wagging the dog. If we do see the expected El Nino impacts, particularly in the North Pacific and North America, then I would expect to see a shift toward a more positive PDO. However, if that occurs, it's likely a reflection of El Nino triggering the usual, stronger-than-normal Aleutian low, which then leads to changes of North Pacific sea surface temperatures consistent with the positive PDO. So, I generally would expect a shift of the PDO in the positive direction to accompany El Nino's expected impacts in the winter, but that doesn't mean that the positive PDO is the primary driver of the impacts.

In reply to by Stephen S.