Scientists are increasingly focused on shifting warm Pacific waters as a possible cause for Southern California's lack of predicted winter rain.
The season's El Niño weather phenomenon, characterized by historically warm waters along the equatorial Pacific, was similar to those that triggered record rainfall in Southern California in 1983 and 1998.
Thus, many scientists and weather forecasters reasonably predicted an unusually wet winter for greater Los Angeles. Some even warned that a "Godzilla El Niño" would inundate us with heavy weather.
They were wrong.
Downtown L.A. has seen less than half of normal rainfall this season, and most of the county is still experiencing "exceptional drought" conditions.
Jin-Yi Yu, an earth system science professor at UC Irvine, theorized in a report we published April 7 that warm waters along the equatorial Pacific shifted away from the Americas and toward the Central Pacific, possibly correlating with the jet stream's move north away from Southern California.
In 1983 and 1998, El Niño sent a wet, tropical jet stream into our region. While this year's El Niño was quite similar to that of 1998, it differed when the warmest waters shifted west.
"It behaved like a traditional El Niño from summer to December, but beginning this year it alternated back to a Central Pacific El Niño," Yu said. "The sea surface-temperature warming seemed to shift back to the Central Pacific. This El Niño deviated from the typical El Niño."
Last week a National Weather Service video "recap" of our El Niño winter (embedded below) offered the same theory. Alex Tardy, an NWS warning coordination meteorologist based in San Diego, put the video together.
"We saw less action in the Eastern Pacific which, in turn, can change our jet stream pattern," he says in the video. The shifting warm water "may be one cause to why the jet stream did not respond and pull as far south persistently."
The shifting-water theory, which doesn't yet have a name, is becoming predominant at the weather service, Tardy told us.
"It's actually what our agency is initially hanging our hat on to see if that was the main cause," he said.
Warm waters moved away from the Americas along the equatorial Pacific and, with that shift, moved the jet stream, too, Tardy said. Generally speaking, the warm water and the jet stream seem to go hand-in-hand, he indicated.
"Your jet stream can only cover so many miles before it gets a wiggle in it," Tardy said. "The jet stream was so far west that we were always on the tail end of it. We ended up at 50 percent of a normal rain year.
"It was like a fireman's hose missing the fire," he added.
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Predictions of a stormy "Godzilla El Niño" were, of course, way off. But Tardy said that we had never seen an El Niño behave like this in the 60 or so years scientists have been meticulously tracking Pacific jet streams.
It was supposed to act like 1998, which had plenty of rain and snow well into spring. But it ended up being a one-of-a-kind season.
"Would you be able to predict this?" Tardy said. "Probably not. You could Monday morning quarterback it. But this El Niño was quite rare."