From freezing cold to pouring rains, this winter may have a topsy-turvy feel to it, but the people who keep their eyes on conditions in the oceans have no doubt about the pattern of powerful storms now blowing in from the Pacific. It has El Niño
written all over it.
"It's obviously a very strong jetstream howling across the Pacific — what you'd expect with El Niño," said Michael Halpert, deputy director of the National Weather Service's Climate Prediction Center.
El Niño watchers at the CPC have been predicting these wet and windy winter conditions for months now — a circumstance that might have looked a little shaky a few weeks ago when northern cold waves gripped much of the midwest and eastern states.
Atmospheric conditions are flighty and inherently hard to predict, but the set of conditions that go by the name El Niño originate in the ocean, a more stable feature of the system with a long "thermal memory." Detecting the eastward movement of warm tropical ocean temperatures every few years toward the coast of South America allows forecasters — months in advance — to say something about the patterns that can be expected during the next winter. (The unusually warm sea surface temperatures seen in this CPC image along the equator from the International Date Line is a sure sign of El Niño.)
Moving the warm surface water out into the central Pacific changes the trajectory and intensity of the jetstream, pulling farther south a winter storm track that more typically would flow over the Pacific Northwest. So northern states usually experience winters that are drier and warmer than usual, while the US Southwest and Southeast sees wetter and cooler conditions.
"El Niño sets up a background flow, it acts on the jetstream," Halpert said in an interview. "El Niño doesn't make individual storms," although because the jetstream is more invigorated, "the storms are stronger than they might be."
Ocean temperatures have become warmer, and winds have become stronger in recent weeks, reflecting "a strong El Niño," according to the CPC's most recent advisory, and these conditions — and impacts — are expected to persist through Spring.