Drought-busting El Niño looking less likely Phenomenon looking unlikely to ease drought

Average sea surface temperature (SST) anomalies (°C) for the week centered on 30 July 2014. Anomalies are computed with respect to the 1981 - 2010 base period weekly means. Average sea surface temperature (SST) anomalies (°C) for the week centered on 30 July 2014. Anomalies are computed with respect to the 1981 - 2010 base period weekly means. Photo: NOAA Photo: NOAA Image 1 of / 74 Caption Close Drought-busting El Niño looking less likely 1 / 74 Back to Gallery

Hope of an El Niño rescuing California from its devastating drought this year appears to be just about gone.

Not only have climate scientists downgraded the strength of a potential El Niño, but a report released Thursday by the U.S. Climate Prediction Center indicates that the odds of an El Niño happening at all have decreased.

El Niño is a warming of the Pacific Ocean that tends to influence worldwide weather. Strong El Niños have often been associated with wet winters in Northern California, something the state could use after three straight years of below-average rainfall.

Although Thursday's climate report suggests that an El Niño is still likely this fall or winter, scientists said the chances had dropped from 80 percent in earlier assessments to 65 percent.

The reason for the more pessimistic outlook, said climate scientist Michelle L'Heureux, is that warmer-than-usual surface temperatures in the equatorial Pacific measured this spring have since cooled.

The same underwater swell that pushed heat to the surface, known as a Kelvin Wave, is having its normal counter-effect, but that effect has been much stronger than usual and has moved more cold water up farther than expected, L'Heureux said.

"We're still banking on seeing a reinvigoration of El Niño," she said. "But with that said, we wanted to lower our projections because there are structural weaknesses that have made this El Niño less likely."

The federal forecast calls for the El Niño to be weak or moderate. The consensus earlier this year was that the event would be at least of moderate strength.

San Francisco's wettest rainy season in the last century came during the strong El Niño of 1997-98. Weak and moderate El Niños, however, have sometimes been associated with abnormally dry years in Northern California, even while bringing more rain to Southern California.

The absence of a strong El Niño doesn't sentence Northern California to a dry winter. Warm equatorial surface waters are just one harbinger of wet weather, and any number of factors could trigger rain in the months ahead.