Chances of El Niño Increase, But it May Be Weak

The chances of an El Niño bringing more precipitation than normal to drought-stricken Southern California this winter have increased since one month ago, but if the weather phenomenon does develop it will likely be weak, a National Weather Service meteorologist said on Thursday.

Eric Boldt, warning coordination meteorologist with the National Weather Service, said the good news is that ocean temperatures in the mid-Pacific have increased in the past month, "reflecting weak El Niño conditions," and the forecaster consensus of an El Niño developing this winter has been raised to 65 percent, from 58 percent in November.

The bad news, Boldt said, is that the atmosphere has yet to connect with the warmer ocean water and rainfall patterns in the equatorial region are not reflecting El Niño conditions.

Further, most forecasting models predict only a weak El Niño this winter, and a late-developing El Niño would not be as beneficial as one that develops earlier in the wet season, he said.

"All El Niño regions are warmer than normal right now," Boldt said, adding that the main area in the mid-Pacific that forecasters track for determining El Niño conditions shows December temperatures are 1 degree Celsius above normal.

Temperatures at least a half-degree Celsius above normal thresholds are generally required to produce a weak El Niño, he said.

"Most models have us in a weak El Niño condition for this winter," Boldt said.

That translates into a forecast of above normal temperatures and chances of precipitation in California for the month of December and beyond, he said.

In the seven days ending Tuesday, most of the state, including southwest California, has seen above-average precipitation, Boldt said.

Above-normal temperatures and precipitation are forecast to continue in southwest California through the main rainy season of January through March, reflecting a "classic El Niño trend of weather storm systems across Southern California compared to the northern part of the state," Boldt said.

"In conclusion, December is starting out wet, but it's still uncertain if the full-fledged El Niño will develop and we're running out of time," he said.

"It's likely that if El Niño occurs it will be weak and historically weak El Niños have resulted in very large precipitation extremes, wet or dry."