Weak El Niño Won’t Ease California Drought

The prospects are dwindling for El Niño to help ease California's long-term drought.

Michelle Mead, Warning Coordination Meteorologist with the National Weather Service in Sacramento, said the chance of a strong El Niño is not favored. She said National Oceanic and Atmospheric Administration forecast models show El Niño will peak at weak-to-moderate strength during the late fall and early winter.

Ideally, that could mean rain for California. But Mead said the consensus of forecasters is for El Niño to emerge during August-to-October, peaking only at weak strength.

"If you're planning El Niño to be a very wet winter, the way things are looking right now, if I were a betting person I would not put my money on that scenario," said Mead. "The chances for El Niño development in fall and early winter in the Northern Hemisphere has decreased from 80 percent last month, to about 65 percent this month."

Mead said a strong El Niño event typically brings rain to Southern California. But, with a weak-to-moderate El Niño predicted, she said the possibility for rain in the south is significantly reduced. And, based on historical data, she said a weak El Niño year doesn't bring above-average rain to Northern California.

Mead said the drought in California will not end in 2015, with or without a strong El Niño event, because the water deficit is so extreme.

Drought deficits are so bad it would take near record snow and rain storms to end it.

"The 2015 water year would need 150 percent of average rainfall including 150 percent of snowpack, which means we also need a cooler air mass over California so that we get a thicker and deeper snowpack,” said Mead. “And that would just be to break even, that would not necessarily end the drought but it would definitely help the reservoir situation and get us a little more ahead. But it would not be a drought buster by any means."

The term El Niño refers to the large-scale ocean-atmosphere climate phenomenon linked to a periodic warming in sea-surface temperatures across the central and east-central equatorial Pacific (between approximately the date line and 120^oW), according to NOAA.

El Niño represents the warm phase of the El Niño/Southern Oscillation (ENSO) cycle, and is sometimes referred to as a Pacific warm episode.

NOAA said the term originally referred to an annual warming of sea-surface temperatures along the west coast of tropical South America.