Winter El Nino outlook: Wet S. California, dry Northwest
Forecasters say they are now confident that El Nino’s southern storms will boost rainfall this winter as far north as Sacramento in California, but the Pacific Northwest will likely be drier than normal.
Federal Climate Prediction Center officials said Sept. 10 there’s a 95 percent chance that strong El Nino conditions will persist through the winter before gradually weakening next spring.
During the winter, odds favor increased chances for above-normal precipitation across the southern part of the United States and up the East Coast, officials said.
But the inland Pacific Northwest should anticipate below-normal rainfall, while the Oregon and Washington coasts and much of Northern California have equal chances of above- or below-average precipitation, according to the CPC’s three-month winter outlook.
Temperatures throughout the West are expected to be higher than normal this winter, complicating chances for an abundant snowpack, according to the outlook.
“One thing to caution a little bit is that these are probabilistic forecasts,” Mike Halpert, the center’s deputy director, told reporters in a conference call. “We could be surprised.… There have been a couple of big El Ninos when I don’t think it was really dry anywhere across the country. Everywhere was above normal.
“But the most likely case (in the Northwest) is drier than average conditions,” he said.
El Nino is a warming of the ocean at the equator that interacts with the atmosphere, changing the jet stream that drives the winter storm track. There have been six previous El Nino periods since 1950, and this one has the potential to rate near the top in terms of strength.
Some scientists have characterized this El Nino as a “monster” or “Godzilla” storm track, predicting that it could produce the kind of wet winter that California saw in 1982-83 and 1997-98, when nearly double the state’s average precipitation fell.
However, Halpert said such descriptions are “not helpful” as state and federal officials have worked to tamp down expectations that this winter could end the drought. State Climatologist Michael Anderson reiterated Sept. 10 that past El Nino events have produced mixed results in Northern California, where key reservoirs are situated.
“The fact is that this coming winter could extend our record-dry weather or bring major storms, heavy precipitation and coastal storm surges or a combination of all,” Anderson said in a statement. “We must prepare by conserving water in our daily lives, as well as protecting property against the potential of heavy storms and local flooding.”
Though growers have held out hope that a wet winter will ease drought conditions, it would take as much as three times the average annual precipitation over the next year to make up the cumulative deficit of 71.5 inches of rainfall in the central Sierra Nevada since 2011, officials have said.
Still, a wet winter would be a big reprieve in the San Joaquin Valley, where growers denied their normal surface-water allocations have depleted aquifers to the point that the ground is sinking in many areas.
“As we enter a new water year on Oct. 1, there’s a lot of uncertainty about what that water year will bring,” said Kevin Werner, the National Oceanic and Atmospheric Administration’s director of western regional climate services. “It’s entirely possible we could see continued drought across many areas of the West.”