Strengthening El Niño impacts on Lake Tahoe region: too fickle to predict

TRUCKEE, Calif. — As the Pacific Ocean continues its warming trend amid shifting trade winds, scientists agree that future El Niño-spurred weather in California could provide a variety of effects for the Lake Tahoe region.

However, while some news outlets can get away with publishing headlines describing El Niño’s potentially miraculous impacts on the drought-riddled state, Jan Null, a meteorologist with Golden Gate Weather Services in Saratoga, said there is more to it than that.

“It’s complicated,” Null said.

A July report released by the National Oceanic and Atmospheric Administration’s National Weather Service indicates a significant increase in Pacific surface water temperatures and strengthening equatorial westerly winds reflect an ongoing and strengthening El Niño.

There is now a “greater than 90 percent” chance that El Niño conditions that began in March will contribute to a wet winter, according to the report, and it represents a 5 percent increase from June and a 40 percent increase from March.

Null described a strong El Niño as a disruption in weather patterns over the Pacific Ocean — when its surface warms, it releases heat, which in turn causes wind directions and jet streams to change. Those anomalies, he said, are historically linked to wetter weather in California.

When it comes to predicting El Niño anomalies, Null said scientists love running models — lots and lots of models. Accordingly, of all models run coinciding with the report’s findings, nearly all predict El Niño to continue into the Northern Hemisphere’s 2015-16 winter, “with many multi-model averages predicting a strong event at its peak strength.”

“Forecasters like any time you have consistency in the computer models,” Null said. “You want the same story from one model run to the next.”

How those models apply to specific regional weather — especially when talking about the snowy, more-typical winter weather one associates with the Tahoe region — things get less consistent.

Stuck in the middle

Brian Brong, a meteorologist with the National Weather Service who focuses on the Tahoe region, said that while it may be true models suggest increased precipitation is on the horizon, it doesn’t necessarily mean that precipitation will guarantee an increased snowpack this winter, he said.

“We’re kind of in the middle in terms of certainty,” Brong said in literal and figurative terms.

Geographically speaking, Tahoe resides in a region where it could just as easily be impacted by the warmer, wetter storms not typically associated with strong snowfall (generally known as “pineapple express” storms), as it could by colder, arctic weather patterns, which, while less wet, can produce more snow accumulation, Brong said.

Null looks at the last Tahoe winter and believes it got a bad rep, due in large part to people’s expectations.

“If we had had the same storms be cold, producing snow, the amount of water that would have melted and gone into the reservoirs would have been less,” Null said, because a warmer atmosphere can retain more water than a colder one.

What Brong said he could predict with near certainty is that whatever precipitation this El Niño anomaly does bring, it is almost certain to be followed by another drought, whether it’s next year or 10 years from now.

“There have been pretty big El Niño winters,” Brong said, noting the winter of 1997, an especially popular and fortuitous one in terms of precipitation and snowfall that scientists have been pointing to when comparing what could be this year and what once was.

Still, while both Brong and Null agree all evidence suggests the latest El Niño will bring a wet winter, neither can predict whether or not that will directly translate into a large snowpack for the Tahoe region.

“I am cautiously optimistic that we are going to have a strong El Niño,” Null said. “What that means, however, is what we don’t know.”