Whither the weather?

Vane (named appropriately enough) asks the experts 

What a difference a year makes. Last December, according to Mammoth Mountain Ski Patrol Data, Mammoth was buried in 197.5 inches of snow. This year: Locals and visitors alike are wondering not only when Mammoth will see its next snowfall, but whether this pronounced change is a result of seasonal luck-of-the-draw, or something more sinister: climate change.

As Jet Propulsion Laboratory (JPL) Climatologist Dr. Bill Patzert put it, “The question is, how did we get from snowmageddon to where’s the snow?” The answer is La Niña.

La Niña, the flip side of the more commonly known El Niño, is a quasi-periodic climate pattern that affects the tropical Pacific Ocean, and from there, weather all around the globe.

When prevailing winds along the equator push the warm water of the Pacific Ocean to the west, they leave colder water in the east along the coast of California. This leads to a dry winter in California and wet weather in the western Pacific and Australia. This weather pattern is known as La Niña.

When the winds slacken, warm waters slosh back again from west to east, warming the ocean along the coast of California. Where water goes, rain goes, and this usually leads to a wet winter in California, while the western Pacific and Australia see drier weather. This pattern is known as El Niño.

“So this is a sloshing type of cycle we experience,” said Dr. Graeme Stephens, Director of the Climate Sciences Center of JPL. “Sometimes the cycle is quite weak, other times it’s quite strong, as in this case.”

In a La Niña year, storms tend to be diverted to the northwest (to Washington State, British Columbia, and Alaska), leaving central California and the southwest, including Arizona and New Mexico, with below-average precipitation. This year has followed that typical La Niña pattern, and “storms from off the Pacific that would usually bring Mammoth snowpack have been too far north,” Dr. Patzert explained.

But here’s where things get confusing: last year was a La Niña winter as well, yet Mammoth experienced a record breaking 661.5 inches of snowfall. “Last winter, La Niña was tempered by a series of storms out of the north because the jet stream was wild and wooly and unconstrained,” said Patzert.

In fact, as Professor Richard Seager, at the Lamont-Doherty Earth Observatory of Columbia University, explained, the epic storms that brought so much snow to Mammoth last December were the result of a “Pineapple Express,” a meteorological phenomenon that carries extreme damp air from Hawaii to California. This precipitation fell as snow in Mammoth in several severe storms. “That can just happen,” said Dr. Seager. “That’s why we issue these [seasonal] forecasts in terms of probabilities, not certainties.”

Dr. Patzert noted that this about-face from an extremely wet winter last year to an extremely dry winter this year is not unusual for a grouping of years defined as El Niño or La Niña, nor is it unusual for seasons in the state of California. “The variability from year to year definitely gives you whiplash,” he said.

Forest Service data confirms this fluctuation with evidence of a drought winter of only 94 inches in 1976-77 (an El Niño year), to a wet winter of 487.5 inches in 1977-78 (also El Niño). The data, found at http://patrol.mammothmountain.com/MMSA-SnowSummary70-Current.htm, offers several other examples of these seasonal and El Niño/La Niña reversals.

But does climate change come into this equation at all? Dr. Stephens, Dr. Patzert, and Seager agreed that while this winter may not be the direct result of climate change, it might be a sign of things to come. “No one cycle like this can be attributed to climate change, but the expectation is that the cycles will intensify as our planet’s climate warms, bringing more extreme wet and dry periods,” said Dr. Stephens. “So what we are experiencing is perhaps the harbinger of what we might expect in the future.”

This doesn’t mean that all winters will be dry, but that dry and wet periods will be exaggerated. Wet periods in the Sierras may also be more rainy than snowy due to global warming, Dr. Seager said. “Expect less snow and more rain.”

But Dr. Seager added that these changes would happen “over decades. If you’re planning on going skiing sometime soon, I wouldn’t worry about it. If you’re planning on going skiing in 2030, you might want to think about it.”

What does all of this mean for Mammoth in the winter of 2011-12? For now, local business owners, employees, and MMSA are keeping their hopes up. “We’re doing everything we can to keep as much terrain open as possible,” said MMSA Communications Director Joani Lynch. “We know it’s going to snow, and we’ll be ready when it does.” Lynch noted that the number of skier visits is down from this time last year by 20%, but she added that this number is still impressively small, “considering what the conditions are like around the country.”

“Here’s the good news,” said Dr. Patzert: “usually the snowiest, wettest months [in the Sierra Nevadas] are January, February, and March.” Although only 2 years on record have been drier than the current year (86-87 and 96-97, according to data collected from the snow pillow at Mammoth Pass, a look at the Running Total Precip Ski Patrol graph from 1983-current (http://patrol.mammothmountain.com/SWEChart.png) shows that many years experienced a leap in snowfall in January onward.

Also good news, according to the National Weather Service Climate Prediction center, “A majority of the [La Niña] models predict a weak or moderate strength La Niña to continue through the Northern Hemisphere winter and then gradually weaken after peaking during the December – January period.”

The bad news: “the forecast for the next 10 days is definitely dry,” said Dr. Patzert. “Either we’re going to get a wipeout, or potentially we’ll get lucky and see a late snow season. But at this point, smart money, which is me, is betting drier than usual.”