Craig Miller

Sunset on San Pablo Bay. Coastal areas saw a balmy end to September, accompanied by air quality alerts.

The Great American Heat Wave of 2012 arrived later in California than in many parts of the country — and it’s in no hurry to leave.

Having nudged the upper 90s on Sunday, Sacramento closed out the month of September with a record 26 days of 90-plus highs, surpassing the 1974 record of 24 days. The trend is forecast to continue into the first several days of October, with a chance of hitting 100 for the first time since mid-August. Farther north, Sacramento Valley towns like Redding and Red Bluff are suffering similar bake-offs.

Dry heat persisted up and down California, accompanied by red-flag warnings for fire danger along the South Coast. Of course, it’s that time of year, when the sea breeze backs around and “offshore flows” become the dreaded Santa Anas (in the south) and Diablos (in the north), notorious for fanning catastrophic wildfires. Air quality suffers during these periods, even without fires. Air quality regulators placed a Spare-the-Air Alert in effect for Monday in the San Francisco Bay Area.

For a vivid visual review of the world’s extreme weather in 2012, the World Resources Institute constructed a timeline of major events, which currently runs through August and WRI says it plans  to continue updating.

By Andrew Freedman

Photo by Sandy Huffaker/Getty Images

In 2010, a series of strong storms linked to El Niño caused major flooding in Southern California.

If you thought the first six months of the year were chock full of weird weather events, just wait — according to climate scientists there is an increasing likelihood that El Niño conditions will soon develop in the tropical Pacific Ocean. El Niño events, which are characterized by an area of unusually warm sea surface temperatures in the tropical Pacific Ocean, can have a huge influence on global weather patterns. Its effects on the U.S. tend to peak during the winter.

The U.S. has already had a record warm January-to-June period, and has already had two extremely rare heat waves this year, one in March and the other in mid-June to early July. Entering mid-summer, drought conditions are covering 56 percent of the lower 48 states, a record drought extent in the 21st century.

Depending where you’re located, the prospect of a new El Niño event may be good news. The drought-parched Texas Panhandle, for example, tends to be wetter during El Niño years. It could also be decidedly unwelcome news — just ask residents of California who dealt with El Niño-related flooding in 2010.

El Niño is a natural source of climate variability, and typically occurs every three to seven years. The question of whether manmade global warming will influence El Niño cycles is an area of active research. One recent study does suggest, though, that global warming could intensify the effects of an El Niño episode, even if it doesn’t influence its occurrence.

NOAA

During El Niño, the sea surface temperature in the Pacific Ocean is warmer than normal.

Citing factors such as warming ocean temperatures in the tropical Pacific, the Climate Prediction Center, which is part of the U.S. National Oceanic and Atmospheric Administration (NOAA), said on July 5 that there is a better than 50 percent chance that El Niño conditions will develop sometime between July and September.

Because of El Niño’s effects on seasonal climate conditions, farmers and ranchers, ski area operators, water planners, hurricane forecasters, and many more closely monitor such El Niño forecasts.

Tony Barnston, chief forecaster for the International Research Institute for Climate and Society, which works with the Climate Prediction Center, said an El Niño event could help relieve the ongoing drought conditions in some areas, but potentially worsen the drought for others.

“The southern tier of U.S. states tends to have above-normal precipitation during winter when there is an El Niño. So this would be helpful for the droughts currently lingering in Texas/New Mexico, and Georgia/Alabama,” he said in an email conversation. “It would not help the ones in Kentucky/Indiana though, and could cause a new one in the northern Rockies.”

El Niño events can also help boost global average surface temperatures. A strong El Niño event led to the record warm year of 1998, and some climate scientists, including NASA’s James Hansen, have pointed out that a new El Niño event would likely lead to another record warm year given the combination of El Niño and manmade global warming.

NOAA

Sea surface temperature index in the tropical Pacific Ocean, showing the cycle of El Niño events (warmer than average) and La Niña events (cooler than average).

A strong, two-year La Niña event, which was characterized by cooler-than-average sea surface temperatures in the tropical Pacific, dissipated in April of this year, and it held down global average temperatures somewhat.

This El Niño event, if it does occur, is more likely to be on the weak-to-moderate end of the spectrum, according to Barnston.

One of the key indicators that El Niño conditions are developing is a growing area of warmer-than-average equatorial Pacific sea surface temperatures, and an increase in the oceanic heat content as well. “The observations . . . reflect a likely progression towards El Niño,” the Climate Prediction Center said.

Forecasters use computer models to help anticipate El Niño and La Niña events. Right now, most of the simulations of air and sea conditions show a developing El Niño.

According to Barnston, who is a veteran researcher and forecaster of El Niño events, there are many unknowns that forecasters are currently facing. “We don’t know, first, whether there will be an El Niño or not. Currently we think there is about a 60-70 percent chance for one, and a 30-40 percent [chance] of not having one,” he said. “If we do get one, we don’t know how strong it would be. We doubt it will be a giant one like 1997-98 because those usually develop by May or even earlier. But it could be moderate or weak. Most of us think it is likely to be in either of those two categories, and think that it would last from about August through January.”

The development of an El Niño or La Niña event depends on feedbacks between the ocean and atmosphere, and Barnston said that currently the prevailing weather pattern in the tropical Pacific is not particularly conducive to El Niño formation, despite the warming sea surface temperatures, but this could change. “We’re in a transition stage,” he said.

“The development of El Niño depends greatly on what happens in the coming two months. If we do not get at least some development by the end of August, then the chances of getting development later become much lower.”

A version of this post also appears at Climate Central, Climate Watch’s content partner.

Craig Miller/KQED

California has not experienced the extreme heat much of the rest of the country has this summer.

For more than a week, record-breaking temperatures have been baking the Midwest and East Coast. But while cities in other parts of the country broke and tied records for the hottest Fourth of July, in San Francisco I bundled-up in a couple sweaters and watched the fireworks through the fog. Which is typical. Overall, it’s been an average summer here in California, at least temperature-wise.

“At June around the state, most places were fairly close to normal, or a degree and a half below normal, so not any real extremes,” Jan Null, a meterologist with Golden Gate Weather Services, told me. “We’ve stayed in the mild, in-between area. It was not a particularly cold winter, and not a particularly hot summer.”

Western Regional Climate Center

While the rest of the country suffers from record-breaking heat, the West Coast has had average and below-average temperatures this summer.

The jet stream moves high- and low-pressure systems around the world, like huge waves. In the summer, the pattern slows down. This summer, it’s stalled out completely, locking a high-pressure system over the eastern part of the U.S.

“Any time you have extremes, whether it be flooding or any other pattern, the atmosphere gets locked into a state of equilibrium,” Null said.

As long as that high pressure is parked in the East, a low-pressure system, with its lower temperatures, will stay locked in place on the West Coast.

“This isn’t unheard of or necessarily that unusual,” Kelly Redmond, a climatologist at the Western Regional Climate Center, said. “It’s not necessarily the case that the West Coast is obliged to go along with the rest of the country, just the way California is different in almost all of its features.”

The extreme heat in the rest of the country gives us clues into what scientists say climate change could bring. So what does that mean for California, and this — so far — mild summer?

“That has been an ongoing discussion in the state of California,” Redmond said. “The way it’s looking now, if the state were to warm up, the interior, let’s say I-5, would warm faster than Highway 101 or Highway 1.”

So for the coast, at least for the next few decades, this summer could be what climate change looks like, too.

“We’re going to end up some degrees warmer a few decades in the future, but how we get there, it may not be a straight line,” Redmond added. “Think of it like a play, like you’re watching a play in so many acts. Eventually you get to some kind of conclusion, but what makes it interesting is how you got there, the way it unwound. That’s what I find so interesting.”

Read the full text version of this story at KQED’s QUEST site.

Craig Miller

East Brother Island, with the 19th-century lighthouse on the left and fog signal building on the right.

On foggy mornings, I wake up to a faint symphony of foghorns. From my condo on a windy bluff above the Mare Island Strait, the horn on the Carquinez Bridge is the bassoon in the back row, accompanied by the assorted boops and beeps of all the other fog signals within earshot of where the Sacramento River empties into San Pablo Bay.

But the orchestra plays a different tune than it did in decades past. Technology and politics are changing the navigational soundscape of coastal America. Complaints from coastal residents about the repetitive blasts of sound and modern electronic navigation aids have relegated the foghorn to a lesser role in the maritime chorus.

In fact, the iconic “BEEE-ohhh” of the old-fashioned air-powered “diaphone” has virtually disappeared from the score. To my delight, one of the last few diaphones still in working order turns out to be a short drive and five-minute boat ride from my house.

The old diaphone on East Brother Island (officially the Walter Fanning Fog Signal) has been silenced for the purpose of navigation. But Peter Berkhout, who, with his wife Dina, maintains the bed & breakfast in the old lighthouse, has kept the diaphone in superb shape and will crank it up for occasional demonstrations.

Driven by a diesel-power air compressor installed in the 1920s, the horn was originally steam-operated.

“There used to be a big brick hearth with a coal pit and a water tank,” Berkhout explained, “and it would take about 45 minutes to go from cold to having enough steam pressure to blow the horn.”

When the pressure comes up and Berkhout flips the switch, no matter how well you prepare yourself, it’s impossible not to jump just about out of your shoes when the diaphone goes off (you can hear a couple of blasts in my radio story). The sound bounces off the nearby Richmond bluffs and echoes back to the island, washing over you a second time. “I guess you can learn to sleep through anything but I’m glad I haven’t had to learn to sleep through this.”

Craig Miller

The current foghorn at East Brother Island, near Richmond, CA, is electronic and solar-powered.

East Brother Island still has a foghorn, but let’s face it: technology has drained most of the romance out of it. The modern descendent of the Fanning diaphone is a pillar barely bigger than a fire plug, and compared to its predecessor, practically whispers its warning. It’s powered by a solar panel attached to a 12-volt battery. The guys on the Aids to Navigation team at the Coast Guard station on Yerba Buena Island in San Francisco Bay tell me the biggest maintenance challenge is people stealing the batteries.

What sets off a foghorn?

In the old days, fog signals were manned 24-7. When the visibility dropped to a certain point, they’d start up the horns, each of which still has a particular timing signature. Harbor pilot Greg Waugh can still recite them, even though he retired in 2007.

“Center span of the Golden Gate Bridge is two blasts every 40 seconds,” he recalls. “South tower is one blast every 20 seconds. Lime Point on the north tower is one blast every 30 seconds.” He can go on. These signatures allow any sailor with a stopwatch to figure out where he or she is.

Today some horns, such as East Brother’s operate continuously during certain seasons. Others are activated by electric eyes that measure the density of the water vapor in the air. And Waugh says a new system under development will allow ship masters & pilots to activate local signals with their radios.

Waugh says a few years ago, he and his fellow pilots estimated that each year brings about 1,500 hours of fog to the Gate. If you’re doing the math, that means the fog is in almost 20% of the time. Waugh says that while modern aids like GPS and the AIS network for commercial shipping are great, fog-enshrouded mariners can use all the help they can get. “Navigating the fog is like driving down the highway with your hood up,” he says.

John Huseby

Heavy rain flooded the parking lot at San Francisco's Ocean Beach over the weekend.

California’s water supply is in better shape after this weekend’s storms and the wet weather earlier in the month (though the parking lot at San Francisco’s Ocean Beach is in worse shape). The water content of California’s snowpack is hovering around fifty percent of what’s considered “normal” for this time of year — not quite cause for celebration but much better than it had been; on February 28, the date of the most recent manual snow survey, water content was only 30% of normal.

So this winter isn’t going to be the driest on record, or even the second-driest, but it’s bound to be on the dry side, regardless of what happens now. It’s just too late in the year to catch up, even with more storms heading our way this week.

Department of Water Resources

In Northern California, this year, shown in pink, was dragging along near the driest years on record, but precipitation has been better in the last month.

So far, Northern California’s had more precipitation than the Southland but the National Weather Service is forecasting more widespread rain and snow beginning tonight.

California Department of Water Resources

In Southern California, precipitation is at 55% of normal for this time of year.

Most of the state’s reservoirs are near normal levels for this time of year — some are even above normal — thanks to the very wet winter last year.

The upcoming “April 1st” snow survey (actually scheduled for next Monday, the 2nd), is closely watched, as this is the time when the Sierra snowpack generally reaches its peak.

Craig Miller

Rain comes late to Northern California: A March storm front hovers over San Pablo Bay, north of San Francisco.

Last week’s State of the Climate report issued by the National Oceanic and Atmospheric Administration found that this winter is stacking up as the warmest since 2000 and the fourth warmest on record in the contiguous United States.

According to NOAA, 47 of 48 states experienced above-average temperatures in the period between December and February, with the greatest increases seen in the Northeast and Midwest.

Only New Mexico saw below-average temperatures.

In spite of the Bay Area’s balmy winter, California’s average temperatures during the three-month span were only slightly above average — and .2 degrees Fahrenheit cooler than last year during the same period.

NOAA

Deke Arndt, chief of NOAA’s Climate Monitoring Branch, said the nation’s warmer weather is partly attributable to a phenomenon known as the Arctic Oscillation, or AO, which is a determinant in how far north or south the jet stream will be situated. “This year’s index was ‘positive’ for most of the winter,” Arndt told me. “This is an indicator that the jet stream will stay further north.”

Arndt compared the influence of the Arctic Oscillation to playing with a jump rope. The more positive the index, he said, the more the rope is pulled taut. “There is a stronger pressure gradient between the mid and upper latitudes, which means that the jet stream tends to get ‘locked’ further north and cold air from the arctic does not penetrate as far into the interior of North America.” Conversely, Arndt said, last year’s wild winter can be partly attributed to a “negative phase” of the oscillation, he said, which contributes to greater variability in the latitude of the jet stream and increased likelihood of arctic air being drawn over the continental U.S.

Arndt noted, however, that there is a complex set of factors at play in determining temperature including this winter’s ocean conditions in the Pacific — known as La Niña — and feedbacks from long-term warming. “Rarely does a single factor dominate all results in all places,” he said.

NOAA

Kelly Redmond, a climatologist with the Western Regional Climate Center, cautioned against extrapolating too much from the data. “From winter to winter, the warm areas tend to move around a bit,” Redmond wrote.  “With La Niña we tend to see cool and wet/snowy conditions along the northern tier states and warmer, drier conditions along the southern tier.”

The last three months have not merely been warm but dry, particularly in the Pacific Northwest and California, which, according the report, is in the grip of its second driest recorded winter. “Storms coming onto the West Coast have either been shunted north, or torn apart before reaching California,” wrote Redmond. “We look to be in a respectable wet pattern later this week. Maybe the wettest episode of the winter for the northern half of the state and mountains.”

One study cited in the NOAA report, published by the Rutgers Global Snow Lab, pointed out that the area of snow cover across the U.S. was the third smallest it’s been in 46 years of satellite data.

According to the report, a full 39% of the country was in the midst of a drought. However, the percentage classified as D4 or “exceptional” drought shrunk, from 3.2 to 2.5%, largely the result of a spate of recent wet weather in Texas and the Southern Plains.

Overall, 2011 was the 11^th warmest year globally since record-keeping began in 1880.

Some atmospheric scientists think that could change soon.

By Andrew Freedman

While some may be cheering the lack of snow as welcome relief, the widespread lack of it spells trouble for the ski industry, which pumps billions into the wintertime economy in states from California to Maine, and requires cooperation from Mother Nature to stay in business.

Craig Miller/KQED

Snow from last year's big winter storms could still be seen on the mountains near Lake Tahoe on August 30th. This winter has been one of the driest on record.

Ski area operators across the country are already reporting drops in lift ticket sales, and are hoping for a major change in the weather pattern to bring colder, snowier weather. So far, die-hard skiers have been forced to either ski on man-made snow or travel to one of the few far-flung areas that have benefited from the unusual weather, such as the mountains of New Mexico or Alaska (where one town has had 18 feet of snow).

Compared to last winter, this wimpy winter weather is coming as quite a shock.

Snow was so widespread last winter that at one point in January, every state except Florida had some snow on the ground. But this year, the U.S. had the 11th least extensive December snow cover in the 46-year satellite record, said David Robinson, the director of the Global Snow Lab at Rutgers University.

“Is it fair to call it a snow drought? We’re getting there,” Robinson said. “It’s certainly an early season snow drought.”

Michael Berry, president of the National Ski Areas Association, said this winter is noteworthy for how many ski areas are seeing below average snowfall. “Typically, we have one region or another in the country that might be off to a slow start. But the thing about this year that’s somewhat unique is that it’s kind of an across-the-country problem, at least to date.”

Nowhere is the contrast from last winter so evident as in California’s Sierra Nevada Mountains, home to Lake Tahoe’s ski resorts.

National Oceanic and Atmospheric Administration (NOAA)

Observed snow depth on December 29, 2010 (top) and December 29, 2011 (bottom).

Last year, skiers hit the slopes all the way through July 4th, and several mountains set all-time seasonal snowfall records, with totals surpassing 65 feet. Squaw Valley, for example, received a staggering 810 inches of snow.

This December, at nearby Alpine Meadows, just 1.5 inches of snow fell, well below the average of 72.3 inches, and far below last year’s 134-inch December total.

The lack of snow has allowed Yosemite’s Tioga Pass, a road that would normally be buried in snow by now, to remain open later than at any time since record-keeping began in 1933.

In the Northeast, an October blizzard and other early season snows were followed by warm temperatures that melted the natural snow cover, and prevented ski areas from making snow. With a recent shot of cold air, New England’s ski resorts have finally cranked up their snow making operations, but attendance is down from last year, in part due to the bare ground in major media markets, such as New York and Boston. With just a trace of snow in December, Boston had its second-least snowiest December on record, for example.

“Psychologically, we do better when people see snowfall in their backyards,” said Bonnie MacPherson of Okemo Mountain in Vermont, where skier visits were down about 30 percent compared to last year over the same Christmas holiday week. “We’re fortunate in that we’ve invested pretty heavily in the snow-making system that we have,” she said.

With each passing day of below average snowfall, it becomes more difficult to make up for lost time, especially when spring is arriving earlier on average due in part to global warming. This forces ski area operators to squeeze the same amount of earnings into a shorter time period.

Rutgers’ Robinson said ski areas would have to rely more on the President’s Day school vacation week in February to compensate for lost revenue during the Christmas holiday period. “Many of the ski resorts are going to have to really count on it this year because they were hurt by the holiday week between Christmas and New Year’s,“ he said. A poor turnout during that week could mean ski areas are “going to be running in the red.”

Forecasters are quick to caution, though, that the rest of the winter may not play out the same way that the season has started. Much depends on two key factors that affect winter weather in North America: La Niña and the Arctic Oscillation.

Two Very Different La Niña Winters

La Niña, which is a natural climate cycle characterized by cooler than average water temperatures in the tropical Pacific Ocean, tends to nudge the wintertime storm track to favor heavier snows in the Pacific Northwest, northern Rockies, Ohio Valley, and northern New England.

But this winter has not been behaving like a typical La Niña winter. Instead, storms have moved across southern California, into New Mexico and Colorado, and then on up into the Midwest.

Klaus Wolter, a researcher at NOAA’s Earth System Research Lab in Boulder, CO, said there are indications this will change later this month. “I’m pretty confident that it will probably revert back to more typical La Niña winter weather,” he said.

Part of the reason why this winter has departed so dramatically from La Niña’s script has to do with the Arctic Oscillation, which is a pattern of atmospheric pressure that helps steer the jet stream in the Northern Hemisphere. When it’s in a “positive phase” as it has been so far this winter, cold air tends to remain bottled up in the Arctic. So far in 2012, 130 daily high-temperature records have been broken in California alone.

Wolter and many other forecasters think the Arctic Oscillation may shift during the next few weeks, making it easier for a more typical La Niña weather pattern to emerge. This would begin to favor ski areas in the Pacific Northwest and northern Rockies, such as Jackson Hole, Wyoming and Big Sky, Montana.

A version of this post also appears at Climate Central, a content partner of Climate Watch.

Ken Murphy / Murphlab

Detail from Ken Murphy's video sky mosaic

About two years ago, Ken Murphy set up a tripod on the roof of San Francisco’s Exploratorium science museum and aimed his video camera at a particular patch of sky. He’s spent the two years since shooting time-lapse sequences from his makeshift observatory and has stitched them together into this wonderful visual tableau.

Murphy, who is a web developer at KQED and a former artist-in-residence at the Exploratorium, says the project grew out of — well — boredom. He became restless with his experimentation with art works using LED lights. He says he was looking for more natural movement. So Murphy went dumpster-diving for parts and cobbled together a computer-controlled camera that would record the same sky segment every ten seconds, around the clock. He says it took two years of shooting to stitch together one full year of images. Eventually he found himself sorting through three million video frames for the mosaic.

But Murphy didn’t want his frames to be too predictable, so he settled on a sky patch about 45 degrees above the northern horizon, where neither the sun nor moon would enter the picture.

Given his location on the tip of the San Francisco peninsula, what you do see is plenty of fog and rain. Murphy says viewers are often surprised at “how much blue” is in the finished piece.

Alexander Tarrant

Murphy with his rooftop camera rig

Murphy says “Patterns that occur in nature sort of resonate with people,” though he wanted to capture something “outside our immediate scope of perception.” He thought some kind of time-lapse imagery would provide that. “I wanted to have a certain fluidity to it,” he told me.

On Murphy’s site are several earlier stages of the work, which are also interesting to watch. He says he’s now working with a team from the Exploratorium on a time-lapse study of tides. We’ll be watching that one, too.

Precipitation outlook for winter 2011-12, showing the likelihood of below average precipitation in Texas and other drought-stricken states.

Does this mean Texas is toast?

By Michael D. Lemonick

As most Californians know, El Niño is a periodic unusual warming of the surface water in the eastern and central tropical Pacific Ocean. Actually, that’s pretty much a lie. Most people don’t know the definition of El Niño or its mirror image, La Niña, and truthfully, most people don’t much care.

What you do care about if you’re a Texan suffering through the worst one-year drought on record, or a New Yorker who had to dig out from massive snowstorms last winter (tied in part to La Niña), or a Californian who has ever had to deal with the torrential rains that trigger catastrophic mudslides (linked to El Niño), is that these natural climate cycles can elevate the odds of natural disasters where you live.

At the moment, we’re now entering the second year of the La Niña part of the cycle. La Niña is one key reason why the Southwest was so dry last winter and through the spring and summer, and since La Niña is projected to continue through the coming winter, Texas and nearby states aren’t likely to get much relief.

But Niñas and Niños (the broader cycle, for you weather/climate geeks, is known as the “El Niño-Southern Oscillation,” or “ENSO”) don’t just operate in isolation. They’re part of the broader climate system, which means that climate change could theoretically change how they operate — make them develop more frequently, for example, or less frequently, or be more or less pronounced. Climate change could also intensify the effects of El Niño and La Niña events.

Climate scientists have been wrestling with the first question for a while now, and they still don’t really have a definitive answer. Some climate models have suggested that global warming has already begun to cause subtle changes in ENSO cycles, and that the changes will become more pronounced later this century. But a new study, published in the Journal of Climate, doesn’t find much evidence for that.

But on the second question, the new study is a lot more definitive. “Due to a warmer and moister atmosphere,” said co-author Baylor Fox-Kemper, of the University of Colorado in a press release, “the impacts of El Niño are changing even though El Niño itself doesn’t change.”

That’s because global warming has begun to change the playing field on which El Niño and La Niña operate, just as it’s changing the background conditions that give rise to our everyday weather. The Texas drought is a prime example. It’s most likely cause is reduced rainfall from La Niña-related weather patterns. But however dry Texas and Oklahoma might have been otherwise, the killer heat wave that plagued the region this past summer — the sort of heat wave global warming is already making more commonplace — baked much of the remaining moisture out of both the soil and vegetation. No wonder large parts of the Lone Star State have gone up in smoke.

A map of sea surface temperature anomalies, showing a swath of cooler than average waters in the central and eastern tropical Pacific Ocean - a telltale sign La Niña conditions.

When the next El Niño occurs in a year or two, it will probably bring heavy rains to places like Southern California, whose unstable hillsides tend to slide when soggy. Except now, thanks to global warming, the typical El Niño-related storms that roll in off the Pacific may well be turbocharged, since a warmer atmosphere can hold more water. This is the reason, say many climate scientists, that downpours have become heavier in recent decades across broad geographical areas.

La Niña, plus the added moisture in the air from global warming, have also been partially implicated in the massive snowstorms that struck the Northeast and Mid-Atlantic states during the last two winters. Those could get worse as well, suggests the new analysis. “What we see,” says Fox-Kemper, “is that certain atmospheric patterns, such as the blocking high pressure south of Alaska typical of La Niña winters, strengthen…so, the cooling of North America expected in a La Niña winter would be stronger in future climates.” So to pre-answer the question that will inevitably be asked next winter: no, more snow does NOT contradict the idea that the planet is warming. Quite the contrary.

Finally, for those who really do want to know what El Niño and La Niña actually are, as opposed to what they do, you can go to NOAA’s El Niño page. But be warned: there will be a quiz, and the word “thermocline” will appear.

A version of this post also appears at Climate Central, a content partner of Climate Watch.

Matthew Green

An early snow in the Grouse Lakes area of the Sierra Nevada

By Matthew Green

For months now, I had reserved the second weekend in October for my annual grand finale “summertime” backpacking trip. Culminating an unusually short warm season, this was to be the ceremonial final alpine lake swim, the last mosquito bloodletting until well after next year’s thaw. Which is why, as my partner and I proceeded to pitch our tent in about 10 inches of snow last Friday evening, I couldn’t help but feel I’d been had.

Last week’s storm, which swept across the northern half of California early Wednesday, dumped up to a foot of snow in the Sierra’s high peaks, with accumulation as low as 5,000 feet. According to the Central Sierra Snow Lab, this is the first snowstorm in 96 days – since July 1 – marking the shortest duration between storms in the Sierra since 1969.

Green surrounded by white in the Sierra

Don’t get me wrong. It was absolutely gorgeous. We hiked – or more accurately, trudged – a few miles into the Grouse Lakes Area, a basin in Tahoe National Forest at just over 6,000 feet, where ridges of polished granite cascade into a necklace of shimmering lakes. Add a blanket of white covering the forest duff, dotted with  majestic cedars and pines,  and the scene was downright breathtaking. Not one mosquito, either. And even though the conditions for us over the weekend were gorgeous, with cloudless blue skies and daytime highs reaching into the low seventies, there was still plenty of snow on our way out Sunday afternoon.

Despite the earlier forecasts of blustery conditions in the area, we assumed (with little rationale aside from denial), any frigid weather this time of year would steer clear of anything below, say 7,000 feet. Evidently, not so.

“October is like a half-and-half month; there are dry Octobers and wet Octobers,” said Johnnie Powell, a weather forecaster at the National Weather Service’s Sacramento office. “This was a December-like storm. It’s not rare but it isn’t normal, either.” And by next weekend, he added, after a warm rain system followed by several days of dry weather reaching into the 70’s, most of the wintry evidence will be gone.

And oh, just for the record: as promised, I did take that final swim, a straight dive into a beautiful snow-encrusted lake, and a very swift exit out. I don’t regret it, but I might not recommend it.

Matthew Green is the education outreach specialist for KQED News.