• Michael O'Keeffe

The Pineapple Express and the Wild Winter of 2017


Heavy snow falls near Mammoth Lakes, California in January of 2017.

Winter is coming which means it's time for the stormy season on the West Coast. For much of the year, the North Pacific High, a semi permanent high pressure center (clear weather) that sits off the coast of California, keeps the Golden State's climate dry and sunny. The high essentially acts as a barrier forcing low pressure systems (stormy weather) to go up and around. In winter however, the North Pacific High weakens and follows the sun south towards the equator. This opens the door for powerful low pressure systems to drop down from the frigid north and bring stormy weather to the West Coast between October and April.

One of the most interesting phenomenon that occurs during the winter season on the West Coast is the Pineapple Express. Yes, it's the name of a movie (a pretty funny movie at that), but it is also important in understanding the mechanics of winter weather on the West Coast. High in the atmosphere you have what is called the jet stream, a narrow current of air that flows from west to east around the Earth typically in the middle latitudes (the US and Europe in the northern hemisphere). As the jet stream streaks across the Earth it is manipulated by the high and low pressure systems that it passes by. These pressure systems can bend the jet stream into what are known as troughs and ridges (similar to ocean waves). Troughs tend to be associated with low pressure systems (stormy weather) and ridges tend to be associated with high pressure systems (clear weather).

When the jet stream interacts with low pressure systems over a water source (typically the ocean), it draws moisture into the atmosphere. The low pressure system then can carry that moisture long distances picking up additional moisture along the way where it will then hit land, cooling quickly, and fall in the form of rain or snow. In the North Pacific, particularly powerful low pressure systems can draw deep tropical moisture from Hawaii and carry that moisture northeast eventually slamming into the West Coast, thus the nickname Pineapple Express. This intense narrow band of moisture is what is known as an atmospheric river. These rivers of water vapor can last for days or even weeks pumping huge amounts of moisture through the atmosphere resulting in heavy rain and mountain snow on the West Coast.

Water vapor image of the Pineapple Express. Image courtesy: NOAA NESDIS

7-Day Precipitation Forecast (January 3-10, 2017) courtesy: NWS

The Winter of 2017: A Pineapple Express for the Ages

The winter of 2017 was a particularly memorable storm season for the West Coast, especially for California. A series of powerful, long lasting atmospheric rivers in January and February rode the Pineapple Express straight into the Golden State setting many records for both rain and snow. I happened to be living and working as a liftie at the small ski resort June Mountain in June Lake, California at the time. June Lake is a short 15 minute drive north of the popular ski resort town of Mammoth Lakes on the eastern edge of the Sierra Nevada. June Mountain Resort is owned and operated by the much larger Mammoth Mountain Resort.

The winter of 2016-2017 started off quite slow when I arrived at the end of November. Snow was scarce everywhere in the Sierra, even the high country. In fact, June Mountain had to push their opening day back two weeks due to the lack of snow. Luckily a small storm came through putting down enough snow to get us going. After a busy holiday with little snow to speak of, the great Pineapple Express was on the move, ready to pull into the station.

The first event occurred between January 3 and January 13 in the form of two major long duration systems. What transpired over these 10 days in the state of California and especially in Mammoth and the eastern Sierra was something I'll never forget. The first major system arrived in Northern California on January 2 bringing the usual bout of heavy rain to the soggy Redwood forests of Humboldt and Del Norte counties. Things began to get dicey on January 3 as the system dove southward into the rest of northern California. Over the next 72 hours, the Sierra would experience heavy snow with the Lake Tahoe area taking the brunt of the storm. Squaw Valley Resort on the west side of Tahoe would up with a whopping 83" between January 2 and January 5. Further south, Mammoth Mountain received a more modest 40" between January 4 and January 5. On the coast, heavy rain fell across much of northern and central California with the mountains above Santa Cruz and Big Sur recording the highest amounts between 4-6+ inches in just 24 hours.

Blizzard conditions occur in June Lake, California during the record breaking storms of January 2017.

The first system was just a warm up of what was to come however. After a brief reprieve on January 6, rain and snow began to fall again on January 7 across northern California. In Mammoth, snowfall amounts were moderate picking up about 8 inches during the day. Later that night, the Pineapple Express was about to ramp up in a big way. An unusually strong surge of warm subtropical moisture pushed into the Sierra warming the air quickly. This sent the rain/snow line up to nearly 10,000 feet above sea level in just a few hours. June Lake and Mammoth Lakes sit at roughly 7,700 feet and Lake Tahoe sits at about 6,200 feet. This meant the heavy snow was about to transition to heavy rain. For this reason the National Weather Service issued a Flood Watch which stated the following:


AN ATMOSPHERIC RIVER WILL LIKELY PRODUCE A PERIOD OF INTENSE RAINFALL WITH SNOW LEVELS RISING AS HIGH AS 9000 TO 10000 FEET EARLY SUNDAY MORNING TO MONDAY MORNING. RAINFALL TOTALS OF 6 TO 12 INCHES WEST OF HIGHWAY 395 WITH 2 TO 5 INCHES OF RAIN FOR COMMUNITIES ALONG HIGHWAY 395. THIS INCLUDES BRIDGEPORT, LEE VINING, WALKER AND MAMMOTH LAKES.


6-12 inches of rain! Rain! There are parts of California that don't see that much rain in a year let alone in 24 hours, following a major snowstorm, at 7,700 feet above sea level in mid January. But rain it did, sometime in the overnight the snow finally transitioned to rain. When we woke up on January 8 it was dumping rain about as hard as I had ever seen it fall. This is coming from someone who grew up in Kansas in the middle of Tornado Alley! Understandably, both June Mountain and Mammoth Mountain had to shut down due to the rain. Thunder and lightning accompanied the rain which was flooding the streets around town since storm drains were blocked by mountains of snow from the previous storm. Later that night the cold front finally arrived in the Sierra so the National Weather Service issued a new Winter Storm Warning for Mono County and Lake Tahoe stating the following:


TIMING: HEAVY RAIN WILL TRANSITION TO SNOW MONDAY MORNING WITH PERIODS OF HEAVY SNOW CONTINUING THROUGH WEDNESDAY NIGHT. * SNOW ACCUMULATIONS: 4 TO 8 FEET ABOVE 7000 FEET WITH 1 TO 3 FEET AT LAKE TAHOE LEVEL. 1 TO 2 FEET FOR COMMUNITIES ALONG HIGHWAY 395 IN MONO COUNTY. * WINDS: SOUTHWEST 15 TO 25 MPH WITH GUSTS TO 45 MPH. SIERRA RIDGE GUSTS OVER 100 MPH.


4-8 FEET of snow! FEET! Given June Lake and Mammoth Lakes elevation at 7,700 feet we were in for a long couple days. When the sun rose on Monday, January 9 the heavy rain had transitioned back to heavy snow. Another 1-2 feet would fall during the day as the Pineapple Express was getting ready to pack one last final hurrah. The next day the wind picked up dramatically and the snow intensified, so much so the National Weather Service issued a Blizzard warning for Mono County. The wind and snow ended up shutting down US395, the main highway that connects June Lake and Mammoth Lakes to basically the outside world. The resorts continued to be shut down for the third day in a row. And to make matters worse the combo of snow, rain, and snow made for unstable snow conditions causing avalanches that blocked the main road into June Lake meaning the only way out of town was the back way which took you to US 395, which, like I mentioned earlier, was closed in either direction. We were trapped.

The blizzard conditions continued into Wednesday, the snow piled up, and the roads continued to be shut down as were the resorts. On Thursday, January 12 the winds finally subsided but the snow did not, Mammoth Mountain would receive the largest 24 hour dump of the entire storm with 28 inches falling. All told by the morning of January 13, the Sierra had been walloped. Record breaking storm total snowfalls were being reported from Tahoe to Mammoth. At Mammoth Mountain, 103 inches were observed between January 7-13. Further north at Lake Tahoe, Squaw Valley recorded 102 inches between January 8-13. Tacked on to the totals from the first storm, Mammoth received 143 inches of snow or 12 FEET in just 10 days! Squaw Valley received 185 inches or 15 FEET! The coast of California also observed record breaking amounts of rainfall. In the mountains above Big Sur and in the coastal hills of Sonoma County north of San Francisco reports of over 25 inches of rain fell between January 3 and January 13. Landslides from the heavy rain had destroyed a section of Highway 1 in Big Sur shutting down the highway in either direction. Repairs would end up taking almost a year to complete making Big Sur nearly inaccessible.

A stormy day at Morro Bay on the Central Coast of California in February of 2017.

Following the first storm series things didn't settle down for long. A second Pineapple Express was barreling towards California yet again. The storm fortunately was a bit weaker, but that wasn't saying much. Regardless, snow and rain began to fall over most of California on January 18 and continued until January 24. Mammoth again experienced very heavy snow and strong winds effectively shutting down US395 yet again. Storm total snowfall in Mammoth topped out at 101 inches in just 7 days! January of 2017 ended with 244 inches of snow for the resort making it the snowiest month on record for Mammoth Mountain. It was getting to a point when there was no where left to put the snow that was being plowed. Trucks were literally hauling snow from parking lots and roads in town to dump it in the sagebrush outside of town. The days following would end up being the best powder days I've ever experienced skiing once the lifts got turning again.

February also proved to be quite stormy with two more prolonged atmospheric river events. Heavy rain and snow continued to plague the state. By the end of February an additional 163 inches of snow had fallen in Mammoth and 201 inches fell at Squaw Valley in Lake Tahoe. Fortunately, March and April while still active were much quieter than the first two months of 2017. Amazingly, the endless train of storms aboard the Pineapple Express were able to dump so much precipitation on California that it effectively ended the 10 year drought the state had been enduring. Tens years of relentless drought ended in just two months. The once severely depleted reservoirs were full again, even a little overfull in some spots (Oroville Dam for example). The typically dry dusty coastal hills of central and southern California sprang alive turning a verdant green. The Pineapple Express had brought life back to California. It was a wild ride, but the end result was quite beneficial. An extraordinary weather phenomenon I was lucky to witness first hand.


Following a record wet winter, the coastal hills of California's Central Coast turn verdant green in February of 2017.

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