Weather Window | Where last winter stands water-wise
October 9, 2013
TAHOE/TRUCKEE, Calif. — Sept. 30 marked the end of the 2013 water year, making it an appropriate time to look back to see where last winter stands water-wise.
Officially, the 2013 WY ended on June 30 for California's coastal regions and interior valleys. The lowlands calculate annual precipitation based on a July 1 to June 30 calendar cycle. In the Sierra, however, the water year runs from Oct. 1 to Sept. 30. Early October is traditionally the time of year when reservoir storage and stream flow are at their lowest levels. It's also the time of year when winter sports enthusiasts start getting itchy for snow.
It may seem counter intuitive to those who remember how last winter suffered from an extraordinarily long period with little snowfall, but the 2013 water year came in at an impressive 92 percent of average for the Northern Sierra Precipitation Index. This 8-Station Index includes precipitation gages from Mount Shasta City south through Blue Canyon (Interstate 80) and Pacific House (Highway 50). Considering the erratic nature and annual variability of Sierra winters, precipitation values within 10 percent of average should be considered within the "normal" range.
It's easy to forget that the 2013 winter season started off with drenching rainstorms that initially put the region on pace to exceed the Northern Sierra's wettest winter of record (1983). At the Central Sierra Snow Laboratory near Donner Pass, hydrologist Randall Osterhuber measured a total of 45.7 inches of precipitation in 2013, a respectable 89 percent of normal. (Precipitation is rain and snowmelt combined.) On the other hand, only 215 inches of snow fell there, a measly 53 percent of average.
At the Snow Lab, the winter of 2013 is the fifth least snowiest since 1878. Squaw Valley tallied a season total of 326 inches of snow at its upper mountain stake located at 8,200 feet, which is more than 1,000 feet higher in elevation than the Snow Lab.
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This is how crazy the 2013 winter turned out. In the Northern Sierra, November and December was the ninth wettest of record for the two months combined. Higher snow levels limited substantial accumulations to the upper elevations that laid down a healthy base for the upcoming ski season.
During the Christmas-New Year holiday vacation, a series of cold, powerful storms delivered more "pow" for skiers and boarders. By New Year's Day, Squaw Valley's upper slopes had picked up nearly 21 feet of snow. And even the lower mountain, which had lost much of its base during an earlier rain event, had received another 12 feet of snow.
It was the best start to a winter since the epic 2011 season, which ranks as the ninth snowiest of record at the Snow Laboratory.
But then, in a stunning weather pattern reversal, the next three months — January, February, and March — were the driest on record for the region. With the storm door slammed shut Pacific weather systems detoured around the Tahoe Sierra. It was an unprecedented dry spell for the Tahoe-Truckee region.
GONE, GONE, GONE
Tahoe City received only 2.68 inches of water during the period — statistically the wettest time of year, that averages more than 16 inches of precipitation — which set a new record as the driest three-month stretch since measurements began in 1910. According to Bay Area meteorologist Jan Null, San Francisco's January through April rainfall total of 3.32 inches was the least amount since measurements began in the 1849 gold rush.
Statewide, the Jan. 1 snowpack stood at a robust 140 percent of average for the date. By April 1, however, the time of year when the snowpack statistically reaches its greatest water content, surveys indicated a snowpack at only 42 percent of average. The winter had turned into a bust.
Kelly Redmond of the Western Regional Climate Center said the extreme flip-flop was like Dr. Jekyll and Mr. Hyde, an allusion to a man with polar personality disorder depicted in Robert Louis Stevenson's classic 1886 novella, "The Strange Case of Dr. Jekyll and Mr. Hyde."
Long-range forecasts for winter 2014 are all over the map, and with no strong ENSO signals in the Pacific Ocean. the Climate Prediction Center has broad-brushed California with an outlook for a normal range of temperatures and precipitation.
A wet winter would help alleviate the persistent drought conditions of the Far West, especially in Nevada. The CPC admits that its forecast confidence is low due to the ENSO-neutral conditions, but since Tahoe resorts normally pick up between 30 to 40 feet of snow in an average winter, normal would be good enough in 2014.
Weather historian Mark McLaughlin is a nationally published author and professional speaker. His award-winning books are available at local stores or at http://www.thestormking.com. You can reach him at email@example.com. Check out Mark's blog at http://www.tahoenuggets.com.