Weather Window: Winter’s opening punch in Tahoe/Truckee
November 24, 2010
TAHOE/TRUCKEE, Calif. and#8212; No doubt about it, the recent winter storms hit with a powerful punch and launched Tahoe’s nascent ski season into the national spotlight. Some regional resorts were buried under more than 8 feet of powder, treating early winter sport enthusiasts to top to bottom coverage. The wet storms in October and these early snowstorms are good news for both the local economy and depleted water levels in Lake Tahoe.
Last year’s above average winter season was impacted by warmer than normal sea surface temperatures in the Pacific Ocean. During this past summer however, ocean temperatures cooled. The Climate Prediction Center has issued a La Nina advisory for 2011 meaning this winter’s weather pattern will be influenced by La Nina conditions in the Pacific. La Nina is the term used when equatorial sea surface temperatures are cooler than normal. In stark contrast to El Nino conditions, the La Nina-influenced jet stream pattern often leads to cooler and wetter conditions in the Pacific Northwest and a drier than normal winter in California, especially southern regions of the state. Northern California is on the border between the two regions and can swing either way, with Interstate 80 about the pivot point.
For the Truckee-Tahoe region, La Nina-influenced winters are often a toss-up when it comes to precipitation. In 1924, cooler than normal surface temperatures cut off Pacific storms and produced the Sierra’s driest winter on record. But similar conditions during the winter of 1907 altered the storm track and blasted the Sierra with snow, setting California’s all-time seasonal snowfall record of 884 inches (more than 73 feet) at Tamarack south of Lake Tahoe. And La Nina winters sometimes unleash torrential rain in the mountains and spawn lowland flooding. Western Nevada’s worst flood in history happened during a weak La Nina episode in early January 1997 and caused damage exceeding $500 million to the Reno-Sparks area.
The Dr. Jekyll and Mr. Hyde characteristics of La Nina will keep forecasters guessing as we move into the winter months. Dr. Kelly Redmond, deputy director and regional climatologist of the Western Regional Climate Center in Reno says La Nina conditions, and#8220;Seem to raise the odds in the Sierra Nevada of wintertime floods.and#8221; Redmond studied the La Nina connection on the American River between 1933 and 2000 and found it caused water flows on the American River to average 60 percent greater than in El Nino-influenced winters, indicating a substantial likelihood of flood.
The reasoning behind the flood possibility is La Nina episodes appear more likely to tap the so-called Pineapple Express, a train-like series of tropical storms that can funnel warm and heavy rain into the Sierra. Nine out of 10 floods in the Sierra are these wet mantle events when high elevation rain melts the existing snowpack. Some of the most notable flood events on the Truckee River have occurred during La Nina-influenced winters, including the washouts of November 1950 and December 1955 and 1964. California’s top 10 floods all came during La Nina years.
The official long -range forecast for this December, January and February, based on the La Nina episode, is calling for above normal precipitation in the Pacific Northwest and below average for Southern California. According to Elissa Lynn, a senior meteorologist with the California Department of Water Resources, is that statistically, La Nina years that start out dry generally stay dry, running about 50 to 90 percent of normal precipitation for the year. Since significant storm activity is already underway this year, it could be a harbinger of better things to come.
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and#8212; Tahoe 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 firstname.lastname@example.org