Weather Window: El Nino is back and Tahoe area snow lovers are starting to salivate | SierraSun.com
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Weather Window: El Nino is back and Tahoe area snow lovers are starting to salivate

Photo couresty NOAA
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It’s back. The National Weather Service Climate Prediction Center (CPC) has posted an ENSO alert, predicting that El Nino conditions will continue to develop and are expected to last through next winter. Although no one can say with certainty how the developing El Nino will effect Lake Tahoe’s weather, skiers and snow boarders are already salivating at the prospect of a heavy winter.

But it’s too early to predict how strong the ENSO (El Nino Southern Oscillation) event will be. At this time the computer models are in disagreement over the eventual strength of this El Nino, but according to the CPC and#8220;current conditions and recent trends favor the development of a weak-to-moderate strength event into the Northern Hemisphere Fall 2009, with further strengthening possible thereafter.and#8221;

The term El Nino translates from Spanish as and#8220;the boy-child.and#8221; Peruvian fishermen originally used the term and#8212; a reference to the and#8220;Christ childand#8221; and#8212; to describe the appearance, around Christmas, of a warm ocean current off the South American coast. Normally the trade winds along the equator push the warmest waters into the western portions of the Pacific toward Asia, but on an irregular cycle of two to seven years El Nino conditions alter this scenario. Lasting from as little as six months to as long as four years, ENSO events cause the trade winds to weaken, or sometimes even reverse direction, allowing warmer-than-normal water to accumulate along the equator in the central and eastern Pacific Ocean. This change in ocean movement often caps the upwelling cold current, which disrupts fishing along the South American coast around Christmas, with its greatest effects during the winter months.



The warming of equatorial sea surface temperatures not only affects fisheries and marine life, but also global precipitation patterns. Strong El Ninos generally cause cold, wet winters over the southeastern United States and drought in the north-central states. In the Pacific Northwest, ENSO conditions bring drier than average winters 75 percent of the time. Generally speaking, the greatest chance for above normal precipitation is focused on Southern California, with decreasing likelihood for locations further north.

Historically, ENSO events have caused both dry and wet winters in the Sierra, with the influence on precipitation related to the strength of the event. Data on El Nino go back more than 140 years, but sea surface temperature readings are more reliable after World War II. Using data recorded since 1945, meteorologist Jan Null, a former lead forecaster for the National Weather Service in San Francisco, has made an analysis of eight strong (Type 1) El Ninos. The results suggest that California has a 70 percent chance of above normal precipitation in a Type 1 event, with the best chances for wetter than normal weather from December to February.



Out of the eight strong El Nino events studied, San Francisco enjoyed five wet winters and Sacramento six. Los Angeles was wetter than normal all eight seasons. Considering that the Central Sierra storm track often follows the Interstate 80 corridor, if the sea surface temperatures get warm enough over the next five months, the odds are good that abundant snow and rain will fall on your favorite ski resort. Keep your fingers crossed.

and#8212; Weather historian Mark McLaughlin is a nationally published author and photographer. His award-winning books are available at local bookstores or at http://www.thestormking.com


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