[californiadisasters] La Niña 2010-11 Wettest in History

La Niña 2010-11 Wettest in History

By Alex Tardy and Miguel Miller
Coast To Cactus Weather Examiner ~ April 2011

In the last issue of Coast to Cactus we discussed the record month of December 2010 and specifically the period December 16-22 which brought heavy rain, flooding and landslides to Southwest California and a Federal Disaster Area designation. January through March brought mostly drier than normal conditions (for details see the Quarterly Summary). The combination of a wet October (10 days of measurable precipitation at San Diego), the record month of December, and a cold and occasionally wet February and March led to the wettest La Niña on record dating back to the winter of 1931-32. Overall, December 2010 was the wettest of any year for the coastal climate zone of Southwest California which includes Los Angeles, Orange and San Diego Counties. The state of California overall was very wet, and snow-pack in the Sierra Nevada reached 175 percent of normal on April 1. Several ski resorts that keep records in the Sierra Nevada broke all-time seasonal snowfall exceeding 600 inches. No one is more surprised that a wet winter has just ended in California than one of the world's leading experts on oceans. "I guess we were wrong," laughed Dr. William Patzert during a presentation to Southern California water managers. Dr. Patzert, who is an oceanographer with NASA's Jet Propulsion Laboratory in Pasadena, reminded his audience that the anticipated drought in parts of Arizona, New Mexico and Texas, still exists as we enter the normally dry summer months.

The La Niña conditions are still very notable in the equatorial Pacific Ocean where cooler water temperatures exist. They had most forecasters predicting a dry winter in California, where a drought declaration had existed since 2008. In fact, since records were first kept, there was an 82% probability that the La Niña would mean a dry winter. "While the La Niña condition certainly existed, it isn't always the primary indicator of the type of weather we are going to experience. What we call a very active negative arctic oscillation in the Northern Hemisphere drove unexpected cold and wet weather into the Golden State," said Dr. Patzert. December 2010 was the wettest December in the city of Los Angeles since 1889. The rainfall amount in Los Angeles in December alone was over 10 inches, over 60% of the total annual rainfall.

"In reality, we had a dry winter except for two weeks in December," said Dr. Patzert who noted that January, February and March were relatively dry. Across Southwest California, precipitation was 4 to 8 inches above normal during the 2010-11 winter across most areas except the de-serts. The south facing mountain slopes of the San Bernardino Mountains ended up 15 to 20 inches above normal with the wettest of those locations receiving 50 to 60 inches of precipitation! The period October to December 2010 was nearly the wettest on record for Southwest California since 1931 (99.3 percent) considering all years, not just La Niña. The beneficial precipitation brought an official end to the drought, declared by California's Governor with support from the US Drought Monitor. Reservoirs filled significantly or even exceeded capacity in Southwest California (e.g., Lake Hodges). The moist ground and vegetation will bring a delay to the fire season but we all know too well that drier or warmer than normal conditions could return as early as our normal dry summer season. The Climate Prediction Center outlook calls for the best chance of warmer than normal conditions for Southern California inland areas and the Desert Southwest through September. The ENSO conditions in the equatorial central Pacific are expected to become neutral, or little signal for our weather pattern.

Source: http://www.wrh.noaa.gov/sgx/newsletter/current-newsletter.pdf

--
Check out http://groups.yahoo.com/group/californiadisasters/
Read our blog at http://eclecticarcania.blogspot.com/
Visit me on Facebook at http://www.facebook.com/derkimster

__._,_.___

Be sure to check out our Links Section at http://groups.yahoo.com/group/californiadisasters/links
Please join our Discussion Group at http://groups.yahoo.com/group/californiadisasters_discussion/ for topical but extended discussions started here or for less topical but nonetheless relevant messages.

Your email settings: Individual Email|Traditional
Change settings via the Web (Yahoo! ID required)
Change settings via email: Switch delivery to Daily Digest | Switch to Fully Featured
Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe

__,_._,___