El Nino, under some conditions, also creates Pineapple Express storm conditions in the American River Watershed, which creates more rain and run-off for us: as noted in our upcoming water report (9/24/06):
“In this decision- making process, the ongoing threat of pineapple-express storms, fueling the recent flooding in 1986 and 1997, are a crucial factor, as Dettinger (2005) concludes:
"The long-term perspective taken here reveals that, historically, El Nino conditions have favored having more low-altitude precipitation (relative to the usual high altitude orographic [influence of mountains on precipitation, airflow etc.] enhancement) that, falling most often as rain rather than snow, may tend to increase flood risks. Pineapple express patterns and the flood risks that they entail, on the contrary, appear to have been favored by near-neutral (non-El Nino) tropical conditions during El Nino-rich decades (warm phases of the Pacific Decadal Oscillation).
"Furthermore, this long-term perspective confirms our suspicion that the risks for flood generation in the American River basin are special in several ways. With its broad expanses of moderate-altitude terrain and its near equal mix of rainfed and snowmelt runoff, the basin is particularly sensitive to storm-by-storm variations in the amounts and distributions of rainfall. The orientation of the western slopes of the Sierra Nevada in the modulated year-to-year increases in orgraphic precipitation enhancement during La Nina winters, rivaled in the Sierra Nevada only by the southern ramparts of the range where topography may favor El Nino orographic enhancements. Pineapple express storms bring particularly warm and wet storms to the area and thus pose important flood risks. On long-term average, the American River has the dubious distinction of being situated beneath the margins of most intense precipitation associated with pineapple-express circulations and of being situated at the point in the Sierra Nevada and Cascades where pineapple-express circulations (on average) bring the warmest temperatures. (p. 72, highlighting added) "
(p. 33)
An excerpt from the article.
El Niño Returns
By Richard A. Kerr ScienceNOW Daily News13 September 2006
The National Oceanic and Atmospheric Administration (NOAA) announced today that the ocean warming that is El Niño has returned to the tropical Pacific Ocean. A month ago, both human forecasters and computer models had some inkling of the worldwide weathermaker's return, but a sudden warming ushering in El Niño caught them by surprise. Experts predict that the warming could bring some good news: a reduction in hurricane activity in the Atlantic Ocean.
El Niños occur every 3 to 7 years, bringing patches of unusual warmth, dryness, coolness, wetness, and combinations thereof to various parts of the world. The last such event happened in 2003. In its monthly "discussion" issued 10 August, NOAA's Climate Prediction Center (CPC) in Camp Springs, Maryland, had noted that winds and ocean warming had in recent months begun to favor a weak El Niño by the end of the year and that the forecast models were leaning that way too. Within just a week or two, however, the surface waters of the tropical Pacific Ocean began warming faster, a hefty 1°C by early September. That was enough to convince forecasters as well as their models that "we have got the beginnings of an El Niño, and it's going to continue," says CPC's Vernon Kousky. Some of the models are calling for the weak beginnings to strengthen into a moderate El Niño.
Even the beginnings of an El Niño are reworking the weather, CPC forecasters are saying. Today's discussion reports that all of Indonesia, Malaysia, and most of the Philippines have been drier than normal. That dryness is likely to continue for the rest of the year, it says, as typical wintertime El Niño effects develop around the world.
An El Niño effect of particular interest to Americans is the way a tropical Pacific warming tends to suppress Atlantic hurricane activity. The Atlantic hurricane season is just picking up after a slow start, Kousky notes, and this El Niño is still weak at midseason. But NOAA hurricane forecasters are figuring that, if anything, the ongoing Pacific warming will dampen late-season hurricane activity. That would be good news for U.S. coastal residents and anyone looking to consume oil and gas from the Gulf of Mexico.
