- Pineapple Express
Pineapple Express (also known as Pineapple Connection) is a non-technical, shorthand term popular in the news media for a meteorological phenomenon which is characterized by a strong and persistent flow of atmospheric moisture and associated heavy rainfall from the waters adjacent to the
Hawaiian Islands and extending to any location along the Pacific coast of North America. The Pineapple Express is driven by a strong, southern branch of the Polarjetstream and is usually marked by the presence of a surface frontal boundary which is typically either slow or stationary, with waves of low pressure traveling along its axis. Each of these low pressure systems brings enhanced rainfall.The conditions are often created by the
Madden-Julian oscillation , an equatorial rainfall pattern which feeds its moisture into this pattern. They are also present during anEl Niño episode.The combination of moisture-laden air, atmospheric dynamics, and
orographic enhancement resulting from the passage of this air over the mountain ranges of the West Coast causes some of the most torrentialrain s to occur in the region. Many Pineapple Express events follow or occur simultaneously with major arctic troughs in the Northwestern United States, often leading to major snowmelt flooding with warm, tropical rains falling on frozen, snow laden ground. Examples of this are the December 1964 Pacific Northwest flood and theWillamette Valley Flood of 1996 .A Pineapple Express battered
Southern California fromJanuary 7 throughJanuary 11 ,2005 . This storm was the biggest to hit Southern California since theEl Niño of 1998. [ [http://www.ocregister.com/ocr/sections/news/focus/article_416548.php News: Jet stream unleashed the rains - OCRegister.com ] ] The storm caused mud slides andflooding , with one desert location just north ofMorongo Valley receiving about 9 inches of rain, and some locations on south and southwest-facing mountain slopes receiving spectacular totals:San Marcos Pass , inSanta Barbara County , received 24.57 inches (624 mm), andOpid's Camp in theSan Gabriel Mountains ofLos Angeles County was deluged with 31.61 inches (803 mm) of rain in the five day period.The unusually intense rain storms that hit south-central Alaska in August 2006 were termed "Pineapple Express" rains locally.
The
Puget Sound region fromOlympia, Washington toVancouver, BC received several inches of rain per day in November 2006 from a series of successive Pineapple Express storms that caused massive flooding in all major regional rivers and mudslides which closed the mountain passes. These storms included heavy winds which are not usually associated with the phenomenon. Regional dams opened their spillways to 100% as they had reached full capacity due to rain and snowmelt. Officials referred to the storm system as "the worst in a decade" onNovember 8 2006 . Portions of Oregon were also affected, including over 14 inches (350 mm) in one day at Lee's Camp in the Coast Range, while the normally arid and sheltered Interior of British Columbia received heavy coastal-style rains. In British Columbia especially, Pineapple Express systems typically generate heavy snowfall in the mountains and Interior Plateau, which often melts rapidly because of the warming effect of the system. After being drained of their moisture, the tropical air masses reach the Canadian Prairies as aChinook wind or simply "a Chinook", a term which is also synonymous on the Coast with the Pineapple Express.The
San Francisco Bay Area is another locale along the Pacific Coast which is occasionally affected by a Pineapple Express. When it visits, the heavy, persistent rainfall typically causes flooding of local streams as well as urban flooding. In the decades before about 1980, the local term for a Pineapple Express was "Hawaiian Storm". [ "Weather of the San Francisco Bay Region", by Harold Gilliam, published 1962, rev.2002, University of California Press, Berkeley. ] During the second week of January, 1952, a series of "Hawaiian" storms swept into Central California, causing widespread flooding around the Bay Area. The same storms brought a blizzard of heavy, wet snow to the Sierra Nevada Mountains, notoriously stranding the streamlinerCity of San Francisco onJanuary 13 . The greatest flooding in Northern California since the 1800s occurred in 1955 as a result of a series of Hawaiian storms, with the greatest damage in theSacramento Valley around Yuba City.References
ee also
*
Chinook wind
*Siberian Express
*Pacific Organized Track System External links
* [http://www.weathernotebook.org/transcripts/2001/01/17.html Pineapple Express] from a website of the
Mount Washington Observatory
* [http://zebu.uoregon.edu/humid.html Satellite photo of the Pineapple Express] from aUniversity of Oregon website
* [http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17031 Animation of the Pineapple Express] by NASA.
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