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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.

Causes and effects

A Pineapple Express is driven by a strong, southern branch of the Polar jetstream 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 an El Niño episode.

The composition of moisture-laden air, atmospheric dynamics, and orographic enhancement resulting from the passage of this air over the mountain ranges of the western coast of North America causes some of the most torrential rains to occur in the region. In British Columbiamarker 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 a Chinook wind or simply "a Chinook", a term which is also synonymous on the Coast with the Pineapple Express.

Extreme cases

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 the Willamette Valley Flood of 1996.

Southern California, 2005

A Pineapple Express battered Southern California from January 7 through January 11, 2005. This storm was the biggest to hit Southern California since the El Niño of 1998. The storm caused mud slides and flooding, with one desert location just north of Morongo Valleymarker receiving about 9 inches of rain, and some locations on south and southwest-facing mountain slopes receiving spectacular totals: San Marcos Passmarker, in Santa Barbara Countymarker, received 24.57 inches (624 mm), and Opid's Camp in the San Gabriel Mountainsmarker of Los Angeles County was deluged with 31.61 inches (803 mm) of rain in the five day period.

A Pineapple Express system also battered Southern California from February 10 through February 12, 2003.

Alaska, 2006

The unusually intense rain storms that hit south-central Alaska in August 2006 were termed "Pineapple Express" rains locally.

Puget Sound, 2006

The Puget Soundmarker region from Olympia, Washingtonmarker to Vancouver, 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" on November 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 November 2006, the satellite image shows clouds extending from near Hawaii to Washington


See also: Orting, WA Flash Flood of 2006marker.


Central California, 1952

The San Francisco Bay Areamarker 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". 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 streamliner City of San Francisco on January 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 the Sacramento Valley around Yuba Citymarker.

References

  1. News: Jet stream unleashed the rains - OCRegister.com
  2. Weather of the San Francisco Bay Region, by Harold Gilliam, published 1962, rev. 2002, University of California Press, Berkeley.


See also



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