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
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 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
Valley
receiving about 9 inches of rain, and some
locations on south and southwest-facing mountain slopes receiving
spectacular totals: San Marcos Pass
, in Santa Barbara County
, received 24.57 inches (624 mm), and Opid's Camp in the San Gabriel
Mountains
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
Sound
region from Olympia, Washington
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 2006
.
Central California, 1952
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". 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
City
.
References
- News: Jet stream unleashed the rains -
OCRegister.com
- Weather of the San Francisco Bay Region, by Harold
Gilliam, published 1962, rev. 2002, University of California Press,
Berkeley.
See also
External links
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