Pineapple Express
A Pineapple Express is an example of an atmospheric river, which is a more general term for such relatively narrow corridors of enhanced water vapor transport at mid-latitudes around the world.
A Pineapple Express is driven by a strong, southern branch of the polar jet stream and is marked by the presence of a surface frontal boundary which is typically either slow or stationary, with waves of low pressure traveling along its length.
[6] The San Francisco Bay Area is another locale along the Pacific Coast which is occasionally affected by a Pineapple Express.
[7] During the second week of January 1952, a series of "Hawaiian" storms swept into Northern 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 train City of San Francisco on 13 January.
[9] The storm caused mud slides and flooding, with one desert location just north of Morongo Valley receiving about 9 inches (230 mm) 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 Opids Camp (AKA Camp Hi-Hill) in the San Gabriel Mountains of Los Angeles County was deluged with 31.61 inches (803 mm) of rain in the five-day period.
[citation needed] The unusually intense rainstorms that hit south-central Alaska in October 2006 were called "Pineapple Express" rains locally.
[11] The Puget Sound region from Olympia, Washington to Vancouver, British Columbia received several inches of rain per day in November 2006 from a series of successive Pineapple Express related storms that caused massive flooding in all major regional rivers and mudslides which closed the mountain passes.
Portions of Oregon were also affected, including over 14 inches (360 mm) in one day at Lees Camp in the Coast Range, while the normally arid and sheltered Interior of British Columbia received heavy, coastal-magnitude rains.
[12] In December 2014, a powerful winter storm enhanced by a Pineapple Express feature struck California, resulting in snow, wind, and flood watches.
[13] A blizzard warning was issued by the National Weather Service for the Northern Sierra Nevada for the first time in California since October 2009 and January 2008.
[28] Heavy rains attributed to a Pineapple Express event heavily impacted the Puget Sound region from Bellingham, Washington into the British Columbia Interior and the Lower Mainland from 14 to 15 November.
