page_title: December 2014 North American storm complex
section_title: Meteorological synopsis
hierarchical_section_title: December 2014 North American storm complex / Meteorological synopsis
caption_attribution_description: English: A visualization based on numerical modeling of the atmospheric river event known as Pineapple Express that caused a powerful storm in California on December 11, 2014. (Source: NOAA/ESRL/PSD)
context_page_description: The December 2014 North American storm complex was a powerful winter storm that impacted the West Coast of the United States, beginning on the night of December 10, 2014, resulting in snow, wind, and flood watches. Fueled by the Pineapple Express, an atmospheric river originating in the tropical waters of the Pacific Ocean adjacent to the Hawaiian Islands, the storm was the strongest to affect California since January 2010. The system was also the single most intense storm to impact the West Coast, in terms of minimum low pressure, since a powerful winter storm in January 2008. The National Weather Service classified the storm as a significant threat, and issued 15 warnings and advisories, including a Blizzard Warning for the Northern Sierra Nevada.
context_section_description: Late on November 30, 2014, a weak extratropical disturbance developed at the southern end of a cold front, to the northwest of Midway Island, near the International Date Line. During the next few days, the system slowly developed a circulation and began to organize, while moving westward, behind a system that was already impacting the West Coast. On December 2, the storm system weakened, as it interacted with a much more powerful Aleutian low over the Gulf of Alaska, which steered the system into the northeast Pacific. On December 3, the system slowly began to restrengthen. On December 4, the system stalled off the West Coast, to the south of Alaska, as a ridge of high pressure built up over the northeast Pacific. During the next several days, the system gradually absorbed other incoming storms and began to rapidly intensify, attaining a minimum low pressure of 963 mbar (28.4 inHg) on December 9. As the high pressure system off the coast of California began to break down, the storm system began bearing down on the West Coast. On December 10, the system began to impact California, even though the system was slowly beginning to weaken. Due to the anticipated flooding and other impacts, many schools across California, particularly in Northern and Central California, were closed in advance of the storm. On December 11, the system moved ashore in British Columbia, but then the storm's center of circulation degenerated, and the system's low pressure center split, with the new low pressure center becoming the dominant low off the coast of Northern California, later on December 11. Several hours later, after moving northward, the low pressure center split into 2 again, when the storm began to move ashore in the West Coast. The massive winter storm dropped large amounts of rain across California, and the system also brought powerful winds to parts of the state. The ensuing downpour triggered flash floods and power outages across the state. After moving inland, on December 12, the dominant low moved eastward across southwestern Canada, before being absorbed by the new low pressure center over Reno, Nevada, although the storm weakened to a 1004 mbar system in the process. On the same day, the system spawned an EF0 tornado 5 miles from downtown Los Angeles, California, which was the first tornado that Los Angeles had experienced in 10 years. On December 13, the system continued moving eastward, and finally left the West Coast region.
  On the same day, the storm's circulation split for the second time, with the main circulation heading southeastward over Arizona, as the system continued to weaken. During the next day, the storm's center of circulation moved northeastward over the Southwestern United States, before reaching the Central United States on December 14. On December 15, the storm moved into the Midwest region and began to re-intensify, developing an organized center of circulation to the southwest of the Great Lakes. Late on December 15, the winter storm's outer rainbands began impacting the states in the Eastern United States to the west of the Appalachian Mountains. On December 16, the winter storm's center of circulation reached the Great lakes, and the system began dropping rain and snow in New England. The system also began to produce lake-effect snow in the Great Lakes region, and in parts of New England. On December 17, the system developed a secondary low over New Jersey, at the end of an occluded front, even as the main circulation continued to slowly move eastward. Later on the same day, the system's main circulation briefly stalled just north of New York, while the secondary low continued to develop offshore. Late on December 17, the storm system's frontal band exited the New England, even as the secondary low became the dominant low in the system, to the east of Maine. However, the main circulation continued to persist to the east of the Great Lakes, continuing to drop lake-effect snow across New England. On December 18, the secondary low fully absorbed the original low, and the system developed into a well-defin
caption: Wind and Vapor imagery based on numerical modeling of the Pineapple Express that fueled the storm, on December 11, 2014
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