December 2014 North American storm complex
Satellite image of the system off the coast of California, on December 10, 2014, with the flow of the Pineapple Express marked by the yellow arrow
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| Type |
Extratropical cyclone Bomb cyclone Blizzard Nor'easter Winter storm Tornado outbreak European windstorm |
|---|---|
| Formed | November 30, 2014 |
| Dissipated | December 28, 2014 |
| Lowest pressure | 960 mbar (28 inHg) |
| Tornadoes confirmed | 4 confirmed |
| Max rating1 | EF0 tornado |
| Highest gust | 139 mph (224 km/h) (White Mountain Peak) |
| Maximum snowfall or ice accretion | 14.6 in (37 cm) of rainfall (Petrified Forest) |
| Damage | Unknown |
| Areas affected | Southeast Alaska, Western Canada, Contiguous United States, Great Lakes region, Eastern Canada, Southern Greenland, Iceland, United Kingdom, Ireland, Europe, Western Russia |
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1Most severe tornado damage; see Fujita scale Part of the 2014–15 North American winter |
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1Most severe tornado damage; see Fujita scale
The December 2014 North American storm complex was a powerful winter storm (referred to by some as California's "Storm of the Decade") 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 (the first issued in California since January 2008).
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 EF-0 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.
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