December 2015 North American storm complex

The outbreak was caused by a vigorous upper-level trough that moved into the Central and Southern Plains states on December 25. An extratropical cyclone developed ahead of this upper-level trough over the West Coast, which moved southeast into the Southwestern United States early on December 26. Continuing to move east, snow began to fall in the Upper Midwest, dropping up to 5–8 inches (13–20 cm), before rapidly dissipating.^[5] As the initial low-pressure area moved over the United States–Mexico border, a southwards dip in the jet stream to the west had formed. In response to this, an upper-level low developed by evening on December 26. This upper-level low began to track to the north, drawing moisture from the Pacific Ocean and Gulf of Mexico. As it did so, a long cluster of heavy showers and thunderstorms fired up from eastern Oklahoma to southwestern Missouri, which set up a severe flooding event. Some areas picked up to over 1 inch (25 mm) of rainfall, triggering several floods.^[6]

At the same time, discrete tornadic supercells developed in Texas. One of the cells produced a violent EF4 wedge tornado, which ripped through parts of Garland and Rowlett, Texas, causing major damage and killing 10 people.^[4] As the storm complex began to move to the north, more supercells formed, and several more tornadoes were reported. By the early morning of December 27, the supercells had merged into a squall line, which produced a few more isolated tornadoes.

While generating severe weather in the Deep South, the storm complex brought heavy snow and blizzard conditions in the southwestern parts of Texas through December 26–27, as frigid temperatures had spilled south into the area just the previous day before. Strong winds contributed to power outages and blowing and drifting snow. Snowfall continued throughout December 27 before tapering off near midnight as the storm system began to pull out of the region. In total, the storm complex dumped up to two feet (60 cm) of snow in the western parts of Texas, a very rare and historic occurrence in the affected areas.^[5] The storm had also produced a small but significant ice storm in the central parts of Texas, with ice accumulations ranging up to one inch (25 mm) in some areas, leading to thousands of power outages.^[5]

By December 28, the storm complex had moved into the Central United States, producing more snow, ice, heavy rain, and severe weather in an area stretching from the Midwest into Louisiana. The upper-level low eventually began to take over as the dominant low, and had begun to make a more east-northeastwards turn. Spreading a swath of 6–12 inches (15–30 cm) from Missouri to Maine, the storm complex continued to accelerate into southern Canada while producing more ice, rain and severe weather as the southern quadrant approached the East Coast.^[5] Rain eventually reached areas like Philadelphia and New York City late on December 28, and persisted somewhat into the early morning hours of December 29. At this point, the storm system had already entered Canada, and its circulation was beginning to become elongated. The remnants of the storm eventually dissipated, early on December 30.^[7]

On December 26, 2015, the tornado outbreak portion of the storm system, with 32 tornadoes total confirmed, began when 12 tornadoes impacted Texas that evening, mostly in and around the Dallas–Fort Worth metroplex, killing 13 people,^[46][47][48] which made it the deadliest tornado disaster in the area since the Dallas tornado of 1957, and added to the highest tornado death count in the U.S. for the month of December since 1953.^[49][50] An EF3 tornado moved through multiple subdivisions in Ovilla and Glenn Heights, Texas on the south side of the metroplex, destroying numerous homes and two churches. Ten people in Garland, Texas died as a result of a large and powerful EF4 wedge tornado that also destroyed many homes in the neighboring suburb of Rowlett. An EF2 tornado killed two people in Copeville, while an EF1 caused another fatality near Blue Ridge. Additional tornadoes touched down across the Southern United States on December 27 and 28. Most of these tornadoes were weak, though EF2 tornadoes caused considerable damage near Marianna, Arkansas and Marshall, Texas.^[51] More than 65,000 people lost power in the area due to the tornadoes.^[52][53] The Dallas Mavericks had to delay their NBA game against the Chicago Bulls by one hour due to the threat of severe weather.^[54]

Damage from tornadoes in Texas alone is estimated at $1.2 billion.^[48] There were also 635 injuries.^[a]

The storm system was responsible for heavy rain that caused severe flooding in 13 states, with Missouri being especially impacted.^[55][56] Parts of the state were hit with over 10 in (250 mm) of heavy rainfall.^[46] At least 14 people died due to the floods in Missouri alone.^[57] In Union, Missouri, the Bourbeuse River rose to 34.22 ft (1,043 cm), above the preceding record of 33.79 ft (1,030 cm) which occurred on December 5, 1982.^{[56][58][59][60]} More than 180 roads, including portions of Interstates 44, 55, and 70, and several bridges were closed.^[61][62] The Meramec River, near St. Louis, crested 2 ft (60 cm) above its previous record height, inundating nearby communities. At least 380 homes and 70 businesses were flooded in Franklin County.^[61]

Approximately 140,000 sandbags were brought in to protect portions of the Bayshore subdivision in Arnold. At least 150 homes succumbed to flooding in the city.^[61] More than 100 boat rescues were conducted in Eureka.^[63]

Major flooding also occurred in south Alabama, where the Pea River in Elba, Alabama flooded. Most of the rainfall occurred on Christmas Eve day when training thunderstorms went over the same areas. All in all, a widespread 8–16 inches (200–400 mm) occurred.

Nine levees were topped—five along the Mississippi River, three along the Missouri River, and one along the Kaskaskia River—though the affected areas were predominantly unpopulated.^[63][64] Large stretches of the Mississippi River were placed on alert due to projected major flooding.^[65]

Flash flooding also claimed seven lives in Illinois, two in Oklahoma, one in Arkansas, and one in Georgia.^{[3][47][66][67]}

The combination of heavy snow, strong winds, and bitterly cold temperatures resulted in blizzard conditions across most of New Mexico, southeastern Colorado, western Oklahoma and West Texas. Some places in this area had over 1–3 ft (30–91 cm) of snow but also snow drifts up to 12 feet (370 cm) high.^[68] In the path of this Texas low, a swath of snow and ice impacted the central Plains and Midwest from Oklahoma to Wisconsin as the storm system moved northeastward toward the eastern Great Lakes. The storm system spread a wintry mix of snow, sleet and freezing rain to New York State and New England, disrupting travel in the region. At least 1 person in New Mexico, and 4 people in Oklahoma died as a direct result of the winter storm system.^{[3][47][69][70][71]} Interstate 10 in western Texas was shut down due to the storm, while Midland, Texas experienced their 3rd snowiest day on record.^[72] US 67 was also shut down in portions of Texas from Marfa to Presidio, while US 62 shut down from Carlsbad, New Mexico to the Texas state line.^[73]

More than 750 flights were cancelled at Chicago O'Hare International Airport, and hundreds more at Detroit, Toronto and Montreal. Due to a strong Arctic air mass north of the system, parts of northern Michigan, Ontario and all Quebec suffered blizzard conditions, with moderate snow bands and moderate winds as well. 20–30 cm of snow (8–12 in) fell in Ottawa–Gatineau, less than 10 cm (3.9 in) in Toronto, and the greater Montreal region had 30–40 cm of snow (12–16 in).^{[3][5][46][47][74][75][76][77]}

Four people died in Minnesota in a car accident linked to snow-covered roads.^[78] Two people died from overexertion while clearing snow in Milwaukee, Wisconsin.^[79] Other similar indirect deaths from the winter storm were reported in New Mexico (1 death), Missouri (2), Michigan (1), New York (1), Vermont (3), New Hampshire (1), and Maine (1).^{[3][69][80][81][82]}

The dairy industry in eastern New Mexico and western Texas lost 30,000 cows to the storm.^[83]

• Late December 2012 North American storm complex
• December 2013 North American storm complex
• November 2015 United States ice storm
• Mid-January 2017 North American ice storm
• Tornado outbreak and floods of April 28 – May 1, 2017

• North and Central Texas December 26, 2015 Tornado Outbreak (NWS Fort Worth)