March 3-4, 2017 California tornado outbreak

The March 3-4 Southern California tornado outbreak was the costliest and deadliest tornado outbreak ever recorded, as well as the only major outbreak recorded in Southern California. The most powerful tornado, an EF5, was responsible for the majority of the destruction and deaths as it passed through major population centers all throughout the Los Angeles region. The outbreak began in the morning of March 3rd, when a weak EF0 touched down near Lompoc, and ended during the afternoon of the 4th when the final EF2 tornado dissipated near Prescott, Arizona. It began when a major Pacific storm system passed through possibly the most unstable environment ever recorded for the region, causing the perfect conditions for supercell and tornado formation within the storm system. The damage caused by the outbreak was unprecedented and many areas, particularly in the Los Angeles basin after the great EF5 tornado, will have a very long road of recovery to come.

Meteorological history
During the early morning hours of March 3rd, a major storm system along a cold front moved into Southern California, bringing rainfall and isolated thunderstorms. The thunderstorms increased in frequency under unusually unstable air, and the first supercells formed after sunrise. The supercells gave rise to the first tornadoes of the outbreak, initially weak EF0s and EF1s. However, some even more powerful tornadoes formed while the storm system moved into the Los Angeles and San Diego greater areas. The strongest of the outbreak was an EF5 which, as mentioned before, devastated the Los Angeles greater area and became the most devastating single tornado in history. After that, various weaker tornadoes formed as the outbreak moved into the Inland Empire after sunset, and then into the desert the next morning. The outbreak dissipated over the desert that afternoon, with non-tornadic storms associated with the previous storm system continuing through Arizona, New Mexico, Colorado, and eventually reaching the Midwest.

March 3rd event
The day featured a few powerful tornadoes, including the EF5 that devastated the Los Angeles basin. EF0 tornadoes made up about half of all tornadoes on this day, scattered around coastal Southern California. Several EF1 tornadoes formed around the region as well, with the more powerful tornadoes occurring mainly near the coastal regions. Tornadoes of this day mainly affected areas west and south of the desert, with isolated reports in the Antelope Valley and Victor Valley as well as in Kern County.

March 4th event
The outbreak moved into the desert regions, where the drier air prevented many tornadoes from forming. Only one EF4 was recorded with only a couple others being above EF1. The EF4 struck Lake Havasu City near the Arizona border, causing extensive damage. The desert air contributed to the dissipation of the outbreak that afternoon while the main storms were centered over western Arizona.

Strongest tornadoes
This section includes all EF2+ tornadoes.

Los Angeles Greater Area (3/3/17)
A tornado touched down south of Thousand Oaks at 1:15. It gradually intensified as it moved into Agoura Hills, causing the first reports of damage. The tornado moved through the hills to reach Beverly Hills, which the tornado entered as a powerful EF4. It stayed mainly north of the city and again entered the hills to completely demolish the Hollywood sign. After that was done, the tornado intensified to an EF5 and entered downtown LA. Damage described as "cataclysmic" occurred throughout downtown. The tornado retained EF5 strength as it moved eastward, passing through communities such as Monterey Park, El Monte, and La Puente before finally weakening to an EF4 as it moved into Diamond Bar. The weakening tornado continued through Chino, Eastvale, and Riverside. Once entering Moreno Valley, it had weakened to an EF1. It then dissipated between Moreno Valley and Hemet at 5:41 PM after existing for hours. This tornado was responsible for the large majority of damage and deaths of this outbreak, becoming the single most devastating tornado ever. The areas affected will have a very long road of recovery to come, with countless numbers of buildings needing to be rebuilt, as well as the Hollywood sign.

Lake Havasu City (3/4/17)
Touched down in open desert landscape and entered the heart of Lake Havasu City at peak intensity. It was one of the more destructive tornadoes of the outbreak, with the city almost totally leveled.

Poway (3/3/17)
This tornado touched down east of Encinitas, and moved SE towards Poway. It struck that city at peak strength, causing extreme damage, before moving out into the hills and dissipating.

Santa Ana (3/3/17)
Touched down as a waterspout near Sunset Beach, before moving onshore. The tornado moved into Huntington Beach as it strengthened to an EF1, traveling mainly along Warner Ave. It then traveled into Santa Ana as it intensified to its peak. It traveled through downtown Santa Ana, leveling countless buildings. The tornado started to weaken as it entered the Santa Ana mountains and dissipated over the mountains. It was considered the 2nd-most destructive of the outbreak, after the EF5.

Ladera Ranch (3/3/17)
An evening tornado touched down north of Laguna Beach before moving slowly towards Laguna Niguel and strengthening. It then entered San Juan Capistrano as an EF2 and turned to strike Ladera Ranch at peak. The tornado moved into Mission Viejo and then Coto De Caza, before dissipating after striking Trabuco Canyon.

Victorville (3/3/17)
A supercell formed near Phelan, spawning the only tornado recorded in the Victor Valley during this outbreak. The tornado crossed the I-15 to move into northern Hesperia before turning north to reach downtown Victorville at peak intensity.

Julian (3/4/17)
In the early morning hours of March 4th, a supercell spawned a tornado in the mountains east of the San Diego area. It passed near the town of Julian at near peak intensity before dissipating. The tornado was thin, but strong.

NE of Prescott (3/4/17)
The strongest Arizona tornado of the outbreak as well as the last touched down at 4:32 PM. It was near Prescott all its life, and briefly threatened the city before turning away.