The National Weather Service has classified the deadly and damaging storm event in Southeast Texas on Thursday, May 16, as a "derecho."
According to the NWS, a storm is classified as a derecho if the wind damage swath extends more than 240 miles and has wind gusts of at least 58 mph along most of the storm's path.
The storm on Thursday started west of Austin, just to the southeast of San Angelo and traveled roughly 300 miles into Southeast Texas, eventually ending in Chambers County, east of Houston.
It spawned confirmed EF-1 tornadoes in Cypress and Waller County and a track of widespread straight-line wind damage across Houston and Baytown.
The intense wind is also blamed for severely damaged transmission towers and downed power lines causing massive power outages. CenterPoint said nearly a million customers lost power at the height of the storm. That number was under 600,000 by late Friday afternoon.
The powerful storm also killed at least seven people in Houston and Harris County, including a mother of four and a man in the Heights. Both had large trees fall on them. A man in his 70s was killed when a crane fell on his cement truck.
What causes a derecho?
Derechos are associated with bands of rapidly moving showers or thunderstorms variously known as bow echoes, squall lines, or quasi-linear convective systems.
The somewhat rare thunderstorm event can happen in hot, humid weather conditions combined with a strong area of high pressure aloft.
"Although a derecho can produce destruction similar to the strength of tornadoes, the damage typically is directed in one direction along a relatively straight swath," the NWS says. "As a result, the term "straight-line wind damage" sometimes is used to describe derecho damage."
The NWS says derechos are much harder to forecast because of the environment that they thrive in so a progressive derecho can quickly develop with very little warning.