Analysis | What made the deadly thunderstorms in Houston so violent? (2024)

The storms that struck Houston were supercells, particularly dangerous rotating thunderstorms that often produce damaging winds and sometimes tornadoes. Several meteorological ingredients, including a link to this week’s record heat in Florida and possibly to an ocean heat wave, led to the storm producing destructive gusts. Radar imagery indicates that winds reached 125 mph just above the ground at skyscraper level, while there were likely gusts of 95 to 115 mph at the surface.

The storms formed along the northern edge of a heat dome centered over Central America and the Caribbean, which have produced record-high temperatures from South Florida to Mexico. Heat domes are large areas of high pressure that stall for days or weeks at a time.

It’s not uncommon for strong thunderstorms to form along the northern periphery of heat domes in what’s known as a “ring of fire” weather pattern. Such storms are fueled by the contrast between the heat dome’s toasty air and cooler air to the north. Infamous violent storm complexes have formed from similar patterns, including in Iowa in 2020 and in the Ohio Valley and Mid-Atlantic in 2012. When these storm complexes produce damage along a sufficiently long path, they are known as derechos. On Friday afternoon, the National Weather Service confirmed Thursday night’s storm complex also qualified as a derecho.

Thursday’s storms were triggered when a zone of low pressure and cold air at high altitudes approached the heat dome from the west, creating a region of ascending air that gave rise to towering clouds and terrifying storms. A combination of sultry air wafting north from the Gulf of Mexico, twisting winds, and a very unstable atmosphere helped make the storms especially intense, according to Hayley Adams, a meteorologist at the National Weather Service office that serves Houston.

Adams also said the presence of drier air at the middle levels of the atmosphere, which can produce a cooling effect that increases the intensity of downward thunderstorm winds that spread outward from the storm when they hit the ground.

“In layman’s terms, there was a lot of parameters that supported the potential for stronger severe storms last night,” Adams said.

The heat dome — which helped provide fuel for the Texas storms — has produced record warmth in South Florida for days, including a heat index near 115 in Key West on Wednesday, around its highest on record. Scores of other high temperature records have been set in South Florida over the past week.

Stretching across the Gulf of Mexico and Caribbean and into Central America, the heat dome has also been responsible for hundreds of heat records from South America to Mexico, where it has intensified extreme drought and fueled wildfires which have sent smoke into the southern United States.

The warm waters of the Gulf of Mexico, which are running 4 to 5 degrees above normal, probably also contributed to the intensity of storms. The world’s oceans have been record-warm for 13 months, according to the World Meteorological Organization.

Human-caused climate change is intensifying the heat over both land and oceans, increasing the likelihood that it’s record-setting. Climate Central’s Climate Shift Index indicates that it made South Florida’s record heat in recent days at least three to four times as probable.

The heat dome fueled Houston’s storms and the low-pressure zone that swept by energized them, but much more localized processes shaped them.

The violent storms were made up of a complex mix of downbursts and tornadoes. Downbursts are pockets of downward-moving air within thunderstorms that splatter outward upon hitting the ground, often causing tornado-like wind speeds. Tornadoes are columns of upward-moving air spiraling inward.

Downbursts and tornadoes can be equally destructive. They can exist very close to each other within severe thunderstorms, making it difficult to distinguish which is responsible for storm damage.

The overall environment was favorable for severe thunderstorms. Storms were moving from west to east along a front draped atop the heat dome while jet stream winds were racing in the same direction overhead. That meant that any storms that grew tall enough could tap into the roaring jet stream winds and bring them down to the ground.

Initially, a layer of cooler air near the ground kept the storms elevated, preventing them from bringing strong winds down to the surface. By the middle of Thursday afternoon, though, a storm cell that formed right along the front was able to stretch from the near the surface to more than 57,000 feet in the air. A healthy inflow of warm, moist air from the Gulf along with spin in the atmosphere allowed the storm to become particularly severe.

Radar imagery indicates that tornadoes formed on the north side of the Houston area shortly after 6 p.m. The Weather Service confirmed a tornado with 110 mph winds in Cypress, in northwest Harris County, where high-voltage electrical transmission towers were toppled.

As the storm moved toward Houston, it began exhibiting continuous rear flank downdraft surges — intense downward bursts of winds that develop as cool air wraps around on a storm’s backside. As they barreled into Houston, they unleashed winds comparable to those from a Category 1 or 2 hurricane. The Weather Service confirmed 100 mph gusts in parts of downtown Houston.

Some of these winds probably strengthened as they funneled between city skyscrapers and are likely responsible for the extreme window damage that occurred. The window damage was reminiscent of Hurricane Alicia in 1983, which also blasted downtown Houston.

Ian Livingston, Jason Samenow and Amudalat Ajasa contributed to this report.