Clusters of violent and slow-moving thunderstorms converged on the Houston area Thursday night, unleashing torrential rain and enormous hail. The deluge wrought havoc on the city, spurring floods reminiscent of Hurricane Harvey in some areas.
And the heavy rain threat is not over.
Houston is under a flash flood watch through Saturday night given the potential for at least one to three additional inches of rain on top of the two to five inches which fell Thursday night and two to three inches Tuesday.
“Soils remain saturated from recent rainfall and many bayous, creeks and rivers remain high so any additional rainfall should run off quickly and cause flooding,” the National Weather Service office serving Houston wrote.
Houston is in a slight risk zone for excessive rainfall both Friday and Saturday.
Additional rainfall is not predicted to be as intense as Thursday night’s deluge, but the Weather Service urged residents to “stay put” if extreme rainfall returns: “Do not attempt to travel,” it warned. “Underpasses and low-water crossings will be life-threatening. If caught in a sinking vehicle, get OUT. Bayous will likely exceed banks and structure flooding could be possible.”
By all accounts, Thursday night’s storms in Houston, which have left the region susceptible to more flooding, were wild. “This is probably the most hellacaious” rain I’ve ever heard in my life,” tweeted Matt Lanza, meteorologist for the Houston weather website SpaceCityWeather.com.
The storms left “at least three bayous flowing over the top of their banks, nearly 90,000 residents without power and dozens reportedly trapped for a time in floodwater on Interstate 10,” The Washington Post’s Timothy Bella reported.
On Friday morning, parts of downtown Houston were “impassable after the heavy rains caused the Buffalo Bayou to overflow,” according to Click2Houston. That’s just one of several locations that were inundated, per SpaceCityWeather.com reporting.
Flooding caused numerous school districts, businesses, and area events to be cancelled Friday, including the Houston public school district.
The torrent was unlike Houston’s typical tropical flooding episodes. Much of it was powered by intense supercell thunderstorms, which also unleashed giant hailstones.
The supercells, fed by speedy high-altitude winds, featured powerful updrafts which allowed such enormous hail to form.
“There were many reports of hail, some up to the size of tennis balls in the Houston metro area. The hail did shatter some windows and likely caused a good bit of damage for some folks,” Lanza said in an interview. Some isolated reports of baseball- or even softball-sized hail came in as well.
Big hail is unusual in this region, in part due to its proclivity for tropical rainstorms which tend to have cloud tops closer to the ground (where it’s warmer) and warmer air at high altitudes. In terms of historical incidents of large hail right around Houston, there aren’t many.
The hail onslaught has limited precedent in records dating to 1850 in Harris County, Lanza noted. “There were at least three reports of hail two inches in diameter or larger,” Lanza said. “There have only been 19 reports of hail that large on record in Harris County.”
Houston’s stormy night was the second of the week. As much as six to ten inches of rain fell Tuesday in the region.
Flooding this week has affected not only southeast Texas but also parts of the southern Plains, the South, and Great Lakes.
Flash flood watches currently extend east from Texas through Louisiana and much of Mississippi.
The excessive rains in many parts of the U.S. this week come just as the National Oceanic and Atmospheric Administration released data showing the last 12 months have been the wettest in recorded history for the Lower 48 states.