Preceded by more than a week of heavy rain, a slow-moving storm system dropped tremendous precipitation across much of Texas and Oklahoma during the nights of May 24–26, 2015, triggering record-breaking floods. Additionally, many areas reported tornado activity and lightning. Particularly hard hit were areas along the Blanco River in Hays County, Texas, where entire blocks of homes were leveled. On the morning of May 26, the National Weather Service issued a flash flood emergency for southwest Harris County (which includes the city of Houston) and northeast Fort Bend County. The system also produced deadly tornadoes in parts of Mexico, Texas, and Oklahoma. This flood significantly contributed to the wettest month ever for Texas and Oklahoma.
Meteorological synopsis
According to Bob Henson from Wunderground, inflow of low-level moisture from the Gulf of Mexico and the combination of very slow moving large-scale storm systems set the stage for the floods. He added,"Upper-level winds were largely aligned with the low-level frontal zone, an ideal setup for “thunderstorm training” (successive downpours over the same area). In addition, rains were concentrated by several mesoscale convective vortices, small-scale centers of low-pressure that developed along the frontal bands, in some cases resembling mini-tropical cyclones." The stationary trough during May is linked to both the El Niño and amplified midlatitude short-wave train.
Flooding
On May 14, 2015, prior to extensive flooding beginning around May 24, flash flood warnings were issued for counties in South East Texas. At least 14 people were killed, including 10 in Texas and 4 in Oklahoma, and another 11 remain missing.
Texas
Flooding along the Wichita River prompted evacuations of 390 homes in Wichita Falls. Projections from the National Weather Service indicated that the river would reach a record crest of on May 26. Up to 100,000 customers were without power.
Wichita Falls and Corpus Christi broke their previous records for all-time wettest month. Many parts in northern Texas recorded over of rain.
A 25-foot-by-25-foot sinkhole near a runway at the Dallas/Fort Worth International Airport caused the closure of the runway for a few hours.
Also on May 25, historic flooding along Shoal Creek inundated House Park in Austin, Texas damaging the turf among other things and forcing the Austin Aztex to search for a temporary home.
Houston
More than 500 water rescues were carried out by firefighters, which involved for the most part stranded motorists. At least 2,500 vehicles were abandoned, when drivers had to seek higher grounds.
During the overnight of May 25–26, nearly of rain fell near Houston, setting off further flash floods. Two people drowned after being trapped in their cars while a third was later found in bayou. A fourth person lost their life when an evacuation boat capsized during the morning of May 26. On May 26, Houston Mayor Annise Parker, estimated up to 4,000 properties with significant damage.
Blanco River
During the overnight of May 24–25, more than fell along the watershed of the Blanco River. In just a few short hours, the river rose from roughly to a crest just over , well over the flood-stage, near Wimberley. This broke the river's all-time peak of set in 1929. Tremendous flash flooding ensued as a result, with areas of Hays County being particularly hard hit.
Entire blocks of homes in Wimberley were swept away by a "tidal wave of water" with officials reporting 350–400 residences destroyed in the town alone. For the first time, the river covered portions of Interstate 35, shutting down traffic for hours. Large trees and debris were deposited across the roadway.
One person in San Marcos, Texas was confirmed dead. Thirteen people were carried away when the home they were in was swept downstream. Residents reported seeing it being destroyed after striking a bridge. One occupant was recovered with significant injuries while the other twelve remain missing. At least 1,200 people have been left homeless along the river.
Oklahoma
On May 23, flash flooding along Highway 20 near Claremore claimed the life of a firefighter attempting to rescue people in an apartment complex. He was pulled into a storm drain obscured by the rising waters and carried hundreds of yards away. A fellow firefighter attempting to save him was pulled in as well but managed to escape. The day also saw some roads submerged in as much as of water, and thousands of OG&E customers experienced power outages as a result of the flooding in Oklahoma City and Del City.