Credit: Eric Gay/AP
A deluge of rain impacted San Antonio, Texas this morning. Above is a picture that was taken of roads that were covered with feet of water. Authorities say at least one person was killed after being trapped in car due to the rising waters.
The amount of rain that fell is impressive. The rain started just before 3AM and continued until Noon. For at least five hours, there were rainfall rates of at least 1” per hour. As you can see by the weather observations below, in the 1 hour precipitation column, San Antonio recorded a soaking 3.88” of rain in only one hour at the 7 AM report.
San Antonio recorded a record-breaking 9.87” that morning for May 25th. That blows the old record of 1.66” out of the water set back in 1933. When you factor in a few inches that fell late in the day on Friday, in a 24 hour timespan ending at 11AM, the city had received over a foot of rain. The sewer system in the city couldn’t handle those kinds of rain amounts in such a short amount of time. Dozens of roads in the city were closed due to flooding. Nearly a hundred people had to be rescued from the flood waters. This will go down in the record books as the wettest day in May on record for San Antonio. The previous number one was 6.82” set on May 31st, 1937. It also happens to be the second wettest day ever on record in San Antonio. The old record set back in 1998 was over 11” of water.
All this water led to a quick rise of the San Antonio River. As you can see below it rose around 30 feet in about four hours to a record crest of 34.21’. The river has since receded.
So how did so much rain fell? Well, there was a very moist airmass in place over southern Texas. A very weak frontal boundary sparked a cluster of heavy rain and thunderstorms over San Antonio. Unfortunately, this area of rain didn’t really move. Rain kept filling in over the same areas leading to such impressive rainfall amounts in the area. This is called “training.” It happens when you don’t have stronger winds aloft to keep thunderstorms on the move. That was definitely the case this morning in Texas.