Dallas area hit by flash floods; videos show highway partly underwater

WEATHER NEWS: Dallas area hit by flash floods; videos show highway partly underwater


Flash floods struck the Dallas-Fort Worth area overnight into Monday, with flooded roads requiring rescue efforts as images showed abandoned cars floating down inundated streets. In some areas, the rainfall totals would be considered a 1-in-1,000-year flood.

Rain continues to fall in and around Dallas; some rainfall gauges in the area have recorded more than 10 inches thus far. A record-breaking 3.01 inches of rain was also recorded in one hour at Dallas-Fort Worth International Airport. The National Weather Service in Fort Worth warned of continued risk for “life-threatening flash flooding,” extending its flash flood warning in and around Dallas County until 10 a.m. Central time.

The risk of damage from the floods is “considerable,” it said, warning residents not to drive on flooded roads and to move immediately to higher ground. Flash flood warnings have also been issued for Fort Worth and Canton, Tex.

In some isolated cases, the rainfall would qualify as a 1-in-1,000 interval flood. The downpour marked the latest such flood that has occurred over the past few weeks across the United States. In one week alone, three 1-in-1,000-year rain events occurred — inundating St. Louis, eastern Kentucky and southeastern Illinois. While controversial, the term is used to describe a rainfall event that is expected once in every 1,000 years, meaning it has just a 0.1 percent chance of happening in any given year.

How two 1-in-1,000 year rain events hit the U.S. in two days

Jeff Lindner, a meteorologist for Harris County, Tex., noted on Twitter that one weather gauge recorded nearly 40 percent of its typical annual rainfall in just 12 hours.

Later that morning, that same gauge tallied over 12.6 inches of rain, still within 12 hours.

Water levels at Trinity River at Dallas are expected to enter minor flood stage Monday into Tuesday.

Such rates of precipitation are nearly impossible for soils — not to mention impervious paved surfaces — to absorb without runoff that can cause flash flooding.

The concept of a thousand-year rainstorm is legitimate but limited. Here’s what you should understand about it.

After the flooding rains move out of the Dallas area, they are expecting to continue to track along Interstate 20 toward areas such as Shreveport, La. The National Weather Service’s Weather Prediction Center has issued a moderate risk of excessive rainfall for northeastern Texas and northwestern Louisiana, with 3 to 5 inches of rain expected in the area and rates of 2 to 3 inches per hour possible.

More excessive rain is expected on Tuesday, with the moderate risk for heavy rainfall spreading farther across northern Louisiana into parts of Alabama.

How two 1-in-1,000 year rain events hit the U.S. in two days

Before Monday’s intense rainfall, the Dallas-Fort Worth area was in the midst of a substantial drought. All of Dallas County has been experiencing at least extreme drought for the past three months, according to the U.S. Drought Monitor.

At one point, Dallas had dozens of days above 100 degrees and 67 days in a row without any rainfall, a streak that was finally broken on Aug. 9. Now, in a shocking reversal, it is likely that this August will be Dallas’s wettest since 1899, the Weather Channel’s Jim Cantore noted on Twitter.

The extremely dry ground, along with the rapid rate of rainfall, combined to trigger widespread flooding. Droughts harden topsoils, making it hard for them to absorb heavy precipitation.

Cities across Texas experienced near-record-high temperatures and dryness last month, causing serious precipitation deficits. But the heavy rainfall over parts of the state into Monday may not bring enough relief, the NWS warned.

The heavy rainfall across Texas, Arkansas, Louisiana and Oklahoma stems from an overlap of extreme moisture and a forceful triggering mechanism.

Over the weekend, an underwhelming tropical system moved ashore in northern Tamaulipas, Mexico, with relatively little fanfare. Its direct impacts were minimal, but it trucked ashore an air mass replete with deep tropical moisture. PWATs, or precipitable water indexes — a measure of how much moisture is present in a column of air from the bottom to the top of the atmosphere — are approaching a remarkable three inches.

That’s the air wafting north into thunderstorms and being converted into heavy downpours along a stationary front. The front is draped west to east near the Red River of Oklahoma toward the Arkansas-Louisiana border. A wave of low pressure that is forming along the front and propagating east will further enhance those downpours. Some locations will see a low-end tornado risk, too.

When flooding struck the Dallas area, parts of north-central and northeastern Texas were under flood watches — an alert level that is below flood warnings — until noon Central time Monday, including Dallas, Rockwall and Delta counties. The NWS warned of “rainfall totals of 2 to 5 inches, with isolated amounts in excess of 8 inches.”

Local news outlets and reporters shared videos of a water rescue on a flooded highway in the Dallas area. People swam in murky floodwaters, their vehicles abandoned on roadsides with their alarms blaring.

Matthew Cappucci contributed to this report.

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