Storms could drop a summer’s worth of rain in parts of Texas this week, threatening significant flooding

By Meteorologist Chris Dolce, CNN

(CNN) — Slow-moving storms could drop a summer’s worth of rain over parts of Texas this week, bringing a significant flash flood threat to the state.

Much of eastern, central and southwestern Texas could see downpours heavy enough to trigger flash flooding through Thursday, but the area at greatest risk is near the US-Mexico border in the Rio Grande Valley and the southern Edwards Plateau. Austin, Houston and San Antonio are among the larger cities that could see at least localized flash flooding, especially on Monday and Tuesday.

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The Hill Country is also at risk of flooding rain, but the highest totals could stay just southwest of the region. The threat comes just over a year since the devastating Fourth of July floods that killed more than 130 people there, including 25 girls and two teenage counselors at Camp Mystic.

Flood watches have been issued for almost 6 million people in central and southwest Texas including Austin, Del Rio, San Angelo and San Antonio.

Texas Gov. Greg Abbott activated the state’s emergency response on Sunday to make state resources available, including water rescue teams and helicopters, to respond to any flooding that pops up.

“Texans are urged never to drive or walk through flooded roadways, as floodwaters may be deeper and move more rapidly than they appear,” a release from the governor’s office said.

Extreme rainfall events like this are becoming more common as planet-warming pollution pushes temperatures higher because warmer air holds more moisture. Weather systems can then wring that moisture out like a water-laden sponge, yielding heavy and often highly localized downpours.

Fueling this heavy rain threat is abundant Gulf moisture that’s clashing with a stalled front and a pocket of energy in the upper atmosphere. It’s a notorious recipe for generating slow-moving clusters of storms that can unleash rainfall rates of 2 to 4 inches per hour.

However, pinpointing exactly what towns or cities could see the worst flooding impacts is less certain since it depends on where the most persistent storms flare up from day to day.

The forecast

The week’s most serious heavy rain threat is expected in southwest Texas from near Interstate 10 to the Rio Grande River along the Mexico border, including Del Rio, Texas.

A Level 3 of 4 flash flood risk has been issued through Wednesday by the Weather Prediction Center. Rain in this area on Monday is expected to intensify in the late evening and continue overnight.

Rainfall totals in this area could reach 2 to 6 inches, with locally higher amounts up to 10 inches possible. The higher-end of that range would be close to what Del Rio typically sees from June to August, falling in just a few days.

The Hill Country could see 1 to 3 inches of rain, with locally higher totals possible. The region is prone to flooding because of steep slopes, shallow soils and exposed bedrock that repel heavy rain instead of it allowing it to soak into the ground.

The flood threat could finally ease by Friday or Saturday, but some lingering pockets of showers and storms will remain possible, especially in West Texas.

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