Considerable to catastrophic flooding is likely to occur over the next two days in places along the U.S. 90 corridor west of San Antonio, according to federal forecasters, who elevated the risk for heavy rain causing flash flooding to the highest possible level through Thursday morning.

Some places could see a staggering 10 to 20 inches of rain, raising particular concerns among National Weather Service forecasters for people vacationing there and who might not be familiar with the flash flood threat. The areas at greatest expected risk included all or parts of Medina, Frio, Uvalde, Kinney, Maverick, Zavala, Val Verde, Edwards, Real and Bandera counties.

The Pecos, Rio Grande, Nueces, Frio, Medina and San Antonio rivers could all flood, forecasters said.

And areas outside of the worst forecast still faced a possible 2 to 6 inches of rain, including Kerr County. The city of Kerrville Police Department on Monday night and Tuesday said it already barricaded some roadways because of high water.

The warnings arrived barely more than one year after flash flooding killed 119 people in Kerr County on the July 4 holiday, when many children were attending summer camp and families packed RV parks and vacation homes. Residents continue to feel intense anxiety when it rains and were watching the forecasts.

Weather experts after last summer’s flood cautioned that it is impossible to predict precisely and with certainty where the heaviest rain might fall. That’s why people need to have a way to receive weather warnings and be aware of how they might need to act.

State legislators have since required certain areas prone to flash-flooding to install warning sirens, a process that is ongoing. The state also mandated new safety standards at youth camps, but it took no action on other recommendations such as standardizing training for local emergency management coordinators.

Gov. Greg Abbott midday Tuesday issued a disaster declaration for 59 counties in recognition of the threat to make resources available.

“Texas is positioned to respond quickly and effectively,” Abbott said in a statement. “I urge all Texans in affected areas to monitor local weather forecasts, avoid driving through flooded roadways, and have emergency supplies ready.”

Storms had already dropped more than 10 inches of rain north of Uvalde as of Tuesday, with more heavy rain also falling in parts of Medina, Bandera and Kerr Counties, according to the National Weather Service Austin and San Antonio Office. The Uvalde County Sheriff’s Office on Tuesday was urging people to stay home and reporting on roadways that had flooded. Bandera and Medina County also reported multiple road closures, including on U.S. 90.

Forecasters expected a lull in storm activity before it ramped up again overnight Tuesday into Wednesday morning.

“All areas are kind of saturated now across the Rio Grande, Edwards Plateau and in portions of the western Hill Country and U.S. 90 corridor,” forecaster Jason Runyen said at an afternoon webinar. “Any additional heavy rainfall that occurs is going to run off very, very quickly.”

This article first appeared on The Texas Tribune.