By Jose Serrano (staff@latinospost.com) | First Posted: May 25, 2015 04:42 PM EDT
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Memorial Day activities across Texas and Oklahoma were canceled after severe storms left at least four people dead, 12 missing, and over 400 homes destroyed.

Flash flood warnings issued over the weekend continued Monday in areas stretching from the Texas-Mexico border to western Tennessee.

More than 1,000 people have been evacuated and three were said to have been killed in the floods, including a 14-year-old boy found in a storm drain and a man from the Texas city of San Marcos who drowned in the Blanco River.

The river rose to 34 feet in a three-hour span Sunday, breaking a record set in 1929 by about 6 feet. The National Weather Service said the river was causing "catastrophic" flooding.

San Marcos - which sits between Austin and San Antonio - issued a statement calling the heavy floods "the most severe in recent memory." Rainfall averages for San Marcos usually land between 3-6 inches, but amounts up to 10 inches were observed over the weekend.

Authorities in Hays County are still looking for 12 missing people, which include two families from the small town of Wimberley, where over 350 homes fell victim to torrential rains and damaging winds. Numerous water rescues were attempted overnight despite pleas from local officials to avoid high risk areas.

In Oklahoma, a state of emergency remained in effect as more than 3 inches of rain fell in Oklahoma City, making May the wettest month ever recorded with over 17 inches.

A Tulsa woman died on Saturday after her car hydroplaned, the state's emergency management spokeswoman told CNN. On Sunday morning, longtime Claremore firefighter Jason Farley drowned while trying to rescue 10 who were stuck inside their homes.

"It's going to be really hard for our department to come together and heal and go forward," said Fire Chief Sean Douglas. "The effects won't be known for a little while."

Severe thunderstorm threats continued into Monday with the most intense threats coming during late afternoon and evening hours. The weather system had already triggered 36 reported tornadoes across the Great Plains in Nebraska, Illinois, Colorado, Kansas, and Iowa.

According to Weather Channel meteorologist Kevin Roth, tornado threats would persist in some areas but would be significantly lower than the weekend.

The American Red Cross is looking for Texas-area volunteers willing to help flood victims. They held an open training Monday morning, but are still accepting applications for their Central Texas Chapter. Anyone looking to donate is encouraged to call 1-800-RED-CROSS, or text REDCROSS to 90999 to make a $10 donation.

The Austin Disaster Relief Network opened a warehouse at the Oak Meadow Baptist Church in southeast Austin to help those affected. Donations made will be distributed to families in the form of gift cards. Tax deductible donations can be made on the non-profit organization's website.

Similarly, the Salvation Army needs financial donations for its mobile feeding unit, which is providing food and hydration for residents of hard hit San Marcos. All proceeds - which go directly to disaster relief - can be made by check or online at salvationarmytexas.org.

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