Rainfall totals during the next seven days will range from 4 to 8 inches for most areas, with isolated spots getting over 10 inches.
In the video player above, you can see Klein ISD's Memorial Stadium during last night's downpours.
Klein Collins High School seniors walked with umbrellas in their hands while their loved ones tried to stay dry in the stands.
Some parents said they were scrambling to find ponchos and umbrellas before the ceremony.
"We were running around last minute like everybody else, looking for the same things," said one parent.
Over at Alief ISD, Elsik High School graduates walked across the stage with an umbrella in one hand and giving out fist bumps with the other.
On Friday, seniors at Hastings and Alief high schools will be graduating.
The district said they are closely monitoring Friday's weather. If there is lightning, the ceremony will be moved indoors.
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