Simplify the following text for a Grade 12 native English-speaking person.
Original: Rosa quickly decayed over the mountains of Mexico , and its cloud shield rapidly accelerated northward through the Plains and Mississippi Valley , moistening the atmosphere enough in Texas ahead of a slow moving occluded cyclone to help set the stage for a significant flood event in east Texas on the October 17 .
Simplified: Rosa quickly decayed over the mountains of Mexico , and its cloud shield rapidly accelerated northward through the United States , spreading moisture .