The weather is expected to cooperate for the majority of the event, and the slight chance of rain on Sunday is not expected to have much impact. By Thursday, a large high pressure system will be centered over the Great Lakes region, dominating the eastern half of the country. This will provide cool and dry conditions for COTA on Thurday and Friday. The high will shift east on Saturday, and the resulting shift of low level winds to the southeast will start to bring a little more moisture off the Gulf of Mexico. Saturday should have warmer temperatures and a little more cloud cover than Friday.
An upper level trough will move into the Plains on Sunday, along with an associated cold front that will move across Texas. This is not a very strong trough or front, and there won't be a lot of moisture for it to work with, but it could produce a few isolated showers around central Texas on Sunday afternoon. I expect that if there are showers around, they will be light. As a result, I don't think that there should be much impact on the racing.