Seeing a solar eclipse is magnificent regardless of whether or not it is cloudy; however, if the sky is clear of clouds, the sun will be fully visible and thus the experience fully realized.
This dataset shows cloud fraction average in April over a recent ten year period. Cloud fraction is the percentage of each pixel of satellite imagery that is covered in clouds. Looking at a ten year average of cloudiness in October allows us to see what the likelihood is of the solar eclipse occurring on a cloudy day.
Remember, an eclipse is always worth seeing regardless of whether it is a cloudy day or not. Also, this shows the past ten years of clouds in April, not a forecast of clouds for that day. Check the National Weather Service forecast about seven days before for a better idea of what is expected to happen.