It's frequently a gamble. Thunderstorms popping up can be hard to predict. At least you can feel pretty sure there will be plenty of water to float...it just may be muddy in your chosen section. I remember one time the water was crystal clear at the takeout. We drove 4 miles upriver to launch and it was chocolate milk there. Hindsight being what it is, had we asked the shuttle driver he would have told us it was muddy upriver. We could then have alterred our plans and gone downriver to float a different stretch and probably stayed ahead of the mud. If it's muddy from a localized storm, that may clear pretty quick (i.e. in a day or so). But, if it is from a heavy rain over a larger region...it may take 2-3 days.
The USGS gauge on the S. Fork spiked a couple or 3 inches the other day...but it is back down to about 2 feet so should be plenty of water but you will have to "read ahead" to look for shoals, ledges etc and watch for the foam lines and pick the good chutes to run. If it goes back up a couple of inches due to a storm or two, you may easily just float over obstacles...but it may be dirtier than desired for good fishing....bring out the spinners...