anything could happen, it's the weather afterall, but it should be fishable b/c they are not predicting a large amount of rain. the light rain showers will be spread out over multiple days.
Bring a wading staff. It will probably be around 500-600 cfs.
Are you a member of the LJRA? http://www.littlejuniata.org/
You can sign up on line and pick up your hat, sticker at the clean up.