It rains here a good deal. So inevitably you will get caught in it. You might as well be prepared with a rain cover. I purchased the Outdoor Designs Rucksack Rain Cover from Rothrock Outfitters located just down the road from Raystown Lake.
It packs incredibly small in its included stuff sack. It is hard to find a rain cover for day packs. Which is odd, since it rains on day hikes too…
The rain cover has a draw string to adjust to different size packs.I have used this one in the rain for a few hours and it kept everything in my pack dry.
You can find these online from $8 to $15.