I have seen this phenomenon only one other time. It was also during the Salmonfly hatch in the Deschutes River Canyon.
The appearance of water bags hanging from the bottom of the cloud occur when heavy rains begin to fall from the cell and then are sucked back up by the intense updrafts. Check out the photo;
PS. The dry fly fishing with Salmonfly patterns was excellent for the last 7 days between Trout Cr. and Maupin. I did two back to back trips through the canyon and everyone's expectations were wildly exceeded. The river is at a perfect level and the fish are all keyed up on eating the big bugs.
