My first experience with Stone fly hatches as a fly tier came about in Western Washington along the upper East fork of the Satsop River on the Olympic Peninsula. Daryl, a good friend from Mountain Home Idaho and I were exploring a section of the Satsop that we could only seem to find on the map. It seemed that the river narrowed considerably and wound its way through some older clear cuts, to a point where the springs began to be the main substance of its flow. After being unsuccessful for a couple of hours trying to pick up the stream, we picked an old overgrown logging trail, and headed out on a compass heading that "should" eventually intersect us with the stream.
Looking at the Sapsop Stone, I see a Stonefly pattern that, will be effective on any type of water, warm or cold.