Typically the hatchery summers start showing as early as mid-April or May with the peak of the run arriving in late June. Most if not all hatchery summer run programs in Wa. are Skamania stock fish and will reflect similar timings.
Water conditions will dictate your success as the river flow fluctuates between high spring run-off and summer low flows. Try to catch the streams on the drop in June for best success. A few cool, overcast days days following some hot, sunny days will stabilize, then reduce, flows and thats the time to "go get 'em" Good Luck!