National Weather Service forecasts position Seattle’s June 17 high near 74–75°F under partly sunny skies transitioning to mostly sunny, reflecting rapid moderation from the prior heatwave via strengthening onshore flow and a developing marine layer that caps afternoon warming. This keeps readings close to or slightly above the late-June climatological normal of roughly 70–74°F at Sea-Tac. Model guidance and observational trends show limited potential for 76°F+ without delayed marine intrusion or greater insolation, while downside risk to the low 70s stems from earlier cloud cover or stronger northwest winds. Traders have concentrated probability in the 72–75°F bands, consistent with the narrow forecast envelope and typical intra-day variability in Puget Sound temperature peaks.