National Weather Service forecasts and ensemble model runs from GFS and ECMWF currently point to a highest temperature in the low 60s for Seattle on May 17, reflecting a moderating onshore flow from the Pacific that limits daytime heating after the early-May heat wave. Mid-May climatology at Sea-Tac Airport shows average highs clustered in the upper 50s to low 60s, with persistent marine stratus and southwesterly winds often capping peaks several degrees below clear-sky potential. Recent upper-level disturbances have introduced cooler, moist air masses, producing the tight clustering of market-implied probabilities between the 60–63 °F bands while keeping the 64 °F+ outcome at just 22.5 percent. Traders are watching the next HRRR and NAM updates overnight, as any reduction in cloud cover or shift in steering patterns could tip the high into the mid-60s before resolution based on official observations.