National Weather Service forecasts and ensemble model consensus from the GFS and ECMWF project a daytime high of 58–65 °F at Seattle-Tacoma International Airport on May 18, supported by a gradual shift toward warmer southerly flow and reduced marine-layer cloud cover following the recent cool spell. This places the 58 °F threshold well within the central tendency of guidance, with only modest spread in the afternoon temperature maximum. The 98.9 % market-implied probability aligns with these official runs, which show low risk of a strong onshore surge or persistent stratus that historically caps highs in the mid-50s during mid-May. A realistic challenge would require an unexpected strengthening of the marine layer or a late-model shift toward cooler northerly advection, both of which remain low-probability scenarios within the current 48-hour forecast window.