Seattle’s forecast shows a building high-pressure ridge and weakening marine influence driving a warming trend into July 21, with the National Weather Service issuing a heat advisory as temperatures climb from the mid-70s toward the upper 80s or low 90s. Model consensus points to mostly cloudy skies limiting full solar heating, yet reduced onshore flow and urban heat-island effects at Sea-Tac could push afternoon maxima into the 88–93 °F range. Subtle differences among leading brackets hinge on exact cloud timing, boundary-layer mixing, and small spreads between GFS and ECMWF runs; stronger marine push would cap readings near 88–89 °F while clearer conditions favor 90–93 °F. Recent days of above-average warmth have kept trader focus on these narrow thresholds rather than cooler or extreme outcomes.