Trader consensus favoring a Seattle high of 74–77°F on August 12 stems from the latest forecast model runs showing a moderate onshore flow off the Pacific that sustains a marine layer of cool, moist air and morning cloud cover. This temperature inversion typically caps afternoon warming near the climatological August average of 77°F, though variable wind speeds and the timing of layer dissipation introduce uncertainty between the two leading bins. Persistent high pressure supports drier conditions consistent with the warmer-than-average summer pattern, but stronger marine influence or delayed clearing could keep readings closer to 74–75°F. Official resolution will hinge on the National Weather Service observation at Sea-Tac, where small shifts in boundary-layer mixing or cloud timing often decide the exact peak.