Recent National Weather Service and model consensus forecasts position Seattle’s August 30 high in the mid-60s to low 70s, with most guidance clustering near 65–71 °F, directly supporting the market’s heavy weighting on the 68–71 °F bins. A passing upper-level low has advected cooler marine air across the region, limiting daytime heating under persistent cloud cover and light southerly flow, while the moderating influence of Puget Sound and the Pacific prevents rapid warming. This pattern sits well below the 1991–2020 climatological average high of 74.7 °F for the date. With the event less than 24 hours away and limited model spread expected before final observations, trader probabilities reflect the narrow, well-constrained forecast envelope.