Recent National Weather Service guidance and ensemble model consensus position a high in the low-to-mid 60s as the most probable outcome for Seattle on September 30, driving the 53% market-implied probability for 64-65°F. A frontal passage on Tuesday brings clearing skies and northerly flow, limiting daytime heating under partly to mostly sunny conditions with light winds and minimal cloud cover. This aligns with climatological norms for late September, where highs average near 66°F but cool slightly behind systems. Shorter-range updates from NOAA and private models show tight clustering around 63-65°F, with limited upside risk to 66-67°F reflected in the 25% odds; cooler scenarios remain possible only if marine influence strengthens unexpectedly. Traders are monitoring the next NWS forecast discussion for any shifts in the steering pattern ahead of resolution.