**Forecast models and official guidance point to a low in the low-to-mid 50s Fahrenheit for Seattle on September 13, 2026, aligning with the market's leading 54-55°F bin (34.5% implied probability).** Multiple short-range forecasts from September 11 show overnight lows of 52–57°F under overcast skies and light rain or showers associated with a weak frontal system moving through the Pacific Northwest. This keeps temperatures near the 1991–2020 climatological average low of 53.5°F for the date while preventing the stronger radiative cooling that would be needed for readings in the upper 40s or below. Key differentiating factors include the timing and strength of the incoming moisture and southerly flow, which moderate minimum temperatures by limiting clear-sky heat loss and adding cloud cover and light precipitation. Historical extremes (all-time low of 39°F) are far outside current model consensus, explaining the lower weighting on the 47°F-or-below outcome despite its 32.5% share. Conversely, the 66°F-or-higher bin (33.0%) reflects residual uncertainty around how much daytime warmth might linger into the evening or slight forecast shifts, though guidance consistently favors highs in the mid-60s. Traders appear to be balancing the strong consensus around typical early-fall marine-influenced conditions against the inherent variability in exact overnight minima near frontal passages. Updated National Weather Service or high-resolution model runs over the next 24–48 hours will likely narrow the range further as the system’s details become clearer.