Recent observational data and model consensus on overnight radiative cooling under mostly clear skies with light northwesterly winds positioned Toronto’s minimum temperature near the long-term September 10 average of 14.8 °C. Traders weigh the precise minimum recorded at official stations against urban heat-island effects and minor variations in dew-point and wind speed that can shift the low by 1–2 °C. With 16 °C, 15 °C, and 9 °C-or-below outcomes clustered near 50 % implied probability, the market captures residual uncertainty in final verified readings versus preliminary reports, as well as the slim chance of stronger cold-air advection not captured in the primary forecast suite.