Traders see Toronto's August 21 daily minimum temperature as highly uncertain, with outcomes clustered tightly between 13–15 °C and no outcome exceeding 37% implied probability. Recent Global Forecast System and Canadian Meteorological Centre runs diverge on the arrival and depth of a cool northeasterly flow behind a weak frontal passage, with differences in boundary-layer mixing, cloud cover, and radiational cooling under clear skies determining whether the low settles near 13 °C or remains closer to 15 °C. Light winds and reduced cloudiness favor stronger overnight cooling toward the lower end of the range, while modest southerly return flow or increased mixing supports the higher values. These near-term meteorological variables, rather than longer-term climate signals, are the dominant drivers of current market sentiment.