Official forecasts from Environment Canada and supporting models indicate a high near 20–21°C for Toronto on October 4, driven by mild southerly flow ahead of an approaching front, with partly cloudy skies and a 40% chance of showers later in the day. This places the market-implied odds for 20°C and 21°C in the lead, consistent with the latest GFS and regional guidance showing temperatures several degrees above the 17.7°C historical average high. Minor model spreads around afternoon maxima and exact timing of cloud cover introduce the observed probability distribution favoring those two outcomes, while cooler or warmer extremes remain low-probability given current steering patterns and limited diurnal range. Updated NHC-adjacent or Environment Canada briefings tomorrow morning represent the key near-term data point for traders.