Environment Canada’s latest forecast calls for a Toronto high near 27°C under mainly cloudy skies with a 30-40% chance of showers or thunderstorms, directly explaining why trader consensus clusters tightly on 25–27°C outcomes. Variable cloud cover modulates incoming solar radiation and thus peak surface heating, while any afternoon convection introduces localized cooling through evaporation and reduced insolation—factors that can shift the daily maximum by 1–2°C depending on timing and coverage. Ensemble models show modest spread around this range, with historical August analogs under similar synoptic setups rarely exceeding 28°C when precipitation risk remains elevated. Market-implied odds therefore embed real uncertainty over whether partial clearing allows brief warming spikes or persistent clouds cap readings closer to 25°C, consistent with official station data from Pearson Airport.