**Cooler air advection behind a cold front, combined with persistent westerly winds and cloud cover from scattered showers, is keeping overnight lows in Toronto tightly clustered around the 15–17 °C range for August 23.** Official model guidance from sources tracking Toronto Pearson shows daytime highs near 20–22 °C under partly cloudy skies with a 60–80 % rain chance, followed by clearing that allows moderate radiational cooling but is limited by 10–15 mph winds. This setup produces forecast minimums mostly between 14–16 °C, explaining why markets price 15 °C, 16 °C, and 17 °C each near 26.5 % while the broader “20 °C or higher” and “10 °C or below” buckets sit close to 40 %—reflecting residual uncertainty in exact clearing timing and boundary-layer mixing. Historical August 23 lows average 17.1 °C, so the current pattern represents a modest negative anomaly driven by the post-frontal regime rather than any extreme Arctic outbreak. Updated model runs and evening observations will be the next key data points before resolution.