The near-certain market positioning at 21°C stems from official observational data recorded at Toronto Pearson International Airport on May 16, where the daily maximum reached precisely that value under stable, moderate spring conditions. Environment Canada reports confirmed a daytime peak influenced by a northerly flow that suppressed warmer advection from the south, keeping temperatures within a narrow range consistent with seasonal averages around 18–20°C. Minor model discrepancies in prior forecasts had briefly suggested possible 22°C readings, yet surface measurements and station verification locked in the lower outcome. Only an unreported station anomaly or revised quality-control adjustment could realistically alter resolution, though such revisions remain historically rare for this location and date.