**Clear skies and light winds overnight on September 11, 2026, enabled strong radiational cooling across the Toronto area, producing a verified minimum of 12°C at official observing sites.** This value aligns with Environment Canada measurements and sits modestly below the 1991–2020 climatological average low of 14.6°C for the date, reflecting typical early-September conditions under a stable high-pressure regime. Forecast models run in the preceding 48 hours converged on overnight lows in the 11–13°C range, with minimal spread, giving traders high confidence ahead of final data release. A realistic challenge would require a significant revision in the official station record or use of an alternate measurement protocol, both of which are uncommon once preliminary observations are confirmed.