- Oct 7 - High minimum temperature 14.7°C. Old record 14.4°C in 1909.
- Oct 7 - High minimum dewpoint 11.1°C. Old record 9.5°C in 2006.
- Oct 7 - High humidex 28.9. Old record 27.1 in 2003.
- Oct 10 - High minimum dewpoint 10.1°C. Old record 8.2°C in 1984.
- Warmest October overall since 1963. However, daily highs were warmest since 2011 and daily lows were warmest since 1994.
- Smokiest October since 1992, with respect to number of hours with smoke in ECCC Archives. Up to Oct 31, the year 2021 is now the 3rd smokiest year on record since 1953 with 265 hours.
- October 2021 tied with 1973 for foggiest October on record since 1953 (with respect to number of days with fog recorded), with 6 days recording fog.
- First week of October (Oct 1 to 7) was 3rd warmest on record, averaging 16.7°C. Warmest were 2011 (17.9°C) and 1914 (17.1°C).
- First week of October tied with 2011 for warmest average daytime highs on record with an average of 25.3°C. Previously, the record was 24.5°C in 1943.
- 7 consecutive days above 20°C tied with 1914, 1943 and 2011 for 3rd most consecutive days above 20°C in October since 1872. Most were 11 days in 1963 and 8 days in 1909 and 2010.
- Tied with 1938, 1953 and 2003 for 3rd most days above 25°C in October, with 4 days. Most were 7 days in 1963 and 6 days in 1943.