| Month | High | Low | Rain | Wet days | Score |
|---|---|---|---|---|---|
| January | 4.2° | -5.6° | 69.4mm | 7.3 | 23 |
| February | 7.3° | -3.7° | 63.4mm | 7 | 37 |
| March | 13.2° | 1.2° | 98.6mm | 9.8 | 57 |
| April | 19.2° | 6.6° | 121mm | 10.1 | 77 |
| May | 24.3° | 12.7° | 145.3mm | 11.7 | 77 |
| June | 29° | 18° | 110.9mm | 9.2 | 74 |
| July | 30.8° | 19.8° | 124.2mm | 8.4 | 68 |
| August | 30.4° | 18.9° | 98.6mm | 7.5 | 71 |
| September | 27.2° | 14.3° | 76mm | 6.6 | 86 |
| October | 20.6° | 7.7° | 87.9mm | 8 | 84 |
| November | 13° | 1.5° | 80.1mm | 7.3 | 62 |
| December | 6.8° | -3.1° | 72.1mm | 7.4 | 35 |
January in Saint Charles averages a daily high of 4.2°C with nights around -5.6°C. Expect roughly 7.3 wet days totalling 69.4mm. A hard month to visit for comfort alone.
February in Saint Charles averages a daily high of 7.3°C with nights around -3.7°C. Expect roughly 7 wet days totalling 63.4mm. Demanding conditions — pack for it and plan indoor options.
March in Saint Charles averages a daily high of 13.2°C with nights around 1.2°C. Expect roughly 9.8 wet days totalling 98.6mm. Generally workable, with some weather to plan around.
April in Saint Charles averages a daily high of 19.2°C with nights around 6.6°C. Expect roughly 10.1 wet days totalling 121mm. Comfortable conditions for being outdoors all day.
May in Saint Charles averages a daily high of 24.3°C with nights around 12.7°C. Expect roughly 11.7 wet days totalling 145.3mm. Comfortable conditions for being outdoors all day.
June in Saint Charles averages a daily high of 29°C with nights around 18°C. Expect roughly 9.2 wet days totalling 110.9mm. Generally workable, with some weather to plan around.
July in Saint Charles averages a daily high of 30.8°C with nights around 19.8°C. Expect roughly 8.4 wet days totalling 124.2mm. Generally workable, with some weather to plan around.
August in Saint Charles averages a daily high of 30.4°C with nights around 18.9°C. Expect roughly 7.5 wet days totalling 98.6mm. Generally workable, with some weather to plan around.
September in Saint Charles averages a daily high of 27.2°C with nights around 14.3°C. Expect roughly 6.6 wet days totalling 76mm. Comfortable conditions for being outdoors all day.
October in Saint Charles averages a daily high of 20.6°C with nights around 7.7°C. Expect roughly 8 wet days totalling 87.9mm. Comfortable conditions for being outdoors all day.
November in Saint Charles averages a daily high of 13°C with nights around 1.5°C. Expect roughly 7.3 wet days totalling 80.1mm. Generally workable, with some weather to plan around.
December in Saint Charles averages a daily high of 6.8°C with nights around -3.1°C. Expect roughly 7.4 wet days totalling 72.1mm. Demanding conditions — pack for it and plan indoor options.
Each month scores out of 100. It starts at 100 and loses points for daytime highs outside a 20–27°C band, for wet days, and for nights below 2°C. Nothing else is weighted in — no crowd data, no prices, no opinion. Saint Charles peaks at 86.
Based on 30 years of records, September–October scores highest for comfort in Saint Charles, balancing daytime temperature against rainfall.
July is the warmest, averaging a daily high of 30.8°C.
May is the wettest, averaging 145.3mm of rain across roughly 11.7 wet days.
January is the coolest month, with average daily highs around 4.2°C.