| Month | High | Low | Rain | Wet days | Score |
|---|---|---|---|---|---|
| January | 2.3° | -7.7° | 70.3mm | 10.7 | 9 |
| February | 3.7° | -7.2° | 65.8mm | 9 | 16 |
| March | 8.4° | -2.8° | 99.8mm | 10.3 | 35 |
| April | 14.9° | 2.5° | 98.9mm | 12.5 | 59 |
| May | 20.8° | 7.9° | 81.6mm | 12.6 | 75 |
| June | 25.6° | 13.1° | 102.3mm | 13.3 | 73 |
| July | 29° | 16.6° | 97.8mm | 12.5 | 67 |
| August | 28.1° | 15.5° | 92.8mm | 12.1 | 71 |
| September | 23.9° | 11.1° | 87.9mm | 11.9 | 76 |
| October | 17.2° | 4.9° | 106.3mm | 12.1 | 67 |
| November | 11.1° | -0.2° | 86.9mm | 10.3 | 48 |
| December | 5.3° | -4.6° | 101.2mm | 11.3 | 20 |
January in Waltham averages a daily high of 2.3°C with nights around -7.7°C. Expect roughly 10.7 wet days totalling 70.3mm. A hard month to visit for comfort alone.
February in Waltham averages a daily high of 3.7°C with nights around -7.2°C. Expect roughly 9 wet days totalling 65.8mm. A hard month to visit for comfort alone.
March in Waltham averages a daily high of 8.4°C with nights around -2.8°C. Expect roughly 10.3 wet days totalling 99.8mm. Demanding conditions — pack for it and plan indoor options.
April in Waltham averages a daily high of 14.9°C with nights around 2.5°C. Expect roughly 12.5 wet days totalling 98.9mm. Generally workable, with some weather to plan around.
May in Waltham averages a daily high of 20.8°C with nights around 7.9°C. Expect roughly 12.6 wet days totalling 81.6mm. Comfortable conditions for being outdoors all day.
June in Waltham averages a daily high of 25.6°C with nights around 13.1°C. Expect roughly 13.3 wet days totalling 102.3mm. Generally workable, with some weather to plan around.
July in Waltham averages a daily high of 29°C with nights around 16.6°C. Expect roughly 12.5 wet days totalling 97.8mm. Generally workable, with some weather to plan around.
August in Waltham averages a daily high of 28.1°C with nights around 15.5°C. Expect roughly 12.1 wet days totalling 92.8mm. Generally workable, with some weather to plan around.
September in Waltham averages a daily high of 23.9°C with nights around 11.1°C. Expect roughly 11.9 wet days totalling 87.9mm. Comfortable conditions for being outdoors all day.
October in Waltham averages a daily high of 17.2°C with nights around 4.9°C. Expect roughly 12.1 wet days totalling 106.3mm. Generally workable, with some weather to plan around.
November in Waltham averages a daily high of 11.1°C with nights around -0.2°C. Expect roughly 10.3 wet days totalling 86.9mm. Demanding conditions — pack for it and plan indoor options.
December in Waltham averages a daily high of 5.3°C with nights around -4.6°C. Expect roughly 11.3 wet days totalling 101.2mm. A hard month to visit for comfort alone.
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. Waltham peaks at 76.
Based on 30 years of records, May–June scores highest for comfort in Waltham, balancing daytime temperature against rainfall.
July is the warmest, averaging a daily high of 29°C.
October is the wettest, averaging 106.3mm of rain across roughly 12.1 wet days.
January is the coolest month, with average daily highs around 2.3°C.