| Month | High | Low | Rain | Wet days | Score |
|---|---|---|---|---|---|
| January | -3.5° | -9° | 46mm | 16.6 | 0 |
| February | -2.8° | -9.2° | 40.3mm | 13.6 | 3 |
| March | 2° | -6.2° | 32.1mm | 11.6 | 10 |
| April | 8.8° | -0.8° | 30.1mm | 10.1 | 40 |
| May | 16.1° | 4.9° | 45.8mm | 10.3 | 67 |
| June | 20.8° | 10.2° | 62.5mm | 12.1 | 76 |
| July | 23.1° | 13° | 74mm | 13 | 74 |
| August | 21.3° | 11.7° | 65.2mm | 11.6 | 77 |
| September | 15.1° | 7.3° | 52.7mm | 11.2 | 62 |
| October | 8° | 2.6° | 64.6mm | 15.8 | 32 |
| November | 2.5° | -1.4° | 56.3mm | 16.9 | 10 |
| December | -1.4° | -6.1° | 51.5mm | 17.3 | 3 |
January in Lahti averages a daily high of -3.5°C with nights around -9°C. Expect roughly 16.6 wet days totalling 46mm. A hard month to visit for comfort alone.
February in Lahti averages a daily high of -2.8°C with nights around -9.2°C. Expect roughly 13.6 wet days totalling 40.3mm. A hard month to visit for comfort alone.
March in Lahti averages a daily high of 2°C with nights around -6.2°C. Expect roughly 11.6 wet days totalling 32.1mm. A hard month to visit for comfort alone.
April in Lahti averages a daily high of 8.8°C with nights around -0.8°C. Expect roughly 10.1 wet days totalling 30.1mm. Demanding conditions — pack for it and plan indoor options.
May in Lahti averages a daily high of 16.1°C with nights around 4.9°C. Expect roughly 10.3 wet days totalling 45.8mm. Generally workable, with some weather to plan around.
June in Lahti averages a daily high of 20.8°C with nights around 10.2°C. Expect roughly 12.1 wet days totalling 62.5mm. Comfortable conditions for being outdoors all day.
July in Lahti averages a daily high of 23.1°C with nights around 13°C. Expect roughly 13 wet days totalling 74mm. Generally workable, with some weather to plan around.
August in Lahti averages a daily high of 21.3°C with nights around 11.7°C. Expect roughly 11.6 wet days totalling 65.2mm. Comfortable conditions for being outdoors all day.
September in Lahti averages a daily high of 15.1°C with nights around 7.3°C. Expect roughly 11.2 wet days totalling 52.7mm. Generally workable, with some weather to plan around.
October in Lahti averages a daily high of 8°C with nights around 2.6°C. Expect roughly 15.8 wet days totalling 64.6mm. A hard month to visit for comfort alone.
November in Lahti averages a daily high of 2.5°C with nights around -1.4°C. Expect roughly 16.9 wet days totalling 56.3mm. A hard month to visit for comfort alone.
December in Lahti averages a daily high of -1.4°C with nights around -6.1°C. Expect roughly 17.3 wet days totalling 51.5mm. 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. Lahti peaks at 77.
Based on 30 years of records, June–August scores highest for comfort in Lahti, balancing daytime temperature against rainfall.
July is the warmest, averaging a daily high of 23.1°C.
July is the wettest, averaging 74mm of rain across roughly 13 wet days.
January is the coolest month, with average daily highs around -3.5°C.