| Month | High | Low | Rain | Wet days | Score |
|---|---|---|---|---|---|
| January | 5.5° | -2.1° | 24.1mm | 10 | 27 |
| February | 9.4° | -2° | 14.8mm | 7.4 | 45 |
| March | 15.1° | 0.6° | 16.2mm | 7.2 | 68 |
| April | 19.5° | 3.5° | 15mm | 6.5 | 85 |
| May | 24.8° | 8° | 18mm | 7 | 86 |
| June | 29° | 11.7° | 15.7mm | 4.7 | 83 |
| July | 34.4° | 14.3° | 3mm | 1.6 | 67 |
| August | 33° | 13.7° | 4.1mm | 2.2 | 72 |
| September | 27.3° | 9° | 7.3mm | 3.2 | 92 |
| October | 19° | 3.9° | 16.3mm | 6.1 | 85 |
| November | 10.3° | -0.1° | 21.3mm | 9.1 | 48 |
| December | 4.9° | -2.6° | 26.3mm | 10.5 | 24 |
January in Tri-Cities averages a daily high of 5.5°C with nights around -2.1°C. Expect roughly 10 wet days totalling 24.1mm. A hard month to visit for comfort alone.
February in Tri-Cities averages a daily high of 9.4°C with nights around -2°C. Expect roughly 7.4 wet days totalling 14.8mm. Demanding conditions — pack for it and plan indoor options.
March in Tri-Cities averages a daily high of 15.1°C with nights around 0.6°C. Expect roughly 7.2 wet days totalling 16.2mm. Generally workable, with some weather to plan around.
April in Tri-Cities averages a daily high of 19.5°C with nights around 3.5°C. Expect roughly 6.5 wet days totalling 15mm. Comfortable conditions for being outdoors all day.
May in Tri-Cities averages a daily high of 24.8°C with nights around 8°C. Expect roughly 7 wet days totalling 18mm. Comfortable conditions for being outdoors all day.
June in Tri-Cities averages a daily high of 29°C with nights around 11.7°C. Expect roughly 4.7 wet days totalling 15.7mm. Comfortable conditions for being outdoors all day.
July in Tri-Cities averages a daily high of 34.4°C with nights around 14.3°C. Rain is rare — about 1.6 wet days and 3mm across the month. Generally workable, with some weather to plan around.
August in Tri-Cities averages a daily high of 33°C with nights around 13.7°C. Rain is rare — about 2.2 wet days and 4.1mm across the month. Generally workable, with some weather to plan around.
September in Tri-Cities averages a daily high of 27.3°C with nights around 9°C. Expect roughly 3.2 wet days totalling 7.3mm. Comfortable conditions for being outdoors all day.
October in Tri-Cities averages a daily high of 19°C with nights around 3.9°C. Expect roughly 6.1 wet days totalling 16.3mm. Comfortable conditions for being outdoors all day.
November in Tri-Cities averages a daily high of 10.3°C with nights around -0.1°C. Expect roughly 9.1 wet days totalling 21.3mm. Demanding conditions — pack for it and plan indoor options.
December in Tri-Cities averages a daily high of 4.9°C with nights around -2.6°C. Expect roughly 10.5 wet days totalling 26.3mm. 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. Tri-Cities peaks at 92.
Based on 30 years of records, April–May scores highest for comfort in Tri-Cities, balancing daytime temperature against rainfall.
July is the warmest, averaging a daily high of 34.4°C.
December is the wettest, averaging 26.3mm of rain across roughly 10.5 wet days.
December is the coolest month, with average daily highs around 4.9°C.