| Month | High | Low | Rain | Wet days | Score |
|---|---|---|---|---|---|
| January | -0.9° | -11.6° | 19mm | 6.4 | 17 |
| February | 1.7° | -9.7° | 20.8mm | 6.2 | 18 |
| March | 9.2° | -3.3° | 47.3mm | 8 | 41 |
| April | 16.7° | 2.6° | 78.1mm | 10 | 69 |
| May | 22.8° | 9.4° | 101.4mm | 12.3 | 75 |
| June | 28.5° | 15.4° | 103.7mm | 11.3 | 71 |
| July | 30.2° | 17.7° | 82.5mm | 8.4 | 70 |
| August | 28.8° | 16.3° | 96mm | 9.6 | 74 |
| September | 25.6° | 11° | 69.7mm | 7.5 | 85 |
| October | 17.8° | 3.4° | 55mm | 7.4 | 78 |
| November | 9.3° | -3.6° | 29.6mm | 5.5 | 46 |
| December | 1.5° | -9.3° | 26.2mm | 6.7 | 17 |
January in Sioux City averages a daily high of -0.9°C with nights around -11.6°C. Expect roughly 6.4 wet days totalling 19mm. A hard month to visit for comfort alone.
February in Sioux City averages a daily high of 1.7°C with nights around -9.7°C. Expect roughly 6.2 wet days totalling 20.8mm. A hard month to visit for comfort alone.
March in Sioux City averages a daily high of 9.2°C with nights around -3.3°C. Expect roughly 8 wet days totalling 47.3mm. Demanding conditions — pack for it and plan indoor options.
April in Sioux City averages a daily high of 16.7°C with nights around 2.6°C. Expect roughly 10 wet days totalling 78.1mm. Generally workable, with some weather to plan around.
May in Sioux City averages a daily high of 22.8°C with nights around 9.4°C. Expect roughly 12.3 wet days totalling 101.4mm. Comfortable conditions for being outdoors all day.
June in Sioux City averages a daily high of 28.5°C with nights around 15.4°C. Expect roughly 11.3 wet days totalling 103.7mm. Generally workable, with some weather to plan around.
July in Sioux City averages a daily high of 30.2°C with nights around 17.7°C. Expect roughly 8.4 wet days totalling 82.5mm. Generally workable, with some weather to plan around.
August in Sioux City averages a daily high of 28.8°C with nights around 16.3°C. Expect roughly 9.6 wet days totalling 96mm. Generally workable, with some weather to plan around.
September in Sioux City averages a daily high of 25.6°C with nights around 11°C. Expect roughly 7.5 wet days totalling 69.7mm. Comfortable conditions for being outdoors all day.
October in Sioux City averages a daily high of 17.8°C with nights around 3.4°C. Expect roughly 7.4 wet days totalling 55mm. Comfortable conditions for being outdoors all day.
November in Sioux City averages a daily high of 9.3°C with nights around -3.6°C. Expect roughly 5.5 wet days totalling 29.6mm. Demanding conditions — pack for it and plan indoor options.
December in Sioux City averages a daily high of 1.5°C with nights around -9.3°C. Expect roughly 6.7 wet days totalling 26.2mm. 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. Sioux City peaks at 85.
Based on 30 years of records, September–October scores highest for comfort in Sioux City, balancing daytime temperature against rainfall.
July is the warmest, averaging a daily high of 30.2°C.
June is the wettest, averaging 103.7mm of rain across roughly 11.3 wet days.
January is the coolest month, with average daily highs around -0.9°C.