Alton, Illinois Climate by Month
Alton, Illinois, United States
Hot summers and cold winters, with rain spread through the year.
Hot summers and cold winters, with rain spread through the year: that's Alton's climate in short. July is the warmest month, with highs around 88°F (31°C); January is the coolest at 39°F (4°C), and nights dip to 21°F (-6°C). It gets 40 in (1018 mm) of rain a year, spread across the months.
- Warmest month
- 88°F(31°C)
- Average high, July
- Coldest nights
- 21°F(-6°C)
- Average low, January
- Rain per year
- 40 in(1018 mm)
- No clear rainy season
- Humidity
- 70%
- Sunniest: July
Best and worst months in Alton
Best for weatherThe most comfortable weather comes in May, September and October, with highs around 75°F (24°C) and about 3.8 in (96 mm) of rain a month.
Least pleasantDecember and January are the least pleasant; January is the coldest, with highs of only 39°F (4°C).
Comfort combines how close the afternoon high is to 75°F (24°C) with how much rain falls and how humid it is. See where the weather is best in May.
Temperature and rain through the year
Highs and lows (°F)
Average highAverage low
Rain (in per month)
Alton weather by month
| Month | High | Low | Rain | Humidity | Sun |
|---|---|---|---|---|---|
| JanJanuary | 39°F(4°C) | 21°F(-6°C) | 2.1 in(54 mm) | 71% | 1.8 |
| FebFebruary | 44°F(7°C) | 25°F(-4°C) | 2.1 in(54 mm) | 74% | 2.7 |
| MarMarch | 55°F(13°C) | 34°F(1°C) | 3.2 in(82 mm) | 70% | 3.8 |
| AprApril | 67°F(19°C) | 45°F(7°C) | 3.9 in(99 mm) | 66% | 4.7 |
| MayMayBest | 76°F(25°C) | 55°F(13°C) | 4.8 in(121 mm) | 69% | 5.4 |
| JunJune | 84°F(29°C) | 64°F(18°C) | 4.0 in(101 mm) | 69% | 6.2 |
| JulJuly | 88°F(31°C) | 67°F(20°C) | 4.1 in(103 mm) | 71% | 6.2 |
| AugAugust | 87°F(30°C) | 65°F(19°C) | 3.4 in(86 mm) | 72% | 5.6 |
| SepSeptemberBest | 80°F(27°C) | 57°F(14°C) | 3.6 in(92 mm) | 66% | 4.7 |
| OctOctoberBest | 69°F(20°C) | 46°F(8°C) | 2.9 in(74 mm) | 63% | 3.2 |
| NovNovember | 55°F(13°C) | 35°F(2°C) | 3.3 in(83 mm) | 69% | 2.1 |
| DecDecember | 43°F(6°C) | 26°F(-3°C) | 2.7 in(69 mm) | 74% | 1.6 |
1991–2020 averages. Sun is solar radiation in kWh/m² per day. Highlighted: the most comfortable months.
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