Alton
United States · North America
Year-round range: 25°F to 87°F
September
Excellent conditions this month
Your monthly fit score
Comfort fit by month.
Climate details▼
Temperature
Average highs and lows.
September is warm and sunny — good beach and outdoor weather.
Shaded band = typical daily swing (P10 of night lows to P90 of afternoon peaks) — spans wider than avg high/low lines because it captures day-to-day variation.
| = SepPrecipitation
Monthly precipitation, wet-day risk, and snow signal where relevant.
September has moderate rainfall — occasional showers but mostly manageable.
Sunshine
Average hours of bright sun per day.
September is one of the sunniest months — great for outdoor plans.
Air comfort by month
Humidity and heat feel by month.
September is mostly comfortable — low heat and humidity pressure.
Time-of-day patterns
Typical hourly rhythm for September.
Temperature by hour
Temperature by hour and month
Typical temperature through the day across the year (1996-2025 normals, local time). Shaded cells are nighttime.
In September, afternoons reach about 79° and nights settle near 61°.
▶Full month-by-month data
| Month | High °F | Low °F | Rain days | Rain (in) | Sun h/day | Humidity |
|---|---|---|---|---|---|---|
| Jan | 39°F | 25°F | 7 | 2.6in | 4.5h | 66.71428571428571% |
| Feb | 45°F | 28°F | 7 | 2.4in | 5h | 64.14285714285714% |
| Mar | 57°F | 38°F | 10 | 3.7in | 5.8h | 62.42857142857143% |
| Apr | 67°F | 48°F | 11 | 4.5in | 6.9h | 62.285714285714285% |
| May | 76°F | 58°F | 13 | 4.9in | 7.4h | 65.71428571428571% |
| Jun | 85°F | 68°F | 11 | 4.0in | 8.7h | 65.71428571428571% |
| Jul | 87°F | 71°F | 10 | 3.5in | 9.4h | 68.71428571428571% |
| Aug | 86°F | 70°F | 8 | 2.9in | 9.1h | 67.85714285714285% |
| Sep | 80°F | 62°F | 7 | 3.2in | 8.6h | 65.28571428571428% |
| Oct | 68°F | 52°F | 8 | 3.2in | 7.1h | 64.14285714285714% |
| Nov | 55°F | 40°F | 8 | 3.4in | 5.5h | 66.85714285714285% |
| Dec | 44°F | 31°F | 8 | 2.5in | 4.2h | 70.28571428571428% |