Best time to visit Alton
The best time to visit Alton is September–October, judged on twenty years of weather records and the events worth going for.
Alton, Illinois, United States
°C
mm
- Average daily high and low
- Precipitation
- Good month
- Best month
- Made good or best by an event
| Month | Average daily high | Average daily low | Precipitation | Verdict |
|---|---|---|---|---|
| January | 3.8 °C / 39 °F | -4.6 °C / 24 °F | 62 mm / 2.4 in | neither best nor good |
| February | 5.9 °C / 43 °F | -3.5 °C / 26 °F | 64 mm / 2.5 in | neither best nor good |
| March | 13.4 °C / 56 °F | 3.4 °C / 38 °F | 102 mm / 4 in | neither best nor good |
| April | 19.1 °C / 66 °F | 8.4 °C / 47 °F | 120 mm / 4.7 in | good month |
| May | 24.3 °C / 76 °F | 14.7 °C / 58 °F | 123 mm / 4.8 in | good month |
| June | 29.4 °C / 85 °F | 19.9 °C / 68 °F | 102 mm / 4 in | neither best nor good |
| July | 30.5 °C / 87 °F | 21.4 °C / 71 °F | 96 mm / 3.8 in | neither best nor good |
| August | 29.7 °C / 85 °F | 20 °C / 68 °F | 82 mm / 3.2 in | neither best nor good |
| September | 26.7 °C / 80 °F | 15.7 °C / 60 °F | 82 mm / 3.2 in | best month |
| October | 19.9 °C / 68 °F | 9 °C / 48 °F | 87 mm / 3.4 in | best month |
| November | 12.5 °C / 55 °F | 2.8 °C / 37 °F | 76 mm / 3 in | neither best nor good |
| December | 6.6 °C / 44 °F | -1.6 °C / 29 °F | 68 mm / 2.7 in | neither best nor good |
Good and best months depend on more than temperature, rain and events. How they are chosen
Each activity on this page has its own good and best months, rated on twenty years of daily weather records. Which measures count, and how much, depends on the activity: humidity for exploring outdoors, wind for the beach, hiking and skiing, snow for skiing alone. Between them, the activities are rated on:
- Daytime highs
- Night-time lows
- How warm it feels
- Humidity
- How much of the day is sunny
- Hours of daylight
- Monthly rainfall
- How many days it rains
- Days of heavy rain
- Wind
- Snowfall and days with snow
- Major events, such as festivals
The chart shows the good and best months for exploring outdoors.
The event icon marks a month that an event lifts to good or best, such as a festival or a natural spectacle. Choose “Weather only” in the toolbar to rate the months on weather alone.
Best months by activity
Exploring outdoors
Mild days and nights, mostly dry and bright. The default for 'when should I go'.
- JJanuary: neither
- FFebruary: neither
- MMarch: neither
- AApril: good
- MMay: good
- JJune: neither
- JJuly: neither
- AAugust: neither
- SSeptember: best
- OOctober: best
- NNovember: neither
- DDecember: neither
- Best
- September–October
- Good
- April–May
Why these months
April · good
In its favour: feels like (high) 17.1 °C / 63 °F, average daily high 19.1 °C / 66 °F, share of daylight that is sunny 69%, precipitation 120 mm / 4.7 in, relative humidity 61%, average daily low 8.4 °C / 47 °F, wet days 11.3 days, days with heavy rain 4.2 days.
May · good
In its favour: feels like (high) 24.6 °C / 76 °F, average daily high 24.3 °C / 76 °F, share of daylight that is sunny 73%, precipitation 123 mm / 4.8 in, average daily low 14.7 °C / 58 °F, relative humidity 67%, days with heavy rain 4.5 days.
Against: wet days 13.4 days.
September · best
In its favour: feels like (high) 27.8 °C / 82 °F, share of daylight that is sunny 82%, average daily high 26.7 °C / 80 °F, precipitation 82 mm / 3.2 in, wet days 7.6 days, days with heavy rain 2.5 days, average daily low 15.7 °C / 60 °F, relative humidity 69%.
October · best
In its favour: feels like (high) 18.1 °C / 65 °F, average daily high 19.9 °C / 68 °F, share of daylight that is sunny 73%, precipitation 87 mm / 3.4 in, wet days 8.3 days, days with heavy rain 3.3 days, average daily low 9 °C / 48 °F, relative humidity 67%.
An activity is listed only where it applies: skiing at ski destinations, beach and swimming at beach destinations. The nearest ski area is Sugar Mountain Resort, 794 km away.
Weather averages
Monthly averages over twenty years, 2006–2025. Highs, lows and precipitation are in the chart at the top.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Feels like (high) | -0.4 °C | 1.9 °C | 10.3 °C | 17.1 °C | 24.6 °C | 31.8 °C | 34.2 °C | 32.8 °C | 27.8 °C | 18.1 °C | 9.3 °C | 3 °C |
| Days with heavy rain | 2.1 days | 2.1 days | 3.9 days | 4.2 days | 4.5 days | 3.5 days | 3.4 days | 3 days | 2.5 days | 3.3 days | 2.5 days | 2.3 days |
| Time rain usually falls | 2 am | 1 am | 10 pm | 7 pm | 11 pm | 7 pm | 5 pm | 3 am | 7 am | 2 pm | 7 am | 2 am |
| Sunshine per day | 6.3 h | 7.4 h | 8.1 h | 9.2 h | 10.5 h | 11.9 h | 12.2 h | 11.6 h | 10.2 h | 8.2 h | 7 h | 5.7 h |
| Relative humidity | 70% | 67% | 65% | 61% | 67% | 67% | 71% | 71% | 69% | 67% | 68% | 73% |
Air quality
Averaged over a shorter period (2022–2025) than the twenty-year averages above, and not counted towards good or best months.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Air pollution (PM2.5) 2022–2025 | 9.2 µg/m³ | 9.9 µg/m³ | 8.4 µg/m³ | 8.8 µg/m³ | 11.4 µg/m³ | 16.2 µg/m³ | 14.7 µg/m³ | 12.1 µg/m³ | 10.3 µg/m³ | 7.1 µg/m³ | 7.7 µg/m³ | 7.8 µg/m³ |
| Air pollution (PM2.5, daily peak) 2022–2025 | 15.4 µg/m³ | 15.8 µg/m³ | 13.9 µg/m³ | 14.7 µg/m³ | 18.3 µg/m³ | 23.8 µg/m³ | 21 µg/m³ | 18.4 µg/m³ | 16.3 µg/m³ | 11.5 µg/m³ | 13.1 µg/m³ | 13.4 µg/m³ |
- Good 15 µg/m³ or less
- Fair 15 to 25 µg/m³
- Moderate 25 to 37.5 µg/m³
- Poor 37.5 to 50 µg/m³
- Very poor 50 to 75 µg/m³
- Extremely poor over 75 µg/m³
Each figure is compared with the World Health Organization's guideline for a day's air, 15 µg/m³ or less, and with its interim targets above that. The words are ours: the WHO does not name its steps. The figures are modelled monthly averages, so single days can be well above them. The daily peak is the average of each day's highest hour, shaded on the same scale.