St. Charles in Summer
In summer (June, July and August), St. Charles sees average daytime highs around 80°F and overnight lows near 62°F, with 11.5 in of rain over about 34 wet days across the season. It is the warmest season of the year and the 2nd-wettest season.
Over the season highs climb from about 75°F in early June to 79°F by late August. The sky is clear or mostly clear about 32% of the time across summer, and the air most often feels muggy.
Summer is St. Charles's best season of the year to visit on our travel score. For the whole year in context, see St. Charles's year-round climate.
- Avg daytime high
- 80°F
- warmest season of the year
- Avg overnight low
- 62°F
- Rainfall
- 11.5 in
- 34 wet days
- Avg wind
- 6 mph
- Travel score
- 6.3
- best season of the year
- Months
- Jun · Jul · Aug
Temperature in St. Charles in Summer
Over the season highs climb from about 75°F in early June to 79°F by late August.
A typical summer day in St. Charles reaches about 80°F and drops to 62°F overnight. The warmest of the three months is July, the coolest June.
How summer really feels in St. Charles
Once humidity and wind are folded in, summer brings about 0 days that feel above 90°F and 0 that feel at or below 32°F.
summer sits comfortably in between — no days that feel dangerously hot or drop to a hard freeze once humidity and wind are folded in.
St. Charles weather by month
How the three summer months (June, July and August) compare with the rest of the year — the season's months are highlighted.
| Month | High / Low (°F) | Rainfall (inches) | Wet days | Snow days | Daylight (hours) | Travel score |
|---|---|---|---|---|---|---|
| Jan | 30° / 16° | 2.1 | 7.9 | 5.7 | 9.3 | 0.0 |
| Feb | 34° / 20° | 1.9 | 7 | 4.9 | 10.3 | 0.0 |
| Mar | 46° / 29° | 2.6 | 9.6 | 3.1 | 11.7 | 1.4 |
| Apr | 58° / 39° | 4.5 | 12 | 1 | 13.1 | 4.1 |
| May | 69° / 50° | 4.6 | 12.5 | 0 | 14.3 | 6.0 |
| Jun | 79° / 60° | 4.2 | 12.3 | 0 | 15 | 6.3 |
| Jul | 82° / 65° | 3.7 | 11.2 | 0 | 14.7 | 6.1 |
| Aug | 80° / 62° | 3.7 | 10.6 | 0 | 13.7 | 6.5 |
| Sep | 74° / 55° | 3.1 | 8.4 | 0 | 12.3 | 7.1 |
| Oct | 61° / 43° | 3.1 | 9 | 0.2 | 10.9 | 5.2 |
| Nov | 47° / 32° | 2.4 | 8 | 1.5 | 9.6 | 1.5 |
| Dec | 35° / 22° | 2.2 | 8 | 4.4 | 9 | 0.0 |
Cloud cover in Summer
The sky is clear or mostly clear about 32% of the time across summer.
Chance of precipitation in Summer
St. Charles gets around 11.5 in of rain over 34 wet days across summer. The line is the day-by-day chance of measurable precipitation.
Humidity in Summer
Most of summer feels muggy — the stacked bands show each day's mix of comfort levels, read off the dew point.
Wind in Summer
Winds average 6 mph across summer.
Sunrise & sunset in Summer
Daylight runs from about 14 h 48 min in early June to 13 hours by late August. The lit band spans sunrise to sunset each day.
Solar energy in Summer
Average shortwave solar energy reaching the ground each day across summer, about 6.0 kWh/m².
Is summer a good time to visit St. Charles?
Our two travel scores rate summer for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal), averaged across the three months.
summer is a reasonable time to visit St. Charles for sightseeing. The water and warmth also suit a beach or pool day.
What to pack for St. Charles in Summer
From summer's temperature range, rain chance, sun and wind — what's worth putting in the bag.
In summer, St. Charles sees daytime highs around 80°F and nights near 62°F. Pack light clothes and sun protection. Worth having: rain gear. About 34 days see rain.
Sea temperature near St. Charles in Summer
The nearest coast averages about 67°F across summer — the other half of the beach question. The full-year curve and swim-comfort zones are below.
The sea at the nearest coast (about 35 mi away) is warmest in August at about 73°F and coldest in February near 36°F.
It's comfortable for a long swim from Jul 13 to Sep 15 — about 2.1 months when the water holds above 68°F.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sea temperature (°F) | 38 | 36 | 36 | 39 | 45 | 57 | 70 | 73 | 68 | 58 | 49 | 42 |
| Comfort | Bracing | Bracing | Bracing | Bracing | Bracing | Bracing | Refreshing | Refreshing | Refreshing | Bracing | Bracing | Bracing |
| Sea temperature (°F) | Comfort | |
|---|---|---|
| Jan | 38 | Bracing |
| Feb | 36 | Bracing |
| Mar | 36 | Bracing |
| Apr | 39 | Bracing |
| May | 45 | Bracing |
| Jun | 57 | Bracing |
| Jul | 70 | Refreshing |
| Aug | 73 | Refreshing |
| Sep | 68 | Refreshing |
| Oct | 58 | Bracing |
| Nov | 49 | Bracing |
| Dec | 42 | Bracing |
UV index in St. Charles in Summer
Clear-sky midday UV across summer averages around 8 (very high — sun protection essential). The full-year curve, shaded by WHO exposure level, is below.
Under clear skies, the midday UV index in St. Charles peaks around June 20 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 21 at about 2 (low).
The index reaches 3 or more — the level where the WHO recommends sun protection — in 8 months of the year.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV index (midday) | 2 | 3 | 4 | 6 | 8 | 9 | 8 | 8 | 6 | 3 | 2 | 2 |
| Level | Low | Moderate | Moderate | High | Very high | Very high | Very high | Very high | High | Moderate | Moderate | Low |
| UV index (midday) | Level | |
|---|---|---|
| Jan | 2 | Low |
| Feb | 3 | Moderate |
| Mar | 4 | Moderate |
| Apr | 6 | High |
| May | 8 | Very high |
| Jun | 9 | Very high |
| Jul | 8 | Very high |
| Aug | 8 | Very high |
| Sep | 6 | High |
| Oct | 3 | Moderate |
| Nov | 2 | Moderate |
| Dec | 2 | Low |
Air quality in St. Charles in Summer
Average fine-particle pollution (PM2.5) through the year — so you can see where summer falls, not just the annual average.
Air quality in St. Charles is worst in July — around 17 µg/m³ PM2.5 (moderate), about 1.9× the cleanest month (October, 9 µg/m³).
Modeled monthly averages (CAMS reanalysis, 2015–2024).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| PM2.5 (µg/m³) | 12 | 15 | 16 | 14 | 15 | 16 | 17 | 16 | 13 | 9 | 10 | 11 |
| Level | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Good | Good | Good |
| PM2.5 (µg/m³) | Level | |
|---|---|---|
| Jan | 12 | Moderate |
| Feb | 15 | Moderate |
| Mar | 16 | Moderate |
| Apr | 14 | Moderate |
| May | 15 | Moderate |
| Jun | 16 | Moderate |
| Jul | 17 | Moderate |
| Aug | 16 | Moderate |
| Sep | 13 | Moderate |
| Oct | 9 | Good |
| Nov | 10 | Good |
| Dec | 11 | Good |
Where is St. Charles?
St. Charles sits at 41.9°N, 88.3°W, 732 ft above sea level, in United States. The nearest listed city is Geneva, 1.9 mi away.
Topography around St. Charles
How much the land rises and falls, and what covers it, within 2, 10 and 50 miles of St. Charles.
Within 2 miles, the terrain around St. Charles has only modest variations in elevation — a maximum elevation change of 187 ft around an average of 758 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 430 ft; within 50 miles, significant variations in elevation — a maximum elevation change of 892 ft.
The land around St. Charles is covered by trees (49%) and artificial surfaces (30%) within 2 miles, trees (33%) and grassland (27%) within 10 miles, and cropland (43%) and trees (20%) within 50 miles.
United States travel facts
- Power plugs
- Type A / B
- 120 V · 60 Hz
- Prices
- ≈ 100% of US
- price level, 2025
- GDP per capita
- $90,027
- 2025
- Happiness
- 6.8 / 10
- World Happiness, 2025
- Safe drinking water
- 98%
- of population, 2024
- Homicide rate
- 5.8
- per 100k, 2023
- Road deaths
- 12.7
- per 100k/yr, 2019
- Income group
- High
- World Bank
- Religion
Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.
Data sources
Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for St. Charles (41.9142°, -88.3087°, elevation 732 ft), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google.