Photo: Keybdn at English Wikipedia · CC BY-SA 3.0Winter nights in St. Charles are colder than in 85% of U.S. towns
The warmest part of a July day comes in at 84° on average. It is a dry place: less rain and snow fall here than on 69% of U.S. towns. The latest 30-year average runs 1.2° warmer than 1901–2000’s, with December up the most. Tender plants can go out after about April 25; in half of years the first frost comes by October 19.
A year in St. Charles at a glance
Each month’s typical high and low, and what it brings.
What stands out about St. Charles’ climate
Compared with towns across the U.S., with St. Charles’ place in Illinois beside it.
What a year in St. Charles feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 174 frost-free days a year
In half of years the last 32° night comes by April 25 and the first by October 19. Frost and day counts come from NOAA’s station at West Chicago Dupage Airport, 3 miles from the town’s center, at about the same height.
The 2023 USDA map puts St. Charles’ center in zone 5b: the coldest night of a typical winter, averaged over 1991–2020, reaches about −11°. Plant labels use the zone; frost dates tell you when to plant.
Freezing nights by month
Average nights at or below 32°
90° days by month
Average days at 90° or more
About 46 inches of snow a winter
Snow, measured at St. Charles 0.1 E, IL, falls mostly in February. Precipitation (rain plus melted snow) adds up to 38 inches a year; May is the wettest month and January the driest. Rain or snow falls on about 129 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in St. Charles
89% of the work is heating, so the furnace matters far more than the air conditioner. Months averaging under 55° run from October through April.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at West Chicago Dupage Airport.
Living with St. Charles’ climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
174 frost-free days in zone 5b. The last frost comes by Apr 25 in half of years, so many gardeners wait a week or two past that to set out tomatoes. The first fall frost comes by Oct 19.
Months with highs of 62–84° and lows of 40° or more: May, June, July, August, September and October. 17 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in St. Charles from natural hazards, river flooding is the largest share (51%); heat waves, cold waves, winter storms and ice storms together are 25%. Normals are averages; the hazards page covers the extremes.
Natural hazards →St. Charles and its neighbors
Every town next door is within a degree of St. Charles in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like St. Charles’, farther away
TownRatings’ own comparison of NOAA 1991–2020 normals, not a NOAA product: places of 5,000+ at least 150 miles away, one per state, closest on January low, July high, precipitation and snow.
| Town | Jan. low | July high | Precip. | Snow |
|---|---|---|---|---|
| St. Charles, IL | 15° | 84° | 38" | 46" |
| Southport, NY | 16° | 83° | 36" | 42" |
| Coldwater, MI | 17° | 83° | 39" | 43" |
| Old Forge, PA | 18° | 84° | 40" | 45" |
| Grimes, IA | 13° | 85° | 36" | 38" |
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value. Snow and frost-free days come from the nearest weather station, so neighbors often share them.
Warmer than it used to be
The last 30 years in St. Charles averaged 1.2° warmer than the 1900s. The biggest change is in December (+2.5°).
A smaller shift than in 63% of U.S. towns.
Change by month
The two periods overlap (1991–2000 is in both), which makes the gap a little smaller than it would be between separate periods.
How St. Charles compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with St. Charles’ place among Illinois’.
St. Charles weather by month
Highs, lows and precipitation from NOAA’s grid at St. Charles’ center; snow, wet days and snow on the ground from St. Charles 0.1 E, IL. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | 30-yr range |
|---|---|---|---|---|---|---|
| January | 30° | 15° | 1.7" | 11.2" | 11 | 13° – 34° |
| February | 35° | 18° | 1.8" | 13.0" | 10 | 14° – 38° |
| March | 47° | 28° | 2.3" | 5.0" | 11 | 28° – 52° |
| April | 60° | 37° | 3.8" | 2.9" | 12 | 40° – 55° |
| May | 71° | 48° | 4.8" | 0.0" | 13 | 54° – 66° |
| June | 81° | 58° | 4.4" | 0.0" | 12 | 65° – 74° |
| July | 84° | 63° | 3.8" | 0.0" | 10 | 68° – 80° |
| August | 82° | 61° | 3.9" | 0.0" | 9 | 66° – 78° |
| September | 75° | 53° | 3.3" | 0.0" | 9 | 58° – 69° |
| October | 63° | 41° | 3.4" | 0.2" | 11 | 48° – 58° |
| November | 48° | 31° | 2.5" | 3.7" | 9 | 32° – 48° |
| December | 35° | 21° | 2.0" | 10.2" | 12 | 15° – 38° |
| Year | 59° | 39° | 37.6" | 46.2" | 129 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 14° to 38°. June is the most reliable, staying within 9°.
Where St. Charles’ numbers come from
Normals are 30-year averages, not a forecast. How TownRatings reads climate data →
- Temperatures and precipitation: NOAA’s gridded 1991–2020 normals for the 5 km cell at St. Charles’ center.
- Snow: St. Charles 0.1 E, IL (NOAA station in town).
- Frost, freezing nights, 90° and 100° days, heating and cooling: West Chicago Dupage Airport, 3 miles from the town’s center, at about the same height; the nearest station that passes our checks for distance, height and agreement with the grid.
- Growing zone: USDA Plant Hardiness Zone Map, 2023. USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu/phzm, accessed 8 Oct 2026.
- Then and now: NOAA’s gridded normals for 1901–2000 at the same cell.
- Storms and extremes: FEMA National Risk Index (expected annual losses to buildings).
Common questions about St. Charles’ climate
What is the weather like in St. Charles?
A typical July afternoon reaches 84°, a January night drops to 15°, and about 46 inches of snow falls in a normal winter. Colder January nights than 85% of U.S. towns; cooler July afternoons than 60% of U.S. towns.
How cold does it get in St. Charles in winter?
January nights average 15°. About 134 nights a year reach 32° or below and 9 reach 0° or below. In the coldest January of the last 30 years the month averaged 13°.
How much snow does St. Charles get?
About 46 inches in a normal winter at St. Charles 0.1 E, IL, most of it in February.
How hot does it get in St. Charles?
July, with a typical high of 84° and a low of 63°. About 15 days a year reach 90° (West Chicago Dupage Airport).
When is the first and last frost in St. Charles?
In half of years the last spring frost (32°) comes by April 25 and the first fall frost by October 19, about 174 frost-free days, at West Chicago Dupage Airport.
What growing zone is St. Charles in?
Zone 5b on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about −11°.
What is the best time of year to visit St. Charles?
By one simple rule (highs of 62–84° and lows of 40° or more), May, June, July, August, September and October. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is St. Charles getting warmer?
Yes: 1991–2020 averaged 1.2° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 63% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in St. Charles.
Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000; USDA/PRISM 2023 hardiness zones; FEMA National Risk Index. Today’s forecast: National Weather Service.