St. Charles, MO climate
St. Charles has chilly winters and warm summers. A typical July afternoon reaches 88°, a January night drops to 22°, and about 9 inches of snow falls in a normal winter.
NOAA 1991-2020 climate normals Updated once a decadeWhat a year in St. Charles feels like
Winter
Spring
Summer
Fall
St. Charles weather by month
Average highs, lows, rain and snow for every month, from NOAA’s 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | 30-yr range |
|---|---|---|---|---|---|---|
| January | 39° | 22° | 2.5" | 4.3" | 8 | 25° – 42° |
| February | 45° | 26° | 2.2" | 2.6" | 7 | 25° – 45° |
| March | 56° | 35° | 3.5" | 0.5" | 10 | 38° – 58° |
| April | 67° | 45° | 4.7" | 0 | 10 | 49° – 62° |
| May | 76° | 55° | 5.0" | 0 | 11 | 61° – 74° |
| June | 85° | 65° | 4.5" | 0 | 9 | 70° – 79° |
| July | 88° | 69° | 3.8" | 0 | 8 | 73° – 85° |
| August | 87° | 66° | 3.6" | 0 | 7 | 71° – 83° |
| September | 80° | 58° | 3.3" | 0 | 7 | 65° – 76° |
| October | 69° | 47° | 3.1" | 0 | 8 | 52° – 64° |
| November | 55° | 36° | 3.4" | 0.1" | 8 | 38° – 53° |
| December | 44° | 27° | 2.6" | 1.5" | 7 | 22° – 44° |
| Year | 66° | 46° | 42.1" | 9.0" | 101 |
“Wet days” have at least 0.01" of rain or melted snow. “Snow on ground” counts days with 1" or more. The 30-year range is the coldest and warmest that month’s average temperature got between 1991 and 2020.
Rain and snow in St. Charles
St. Charles gets 42 inches of rain and melted snow a year. May is the wettest month and February the driest. Rain or snow falls on about 101 days a year.
About 203 frost-free days a year
In half of years the last 32° night comes by April 8 and the first one by October 29. That leaves about 203 frost-free days for gardens, longer than 74% of U.S. towns.
Heating and cooling a home in St. Charles
Engineers use “degree days” to estimate how hard a furnace or air conditioner works. In St. Charles, 78% of that work is heating and 22% is cooling.
Degree days measure how far each day’s average temperature falls below or rises above 65°, added up over a year. Source: NOAA station normals.
St. Charles and its neighbors
St. Charles borders 2 towns with climate data. January nights across them vary by 0.5°. St. Peters has both the coldest January nights (22°) and the hottest July afternoons (89°). St. Charles’s January low is 22° and its July high 88°.
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value.
How St. Charles compares
Compared with every U.S. town and city on TownTapestry, each counted once.
Warmer than it used to be
The last 30 years in St. Charles averaged 0.8° warmer than the 1900s. The biggest change is in February (+2.1°). The shift is smaller than in 82% of U.S. towns.
Change by month1991–2020 average minus 1901–2000 average, at St. Charles’s spot on NOAA’s grid
How much a month can swing
A normal is an average, and real years wander around it. December swings the most: between 1991 and 2020 its average temperature ranged from 22° to 44°. June is the most reliable, staying within 9°.
Common questions about St. Charles’s climate
What is the coldest month in St. Charles?
January, with a typical high of 39° and a low of 22°.
What is the hottest month in St. Charles?
July, with a typical high of 88° and a low of 69°. About 34 days a year reach 90°.
How much snow does St. Charles get?
About 9 inches in a normal winter, most of it in January.
When is the first frost in St. Charles?
In half of years the first 32° night comes by October 29, and the last spring frost by April 8.
What is the rainiest month in St. Charles?
May, with 5.0 inches of rain and melted snow. The year totals 42 inches.
Temperatures and rainfall come from NOAA’s gridded climate normals for St. Charles itself (about a 3-mile square). Snow, frost dates and day counts come from NOAA’s weather station at St Charles Elm Pt, MO (1 mi) away. Normals are 30-year averages, not a forecast. Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000.