St. Clair, IL climate
St. Clair has chilly winters and warm summers. A typical July afternoon reaches 89°, a January night drops to 23°, and about 11 inches of snow falls in a normal winter.
NOAA 1991-2020 climate normals Updated once a decadeWhat a year in St. Clair feels like
Winter
Spring
Summer
Fall
St. Clair 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 | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 40° | 23° | 2.6" | 3.4" | 7 | 6 | 26° – 42° |
| February | 45° | 27° | 2.2" | 3.3" | 8 | 2 | 27° – 46° |
| March | 56° | 36° | 3.5" | 1.0" | 10 | 0 | 39° – 59° |
| April | 68° | 45° | 4.9" | 0 | 10 | 0 | 49° – 62° |
| May | 77° | 56° | 5.0" | 0 | 12 | 0 | 61° – 74° |
| June | 85° | 65° | 4.4" | 0 | 9 | 0 | 70° – 79° |
| July | 89° | 68° | 3.9" | 0 | 7 | 0 | 73° – 85° |
| August | 87° | 66° | 3.3" | 0 | 7 | 0 | 71° – 83° |
| September | 81° | 58° | 3.4" | 0 | 7 | 0 | 65° – 75° |
| October | 69° | 47° | 3.2" | 0 | 8 | 0 | 53° – 64° |
| November | 55° | 36° | 3.5" | 0.6" | 8 | 1 | 38° – 53° |
| December | 44° | 28° | 2.7" | 2.9" | 8 | 3 | 22° – 44° |
| Year | 66° | 46° | 42.5" | 11.2" | 100 | 12 |
“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. Clair
St. Clair 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 100 days a year. Snow covers the ground about 12 days of the year.
About 189 frost-free days a year
In half of years the last 32° night comes by April 12 and the first one by October 20. That leaves about 189 frost-free days for gardens, longer than 63% of U.S. towns.
Heating and cooling a home in St. Clair
Engineers use “degree days” to estimate how hard a furnace or air conditioner works. In St. Clair, 73% of that work is heating and 27% 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. Clair and its neighbors
St. Clair borders 9 towns with climate data. January nights across them vary by 0.5°. Shiloh Valley has the coldest January nights (23°) and Smithton the hottest July afternoons (89°). St. Clair’s January low is 23° and its July high 89°.
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value.
How St. Clair 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. Clair averaged 1.1° warmer than the 1900s. The biggest change is in December (+2.2°). The shift is smaller than in 57% of U.S. towns.
Change by month1991–2020 average minus 1901–2000 average, at St. Clair’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. Clair’s climate
What is the coldest month in St. Clair?
January, with a typical high of 40° and a low of 23°.
What is the hottest month in St. Clair?
July, with a typical high of 89° and a low of 68°. About 53 days a year reach 90°.
How much snow does St. Clair get?
About 11 inches in a normal winter, most of it in January.
When is the first frost in St. Clair?
In half of years the first 32° night comes by October 20, and the last spring frost by April 12.
What is the rainiest month in St. Clair?
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. Clair itself (about a 3-mile square). Snow, frost dates and day counts come from NOAA’s weather station at Belleville Siu Rsch, IL (7 mi) away. Normals are 30-year averages, not a forecast. Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000.