Grand Detour, IL climate
Grand Detour has cold, snowy winters and pleasant summers. A typical July afternoon reaches 84°, a January night drops to 13°, and about 32 inches of snow falls in a normal winter.
NOAA 1991-2020 climate normals Updated once a decadeWhat a year in Grand Detour feels like
Winter
Spring
Summer
Fall
Grand Detour 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 | 29° | 13° | 1.7" | 13.6" | 7 | 12° – 34° |
| February | 34° | 17° | 1.8" | 6.7" | 6 | 12° – 37° |
| March | 47° | 28° | 2.5" | 3.0" | 7 | 29° – 53° |
| April | 61° | 38° | 3.8" | 0.8" | 8 | 40° – 56° |
| May | 72° | 49° | 4.7" | 0 | 10 | 54° – 67° |
| June | 81° | 59° | 5.2" | 0 | 9 | 66° – 74° |
| July | 84° | 62° | 4.1" | 0 | 7 | 67° – 79° |
| August | 82° | 60° | 4.0" | 0 | 7 | 65° – 77° |
| September | 76° | 52° | 3.6" | 0 | 7 | 58° – 69° |
| October | 63° | 41° | 3.0" | 0 | 7 | 47° – 58° |
| November | 47° | 30° | 2.5" | 1.5" | 6 | 30° – 48° |
| December | 35° | 19° | 2.1" | 6.7" | 7 | 13° – 38° |
| Year | 59° | 39° | 38.9" | 32.3" | 88 |
“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 Grand Detour
Grand Detour gets 39 inches of rain and melted snow a year. June is the wettest month and January the driest. Rain or snow falls on about 88 days a year.
About 180 frost-free days a year
In half of years the last 32° night comes by April 21 and the first one by October 19. That leaves about 180 frost-free days for gardens, longer than 53% of U.S. towns.
Heating and cooling a home in Grand Detour
Engineers use “degree days” to estimate how hard a furnace or air conditioner works. In Grand Detour, 88% of that work is heating and 12% is cooling, so the furnace matters far more than the air conditioner.
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.
Grand Detour and its neighbors
Grand Detour borders 5 towns with climate data. January nights across them vary by 0.2°. Pine Creek has the coldest January nights (13°) and Dixon the hottest July afternoons (84°). Grand Detour’s January low is 13° and its July high 84°.
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value.
How Grand Detour 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 Grand Detour averaged 1.2° warmer than the 1900s. The biggest change is in December (+2.6°). The shift is smaller than in 51% of U.S. towns.
Change by month1991–2020 average minus 1901–2000 average, at Grand Detour’s spot on NOAA’s grid
How much a month can swing
A normal is an average, and real years wander around it. February swings the most: between 1991 and 2020 its average temperature ranged from 12° to 37°. June is the most reliable, staying within 8°.
Common questions about Grand Detour’s climate
What is the coldest month in Grand Detour?
January, with a typical high of 29° and a low of 13°.
What is the hottest month in Grand Detour?
July, with a typical high of 84° and a low of 62°. About 11 days a year reach 90°.
How much snow does Grand Detour get?
About 32 inches in a normal winter, most of it in January.
When is the first frost in Grand Detour?
In half of years the first 32° night comes by October 19, and the last spring frost by April 21.
What is the rainiest month in Grand Detour?
June, with 5.2 inches of rain and melted snow. The year totals 39 inches.
Temperatures and rainfall come from NOAA’s gridded climate normals for Grand Detour itself (about a 3-mile square). Snow, frost dates and day counts come from NOAA’s weather station at Oregon, IL (8 mi, snow) and Dixon 1w, IL (7 mi, frost, heat and degree days). Normals are 30-year averages, not a forecast. Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000.