Sullivan, IL climate
Sullivan has chilly winters and warm summers. A typical July afternoon reaches 84°, a January night drops to 17°, and about 28 inches of snow falls in a normal winter.
NOAA 1991-2020 climate normals Updated once a decadeWhat a year in Sullivan feels like
Winter
Spring
Summer
Fall
Sullivan 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 | 32° | 17° | 2.1" | 8.4" | 7 | 13 | 16° – 37° |
| February | 37° | 20° | 1.8" | 7.7" | 7 | 9 | 15° – 39° |
| March | 49° | 29° | 2.5" | 3.5" | 8 | 3 | 31° – 55° |
| April | 63° | 39° | 3.7" | 0.6" | 9 | 0 | 42° – 57° |
| May | 73° | 50° | 4.5" | 0 | 11 | 0 | 56° – 69° |
| June | 82° | 60° | 4.6" | 0 | 9 | 0 | 67° – 75° |
| July | 84° | 63° | 4.4" | 0 | 7 | 0 | 69° – 80° |
| August | 83° | 61° | 3.7" | 0 | 7 | 0 | 67° – 78° |
| September | 78° | 54° | 3.4" | 0 | 6 | 0 | 60° – 70° |
| October | 65° | 42° | 3.2" | 0 | 8 | 0 | 50° – 59° |
| November | 50° | 32° | 2.7" | 1.1" | 7 | 1 | 33° – 49° |
| December | 38° | 22° | 2.1" | 6.3" | 7 | 7 | 15° – 40° |
| Year | 61° | 41° | 38.6" | 27.6" | 91 | 31 |
“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 Sullivan
Sullivan gets 39 inches of rain and melted snow a year. June is the wettest month and February the driest. Rain or snow falls on about 91 days a year. Snow covers the ground about 31 days of the year.
About 191 frost-free days a year
In half of years the last 32° night comes by April 16 and the first one by October 24. That leaves about 191 frost-free days for gardens, longer than 65% of U.S. towns.
Heating and cooling a home in Sullivan
Engineers use “degree days” to estimate how hard a furnace or air conditioner works. In Sullivan, 85% of that work is heating and 15% 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.
Sullivan and its neighbors
Sullivan borders 4 towns with climate data. January nights across them vary by 0.4°. Saunemin has the coldest January nights (16°) and Charlotte the hottest July afternoons (85°). Sullivan’s January low is 17° and its July high 84°.
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value.
How Sullivan 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 Sullivan averaged 1.3° warmer than the 1900s. The biggest change is in December (+2.6°). The shift is larger than in 58% of U.S. towns.
Change by month1991–2020 average minus 1901–2000 average, at Sullivan’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 15° to 40°. June is the most reliable, staying within 8°.
Common questions about Sullivan’s climate
What is the coldest month in Sullivan?
January, with a typical high of 32° and a low of 17°.
What is the hottest month in Sullivan?
July, with a typical high of 84° and a low of 63°. About 17 days a year reach 90°.
How much snow does Sullivan get?
About 28 inches in a normal winter, most of it in January.
When is the first frost in Sullivan?
In half of years the first 32° night comes by October 24, and the last spring frost by April 16.
What is the rainiest month in Sullivan?
June, with 4.6 inches of rain and melted snow. The year totals 39 inches.
Temperatures and rainfall come from NOAA’s gridded climate normals for Sullivan itself (about a 3-mile square). Snow, frost dates and day counts come from NOAA’s weather station at Chatsworth, IL (9 mi, snow) and Pontiac, IL (18 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.