Sullivan weather by month
What a typical year looks like in Sullivan, Illinois: average highs and lows, rain and snow, and the warmest and coldest days on record. Normals are the 1991–2020 averages at Windsor, 17 km from Sullivan; records cover 1904–2026.
The year at a glance
- Precipitation a year
- 41.2 in1046 mm
- Snow a year
- 14 in35 cm
- Last spring freeze
- Apr 12
- First fall freeze
- Oct 18
- Heating degree days
- 5,491
- Cooling degree days
- 1,024
Freeze dates are medians (half of years earlier, half later). Degree days use a 65°F base; HVAC design temperatures here are 0°−18° (heating, 99%) and 95°35° (cooling, 1%).
Month by month
Sullivan in January
Highs average 35°1° and lows 19°−7°, with 2.6 in67 mm of precipitation and 5 in13 cm of snow in a typical January.
- Record high
- 74°23° (1909)
- Record low
- −26°−32° (1915)
- Heating degree days
- 1181
- Cooling degree days
- 0
Sullivan in February
Highs average 40°4° and lows 23°−5°, with 2 in50 mm of precipitation and 3 in9 cm of snow in a typical February.
- Record high
- 75°24° (1972)
- Record low
- −24°−31° (1910)
- Heating degree days
- 946
- Cooling degree days
- 0
Sullivan in March
Highs average 51°11° and lows 32°0°, with 3.1 in79 mm of precipitation and 1.4 in3.6 cm of snow in a typical March.
- Record high
- 89°32° (1910)
- Record low
- −7°−22° (1960)
- Heating degree days
- 733
- Cooling degree days
- 2
Sullivan in April
Highs average 64°18° and lows 42°5°, with 4.5 in115 mm of precipitation and 0.3 in0.8 cm of snow in a typical April.
- Record high
- 90°32° (1930)
- Record low
- 19°−7° (1920)
- Heating degree days
- 374
- Cooling degree days
- 11
Sullivan in May
Highs average 74°23° and lows 53°12°, with 4.6 in116 mm of precipitation in a typical May.
- Record high
- 97°36° (1913)
- Record low
- 27°−3° (1925)
- Heating degree days
- 132
- Cooling degree days
- 82
Sullivan in June
Highs average 82°28° and lows 62°16°, with 4.8 in121 mm of precipitation in a typical June.
- Record high
- 105°41° (1954)
- Record low
- 35°2° (1917)
- Heating degree days
- 14
- Cooling degree days
- 220
Sullivan in July
Highs average 85°29° and lows 65°18°, with 3.9 in99 mm of precipitation in a typical July.
- Record high
- 111°44° (1936)
- Record low
- 43°6° (1904)
- Heating degree days
- 2
- Cooling degree days
- 307
Sullivan in August
Highs average 84°29° and lows 63°17°, with 3 in75 mm of precipitation in a typical August.
- Record high
- 107°42° (1918)
- Record low
- 37°3° (1915)
- Heating degree days
- 6
- Cooling degree days
- 257
Sullivan in September
Highs average 78°26° and lows 55°13°, with 3 in75 mm of precipitation in a typical September.
- Record high
- 106°41° (1954)
- Record low
- 26°−3° (1942)
- Heating degree days
- 69
- Cooling degree days
- 123
Sullivan in OctoberThis month
Highs average 66°19° and lows 44°7°, with 3.6 in91 mm of precipitation in a typical October.
- Record high
- 95°35° (1922)
- Record low
- 16°−9° (1925)
- Heating degree days
- 322
- Cooling degree days
- 21
Sullivan in November
Highs average 51°11° and lows 33°1°, with 3.8 in95 mm of precipitation and 0.8 in2 cm of snow in a typical November.
- Record high
- 84°29° (1965)
- Record low
- −6°−21° (1950)
- Heating degree days
- 688
- Cooling degree days
- 1
Sullivan in December
Highs average 39°4° and lows 25°−4°, with 2.5 in62 mm of precipitation and 2.6 in6.6 cm of snow in a typical December.
- Record high
- 72°22° (1948)
- Record low
- −20°−29° (1989)
- Heating degree days
- 1024
- Cooling degree days
- 0