Allerton weather by month
What a typical year looks like in Allerton, Illinois: average highs and lows, rain and snow, and the warmest and coldest days on record. Normals are the 1991–2020 averages at Sidell 4n, 11 km from Allerton; records cover 2000–2026.
The year at a glance
- Precipitation a year
- 40.4 in1026 mm
- Snow a year
- 24 in60 cm
- Last spring freeze
- Apr 16
- First fall freeze
- Oct 12
- Heating degree days
- 5,855
- Cooling degree days
- 976
Freeze dates are medians (half of years earlier, half later). Degree days use a 65°F base; HVAC design temperatures here are −4°−20° (heating, 99%) and 94°34° (cooling, 1%).
Month by month
Allerton in January
Highs average 33°0° and lows 17°−8°, with 2.4 in60 mm of precipitation and 7 in18 cm of snow in a typical January.
- Record high
- 66°19° (2026)
- Record low
- −17°−27° (2009)
- Heating degree days
- 1243
- Cooling degree days
- 0
Allerton in February
Highs average 37°3° and lows 20°−6°, with 2 in51 mm of precipitation and 7 in17 cm of snow in a typical February.
- Record high
- 90°32° (2001)
- Record low
- −16°−27° (2015)
- Heating degree days
- 1015
- Cooling degree days
- 0
Allerton in March
Highs average 49°10° and lows 30°−1°, with 2.8 in70 mm of precipitation and 2.4 in6.1 cm of snow in a typical March.
- Record high
- 86°30° (2026)
- Record low
- −9°−23° (2015)
- Heating degree days
- 788
- Cooling degree days
- 2
Allerton in April
Highs average 62°17° and lows 41°5°, with 4.2 in105 mm of precipitation and 0.4 in1 cm of snow in a typical April.
- Record high
- 88°31° (2012)
- Record low
- 17°−8° (2021)
- Heating degree days
- 415
- Cooling degree days
- 9
Allerton in May
Highs average 73°23° and lows 53°12°, with 4.7 in118 mm of precipitation in a typical May.
- Record high
- 96°36° (2012)
- Record low
- 30°−1° (2005)
- Heating degree days
- 147
- Cooling degree days
- 86
Allerton in June
Highs average 82°28° and lows 62°17°, with 4.6 in117 mm of precipitation in a typical June.
- Record high
- 99°37° (2012)
- Record low
- 39°4° (2003)
- Heating degree days
- 14
- Cooling degree days
- 227
Allerton in July
Highs average 84°29° and lows 64°18°, with 4.7 in120 mm of precipitation in a typical July.
- Record high
- 102°39° (2012)
- Record low
- 48°9° (2024)
- Heating degree days
- 3
- Cooling degree days
- 286
Allerton in August
Highs average 83°28° and lows 62°16°, with 3.3 in83 mm of precipitation in a typical August.
- Record high
- 98°37° (2012)
- Record low
- 44°7° (2009)
- Heating degree days
- 8
- Cooling degree days
- 236
Allerton in September
Highs average 78°26° and lows 54°12°, with 2.7 in69 mm of precipitation in a typical September.
- Record high
- 99°37° (2011)
- Record low
- 34°1° (2003)
- Heating degree days
- 77
- Cooling degree days
- 109
Allerton in OctoberThis month
Highs average 65°19° and lows 43°6°, with 3.3 in85 mm of precipitation in a typical October.
- Record high
- 91°33° (2007)
- Record low
- 22°−6° (2010)
- Heating degree days
- 358
- Cooling degree days
- 20
Allerton in November
Highs average 50°10° and lows 32°0°, with 3.3 in85 mm of precipitation and 1.1 in2.8 cm of snow in a typical November.
- Record high
- 80°27° (2023)
- Record low
- 0°−18° (2019)
- Heating degree days
- 718
- Cooling degree days
- 1
Allerton in December
Highs average 38°3° and lows 23°−5°, with 2.5 in63 mm of precipitation and 6 in15 cm of snow in a typical December.
- Record high
- 71°22° (2012)
- Record low
- −10°−23° (2017)
- Heating degree days
- 1069
- Cooling degree days
- 0