DeKalb weather by month
What a typical year looks like in DeKalb, Illinois: average highs and lows, rain and snow, and the warmest and coldest days on record. Normals are the 1991–2020 averages at DE KALB, 2 km from DeKalb; records cover 1966–2026.
The year at a glance
- Precipitation a year
- 37.3 in946 mm
- Snow a year
- 33 in84 cm
- Last spring freeze
- Apr 21
- First fall freeze
- Oct 15
- Heating degree days
- 6,744
- Cooling degree days
- 790
Freeze dates are medians (half of years earlier, half later). Degree days use a 65°F base; HVAC design temperatures here are −8°−22° (heating, 99%) and 93°34° (cooling, 1%).
Month by month
DeKalb in January
Highs average 28°−2° and lows 13°−10°, with 1.7 in43 mm of precipitation and 10 in26 cm of snow in a typical January.
- Record high
- 63°17° (1967)
- Record low
- −27°−33° (1985)
- Heating degree days
- 1376
- Cooling degree days
- 0
DeKalb in February
Highs average 33°0° and lows 17°−9°, with 1.7 in43 mm of precipitation and 9 in22 cm of snow in a typical February.
- Record high
- 75°24° (2024)
- Record low
- −26°−32° (2019)
- Heating degree days
- 1132
- Cooling degree days
- 0
DeKalb in March
Highs average 45°7° and lows 27°−3°, with 2.2 in57 mm of precipitation and 4 in11 cm of snow in a typical March.
- Record high
- 84°29° (1986)
- Record low
- −13°−25° (2002)
- Heating degree days
- 903
- Cooling degree days
- 1
DeKalb in April
Highs average 59°15° and lows 37°3°, with 3.6 in90 mm of precipitation and 1.3 in3.3 cm of snow in a typical April.
- Record high
- 92°33° (1986)
- Record low
- 8°−13° (1982)
- Heating degree days
- 515
- Cooling degree days
- 4
DeKalb in May
Highs average 70°21° and lows 49°10°, with 4.8 in122 mm of precipitation in a typical May.
- Record high
- 96°36° (2012)
- Record low
- 24°−4° (1989)
- Heating degree days
- 215
- Cooling degree days
- 51
DeKalb in June
Highs average 80°27° and lows 60°15°, with 4.6 in116 mm of precipitation in a typical June.
- Record high
- 101°38° (1988)
- Record low
- 34°1° (1993)
- Heating degree days
- 34
- Cooling degree days
- 175
DeKalb in July
Highs average 83°28° and lows 63°17°, with 4 in102 mm of precipitation in a typical July.
- Record high
- 102°39° (1995)
- Record low
- 43°6° (1967)
- Heating degree days
- 5
- Cooling degree days
- 259
DeKalb in August
Highs average 81°27° and lows 61°16°, with 4.1 in103 mm of precipitation in a typical August.
- Record high
- 103°39° (1988)
- Record low
- 39°4° (1986)
- Heating degree days
- 12
- Cooling degree days
- 206
DeKalb in September
Highs average 75°24° and lows 53°12°, with 3.3 in84 mm of precipitation in a typical September.
- Record high
- 95°35° (2026)
- Record low
- 27°−3° (1991)
- Heating degree days
- 114
- Cooling degree days
- 85
DeKalb in OctoberThis month
Highs average 62°17° and lows 41°5°, with 3 in75 mm of precipitation and 0.1 in0.3 cm of snow in a typical October.
- Record high
- 89°32° (1976)
- Record low
- 13°−11° (1988)
- Heating degree days
- 428
- Cooling degree days
- 9
DeKalb in November
Highs average 46°8° and lows 30°−1°, with 2.3 in59 mm of precipitation and 1.8 in4.6 cm of snow in a typical November.
- Record high
- 76°24° (1999)
- Record low
- −8°−22° (1976)
- Heating degree days
- 812
- Cooling degree days
- 0
DeKalb in December
Highs average 34°1° and lows 19°−7°, with 2 in52 mm of precipitation and 7 in17 cm of snow in a typical December.
- Record high
- 69°21° (2012)
- Record low
- −22°−30° (1983)
- Heating degree days
- 1198
- Cooling degree days
- 0