Ottawa weather by month
What a typical year looks like in Ottawa, Illinois: average highs and lows, rain and snow, and the warmest and coldest days on record. Normals are the 1991–2020 averages at Ottawa 4sw, 8 km from Ottawa; records cover 1890–2026.
The year at a glance
- Precipitation a year
- 36.2 in919 mm
- Snow a year
- 24 in60 cm
- Last spring freeze
- Apr 18
- First fall freeze
- Oct 17
- Heating degree days
- 6,210
- Cooling degree days
- 866
Freeze dates are medians (half of years earlier, half later). Degree days use a 65°F base; HVAC design temperatures here are −5°−21° (heating, 99%) and 94°34° (cooling, 1%).
Month by month
Ottawa in January
Highs average 31°−1° and lows 15°−9°, with 1.8 in45 mm of precipitation and 9 in23 cm of snow in a typical January.
- Record high
- 68°20° (1909)
- Record low
- −26°−32° (1893)
- Heating degree days
- 1303
- Cooling degree days
- 0
Ottawa in February
Highs average 35°2° and lows 19°−7°, with 1.5 in39 mm of precipitation and 5 in13 cm of snow in a typical February.
- Record high
- 73°23° (1921)
- Record low
- −23°−31° (1899)
- Heating degree days
- 1064
- Cooling degree days
- 0
Ottawa in March
Highs average 48°9° and lows 29°−2°, with 2.3 in58 mm of precipitation and 3 in8 cm of snow in a typical March.
- Record high
- 85°29° (1910)
- Record low
- −9°−23° (2014)
- Heating degree days
- 829
- Cooling degree days
- 2
Ottawa in April
Highs average 61°16° and lows 39°4°, with 3.5 in90 mm of precipitation and 0.4 in1 cm of snow in a typical April.
- Record high
- 93°34° (1930)
- Record low
- 12°−11° (1899)
- Heating degree days
- 449
- Cooling degree days
- 8
Ottawa in May
Highs average 72°22° and lows 51°11°, with 4.5 in114 mm of precipitation in a typical May.
- Record high
- 106°41° (1934)
- Record low
- 26°−3° (1923)
- Heating degree days
- 177
- Cooling degree days
- 63
Ottawa in June
Highs average 80°27° and lows 61°16°, with 4.4 in112 mm of precipitation in a typical June.
- Record high
- 107°42° (1934)
- Record low
- 35°2° (1929)
- Heating degree days
- 28
- Cooling degree days
- 184
Ottawa in July
Highs average 83°28° and lows 64°18°, with 3.6 in92 mm of precipitation in a typical July.
- Record high
- 112°44° (1901)
- Record low
- 39°4° (1920)
- Heating degree days
- 4
- Cooling degree days
- 272
Ottawa in August
Highs average 82°28° and lows 62°17°, with 3.7 in94 mm of precipitation in a typical August.
- Record high
- 107°42° (1918)
- Record low
- 33°1° (1915)
- Heating degree days
- 9
- Cooling degree days
- 224
Ottawa in September
Highs average 76°25° and lows 54°12°, with 3.2 in82 mm of precipitation in a typical September.
- Record high
- 103°39° (1899)
- Record low
- 25°−4° (1928)
- Heating degree days
- 90
- Cooling degree days
- 99
Ottawa in OctoberThis month
Highs average 64°18° and lows 43°6°, with 3.1 in79 mm of precipitation in a typical October.
- Record high
- 94°34° (1963)
- Record low
- 13°−11° (1895)
- Heating degree days
- 376
- Cooling degree days
- 14
Ottawa in November
Highs average 49°9° and lows 32°0°, with 2.5 in64 mm of precipitation and 0.8 in2 cm of snow in a typical November.
- Record high
- 83°28° (1950)
- Record low
- −6°−21° (1930)
- Heating degree days
- 750
- Cooling degree days
- 0
Ottawa in December
Highs average 36°2° and lows 21°−6°, with 2 in51 mm of precipitation and 5 in12 cm of snow in a typical December.
- Record high
- 71°22° (2012)
- Record low
- −23°−31° (1924)
- Heating degree days
- 1131
- Cooling degree days
- 0