Port Byron weather by month
What a typical year looks like in Port Byron, Illinois: average highs and lows, rain and snow, and the warmest and coldest days on record. Normals are the 1991–2020 averages at CLINTON NO 1, 20 km from Port Byron; records cover 1893–2026.
The year at a glance
- Precipitation a year
- 36.4 in926 mm
- Snow a year
- 32 in81 cm
- Last spring freeze
- Apr 19
- First fall freeze
- Oct 13
- Heating degree days
- 6,266
- Cooling degree days
- 919
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
Port Byron in January
Highs average 29°−1° and lows 14°−10°, with 1.5 in37 mm of precipitation and 9 in23 cm of snow in a typical January.
- Record high
- 69°21° (1944)
- Record low
- −29°−34° (2019)
- Heating degree days
- 1337
- Cooling degree days
- 0
Port Byron in February
Highs average 34°1° and lows 18°−8°, with 1.7 in43 mm of precipitation and 8 in19 cm of snow in a typical February.
- Record high
- 77°25° (2024)
- Record low
- −29°−34° (1996)
- Heating degree days
- 1082
- Cooling degree days
- 0
Port Byron in March
Highs average 48°9° and lows 29°−2°, with 2.3 in59 mm of precipitation and 4 in10 cm of snow in a typical March.
- Record high
- 87°31° (1986)
- Record low
- −15°−26° (2014)
- Heating degree days
- 819
- Cooling degree days
- 2
Port Byron in April
Highs average 62°17° and lows 40°4°, with 3.4 in86 mm of precipitation and 0.8 in2 cm of snow in a typical April.
- Record high
- 94°34° (1930)
- Record low
- 7°−14° (1982)
- Heating degree days
- 428
- Cooling degree days
- 9
Port Byron in May
Highs average 73°23° and lows 51°11°, with 4.4 in112 mm of precipitation in a typical May.
- Record high
- 102°39° (1934)
- Record low
- 24°−4° (2005)
- Heating degree days
- 159
- Cooling degree days
- 68
Port Byron in June
Highs average 81°27° and lows 61°16°, with 4.7 in120 mm of precipitation in a typical June.
- Record high
- 107°42° (1910)
- Record low
- 37°3° (1903)
- Heating degree days
- 19
- Cooling degree days
- 202
Port Byron in July
Highs average 84°29° and lows 65°18°, with 3.9 in99 mm of precipitation in a typical July.
- Record high
- 109°43° (1936)
- Record low
- 41°5° (1902)
- Heating degree days
- 2
- Cooling degree days
- 292
Port Byron in August
Highs average 82°28° and lows 63°17°, with 4.2 in107 mm of precipitation in a typical August.
- Record high
- 106°41° (1936)
- Record low
- 39°4° (1934)
- Heating degree days
- 8
- Cooling degree days
- 231
Port Byron in September
Highs average 76°24° and lows 55°13°, with 3.7 in94 mm of precipitation in a typical September.
- Record high
- 103°39° (1913)
- Record low
- 19°−7° (1899)
- Heating degree days
- 94
- Cooling degree days
- 101
Port Byron in OctoberThis month
Highs average 63°17° and lows 43°6°, with 2.6 in67 mm of precipitation and 0.3 in0.8 cm of snow in a typical October.
- Record high
- 92°33° (1953)
- Record low
- 7°−14° (1925)
- Heating degree days
- 384
- Cooling degree days
- 14
Port Byron in November
Highs average 48°9° and lows 31°−1°, with 2.2 in56 mm of precipitation and 2.3 in5.8 cm of snow in a typical November.
- Record high
- 80°27° (1933)
- Record low
- −8°−22° (1976)
- Heating degree days
- 773
- Cooling degree days
- 0
Port Byron in December
Highs average 35°1° and lows 21°−6°, with 1.9 in47 mm of precipitation and 8 in20 cm of snow in a typical December.
- Record high
- 74°23° (2021)
- Record low
- −27°−33° (1963)
- Heating degree days
- 1161
- Cooling degree days
- 0