Shannon weather by month
What a typical year looks like in Shannon, Illinois: average highs and lows, rain and snow, and the warmest and coldest days on record. Normals are the 1991–2020 averages at Mount Carroll, 21 km from Shannon; records cover 1897–2026.
The year at a glance
- Precipitation a year
- 40.3 in1024 mm
- Snow a year
- 33 in85 cm
- Last spring freeze
- May 3
- First fall freeze
- Oct 2
- Heating degree days
- 6,733
- Cooling degree days
- 744
Freeze dates are medians (half of years earlier, half later). Degree days use a 65°F base; HVAC design temperatures here are −13°−25° (heating, 99%) and 94°34° (cooling, 1%).
Month by month
Shannon in January
Highs average 31°−1° and lows 11°−12°, with 1.7 in42 mm of precipitation and 10 in26 cm of snow in a typical January.
- Record high
- 61°16° (1944)
- Record low
- −38°−39° (2019)
- Heating degree days
- 1370
- Cooling degree days
- 0
Shannon in February
Highs average 35°2° and lows 14°−10°, with 1.8 in46 mm of precipitation and 8 in20 cm of snow in a typical February.
- Record high
- 75°24° (2024)
- Record low
- −36°−38° (2019)
- Heating degree days
- 1126
- Cooling degree days
- 0
Shannon in March
Highs average 48°9° and lows 26°−4°, with 2.5 in64 mm of precipitation and 4 in9 cm of snow in a typical March.
- Record high
- 85°29° (1986)
- Record low
- −16°−27° (1962)
- Heating degree days
- 882
- Cooling degree days
- 1
Shannon in April
Highs average 61°16° and lows 36°2°, with 3.9 in99 mm of precipitation and 0.8 in2 cm of snow in a typical April.
- Record high
- 92°33° (1930)
- Record low
- −2°−19° (1982)
- Heating degree days
- 509
- Cooling degree days
- 5
Shannon in May
Highs average 72°22° and lows 47°8°, with 4.6 in116 mm of precipitation in a typical May.
- Record high
- 104°40° (1934)
- Record low
- 15°−9° (1989)
- Heating degree days
- 211
- Cooling degree days
- 50
Shannon in June
Highs average 82°28° and lows 57°14°, with 5.5 in139 mm of precipitation in a typical June.
- Record high
- 104°40° (1934)
- Record low
- 31°−1° (1903)
- Heating degree days
- 35
- Cooling degree days
- 165
Shannon in July
Highs average 85°29° and lows 60°16°, with 4.9 in124 mm of precipitation in a typical July.
- Record high
- 108°42° (1936)
- Record low
- 35°2° (1904)
- Heating degree days
- 7
- Cooling degree days
- 244
Shannon in August
Highs average 83°29° and lows 58°15°, with 3.9 in99 mm of precipitation in a typical August.
- Record high
- 103°39° (1936)
- Record low
- 32°0° (1986)
- Heating degree days
- 16
- Cooling degree days
- 192
Shannon in September
Highs average 77°25° and lows 50°10°, with 3.7 in94 mm of precipitation in a typical September.
- Record high
- 99°37° (1922)
- Record low
- 14°−10° (1899)
- Heating degree days
- 130
- Cooling degree days
- 77
Shannon in OctoberThis month
Highs average 64°18° and lows 38°3°, with 3 in77 mm of precipitation and 0.4 in1 cm of snow in a typical October.
- Record high
- 91°33° (1997)
- Record low
- 4°−16° (1925)
- Heating degree days
- 440
- Cooling degree days
- 10
Shannon in November
Highs average 49°9° and lows 27°−3°, with 2.6 in66 mm of precipitation and 1.7 in4.3 cm of snow in a typical November.
- Record high
- 79°26° (1933)
- Record low
- −15°−26° (1976)
- Heating degree days
- 812
- Cooling degree days
- 0
Shannon in December
Highs average 36°2° and lows 17°−8°, with 2.2 in56 mm of precipitation and 9 in22 cm of snow in a typical December.
- Record high
- 71°22° (2021)
- Record low
- −28°−33° (1914)
- Heating degree days
- 1195
- Cooling degree days
- 0