Union weather by month
What a typical year looks like in Union, Illinois: average highs and lows, rain and snow, and the warmest and coldest days on record. Normals are the 1991–2020 averages at Crystal Lake 4nw, 13 km from Union; records cover 2000–2026.
The year at a glance
- Precipitation a year
- 39.3 in999 mm
- Snow a year
- 35 in89 cm
- Last spring freeze
- Apr 22
- First fall freeze
- Oct 29
- Heating degree days
- 6,519
- Cooling degree days
- 771
Freeze dates are medians (half of years earlier, half later). Degree days use a 65°F base; HVAC design temperatures here are −7°−21° (heating, 99%) and 95°35° (cooling, 1%).
Month by month
Union in January
Highs average 32°0° and lows 14°−10°, with 2 in50 mm of precipitation and 10 in25 cm of snow in a typical January.
- Record high
- 59°15° (2013)
- Record low
- −28°−33° (2019)
- Heating degree days
- 1306
- Cooling degree days
- 0
Union in February
Highs average 35°2° and lows 16°−9°, with 1.8 in47 mm of precipitation and 9 in23 cm of snow in a typical February.
- Record high
- 76°24° (2024)
- Record low
- −29°−34° (2019)
- Heating degree days
- 1099
- Cooling degree days
- 0
Union in March
Highs average 47°8° and lows 26°−3°, with 2.5 in64 mm of precipitation and 4 in11 cm of snow in a typical March.
- Record high
- 85°29° (2012)
- Record low
- −8°−22° (2015)
- Heating degree days
- 883
- Cooling degree days
- 2
Union in April
Highs average 59°15° and lows 37°3°, with 3.8 in96 mm of precipitation and 1.2 in3 cm of snow in a typical April.
- Record high
- 86°30° (2021)
- Record low
- 17°−8° (2018)
- Heating degree days
- 513
- Cooling degree days
- 2
Union in May
Highs average 71°22° and lows 48°9°, with 5 in126 mm of precipitation in a typical May.
- Record high
- 97°36° (2018)
- Record low
- 28°−2° (2020)
- Heating degree days
- 218
- Cooling degree days
- 51
Union in June
Highs average 80°27° and lows 58°15°, with 5.3 in134 mm of precipitation in a typical June.
- Record high
- 98°37° (2012)
- Record low
- 41°5° (2025)
- Heating degree days
- 31
- Cooling degree days
- 162
Union in July
Highs average 84°29° and lows 63°17°, with 3.9 in99 mm of precipitation in a typical July.
- Record high
- 103°39° (2012)
- Record low
- 49°9° (2015)
- Heating degree days
- 5
- Cooling degree days
- 261
Union in August
Highs average 82°28° and lows 61°16°, with 3.8 in97 mm of precipitation in a typical August.
- Record high
- 99°37° (2023)
- Record low
- 49°9° (2017)
- Heating degree days
- 11
- Cooling degree days
- 215
Union in September
Highs average 74°24° and lows 52°11°, with 3.5 in90 mm of precipitation in a typical September.
- Record high
- 95°35° (2013)
- Record low
- 38°3° (2012)
- Heating degree days
- 121
- Cooling degree days
- 73
Union in OctoberThis month
Highs average 62°17° and lows 42°6°, with 3.2 in81 mm of precipitation and 0.2 in0.5 cm of snow in a typical October.
- Record high
- 87°31° (2010)
- Record low
- 26°−3° (2018)
- Heating degree days
- 404
- Cooling degree days
- 5
Union in November
Highs average 48°9° and lows 31°−1°, with 2.5 in63 mm of precipitation and 1.6 in4.1 cm of snow in a typical November.
- Record high
- 74°23° (2020)
- Record low
- 4°−16° (2019)
- Heating degree days
- 780
- Cooling degree days
- 0
Union in December
Highs average 36°2° and lows 20°−6°, with 2.1 in53 mm of precipitation and 9 in22 cm of snow in a typical December.
- Record high
- 66°19° (2012)
- Record low
- −10°−23° (2016)
- Heating degree days
- 1148
- Cooling degree days
- 0