Rio weather by month
What a typical year looks like in Rio, Illinois: average highs and lows, rain and snow, and the warmest and coldest days on record. Normals are the 1991–2020 averages at GALESBURG, 18 km from Rio; records cover 1896–2026.
The year at a glance
- Precipitation a year
- 39 in990 mm
- Snow a year
- 26 in66 cm
- Last spring freeze
- Apr 17
- First fall freeze
- Oct 16
- Heating degree days
- 6,323
- Cooling degree days
- 971
Freeze dates are medians (half of years earlier, half later). Degree days use a 65°F base; HVAC design temperatures here are −6°−21° (heating, 99%) and 93°34° (cooling, 1%).
Month by month
Rio in January
Highs average 30°−1° and lows 14°−10°, with 1.7 in43 mm of precipitation and 9 in23 cm of snow in a typical January.
- Record high
- 68°20° (1909)
- Record low
- −27°−33° (2009)
- Heating degree days
- 1336
- Cooling degree days
- 0
Rio in February
Highs average 35°2° and lows 17°−8°, with 1.9 in47 mm of precipitation and 7 in17 cm of snow in a typical February.
- Record high
- 74°23° (2024)
- Record low
- −28°−33° (1905)
- Heating degree days
- 1092
- Cooling degree days
- 0
Rio in March
Highs average 48°9° and lows 28°−2°, with 2.4 in61 mm of precipitation and 2.3 in5.8 cm of snow in a typical March.
- Record high
- 86°30° (1986)
- Record low
- −14°−26° (1960)
- Heating degree days
- 837
- Cooling degree days
- 1
Rio in April
Highs average 61°16° and lows 40°4°, with 3.8 in97 mm of precipitation and 0.4 in1 cm of snow in a typical April.
- Record high
- 91°33° (1952)
- Record low
- 9°−13° (1899)
- Heating degree days
- 441
- Cooling degree days
- 9
Rio in May
Highs average 72°22° and lows 52°11°, with 5.3 in134 mm of precipitation in a typical May.
- Record high
- 96°36° (2018)
- Record low
- 24°−4° (1903)
- Heating degree days
- 168
- Cooling degree days
- 70
Rio in June
Highs average 81°27° and lows 62°17°, with 4.6 in116 mm of precipitation in a typical June.
- Record high
- 102°39° (1936)
- Record low
- 36°2° (1903)
- Heating degree days
- 19
- Cooling degree days
- 217
Rio in July
Highs average 84°29° and lows 65°19°, with 4 in103 mm of precipitation in a typical July.
- Record high
- 112°44° (1936)
- Record low
- 42°6° (1899)
- Heating degree days
- 2
- Cooling degree days
- 303
Rio in August
Highs average 82°28° and lows 63°17°, with 3.9 in99 mm of precipitation in a typical August.
- Record high
- 102°39° (1936)
- Record low
- 41°5° (1908)
- Heating degree days
- 6
- Cooling degree days
- 250
Rio in September
Highs average 76°25° and lows 55°13°, with 3.9 in98 mm of precipitation in a typical September.
- Record high
- 100°38° (1899)
- Record low
- 19°−7° (1899)
- Heating degree days
- 93
- Cooling degree days
- 107
Rio in OctoberThis month
Highs average 63°17° and lows 43°6°, with 2.8 in72 mm of precipitation in a typical October.
- Record high
- 94°34° (2006)
- Record low
- 17°−8° (2001)
- Heating degree days
- 394
- Cooling degree days
- 14
Rio in November
Highs average 48°9° and lows 30°−1°, with 2.6 in66 mm of precipitation and 1.7 in4.3 cm of snow in a typical November.
- Record high
- 79°26° (1950)
- Record low
- −6°−21° (1898)
- Heating degree days
- 782
- Cooling degree days
- 0
Rio in December
Highs average 35°2° and lows 20°−7°, with 2.1 in54 mm of precipitation and 6 in15 cm of snow in a typical December.
- Record high
- 72°22° (2021)
- Record low
- −22°−30° (1963)
- Heating degree days
- 1153
- Cooling degree days
- 0