Marietta Illinois Climate Data

Monthly Average Climate Data for Marietta Illinois

Switch Data to Celsius/Metric Units
MonthAvg. LowAvg. HighAvg. Precip
January15.6 °F32.8 °F1.87 in.
February19.1 °F37.4 °F1.9 in.
March29.3 °F50.0 °F2.54 in.
April40.0 °F63.2 °F3.81 in.
May52.0 °F73.7 °F5.03 in.
June61.6 °F82.5 °F4.83 in.
July64.7 °F85.6 °F4.0 in.
August62.3 °F83.9 °F3.46 in.
September54.2 °F78.2 °F3.62 in.
October42.3 °F65.8 °F3.04 in.
November31.1 °F50.6 °F2.49 in.
December21.5 °F38.0 °F1.92 in.
Annual41.1 °F61.8 °F38.51 in.

Climate Data for Marietta Illinois

Average First Frost DateOct. 11 - Oct. 20
Average Last Frost DateApr. 21 - Apr. 30
Average Days With Frost100-125 Days
Plant Hardiness Zone - 2023Zone 6a : -10°F to -5°F
Plant Hardiness Zone - 2012Zone 5b : -15°F to -10°F
Current Drought ConditionsModerate Drought
Köppen Climate ClassificationDfa - Humid Continental Hot Summers With Year Around Precipitation
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