Frost dates in Mason City, IL
The average last spring frost in Mason City is around April 18 and the first fall frost is around October 14. That gives Mason City an average growing season of about 179 days.
Last spring frost
| Early (10% chance after) | March 31 |
|---|---|
| Average (50%) | April 18 |
| Late (90%) | April 30 |
First fall frost
| Early (10%) | September 24 |
|---|---|
| Average (50%) | October 14 |
| Late (90% chance before) | November 1 |