Illinois Weather Trivia for October 22nd
- Frost occurs when the surface temperature cools to the dewpoint temperature, and both are at or below 32 degrees. Water vapor in the air turns directly into ice without becoming a liquid first, producing visible ice crystals on surfaces. Freezes occur when the air temperature (measured about 6 feet off the ground) falls below 32 degrees; temperatures of 28 degrees or colder are considered to be a hard freeze.
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