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What is a hard freeze warning?

Posted November 10, 2007
Updated November 3

What is the difference between a hard freeze, deep freeze or frost?

Mike Moss: Hard freeze does not have an "official" definition of the term. In general, "hard freeze" is used to imply temperatures that are sufficiently cold, for a long enough period, to seriously damage or kill seasonal vegetation. In our area, this usually means temperatures falling into the upper 20s or lower for at least two to three hours. There are some weather service offices that have established specific criteria for a hard freeze watch or warning that may be more intense than the generic definition I just listed - for example, the Mobile AL forecast office lists criteria for its hard freeze warning as temperatures 26 degrees or lower for at least 5 hours. They intend this warning to alert people to the potential for frozen pipes, radiators, livestock and so on, not just damage to sensitive plants.

A hard freeze is different than a frost in that a frost is not always below the typical freezing point of 32 degrees or low 30s.

More Information: frost, hard frost, frost alert, frost advisory, temperatures below freezing, a hard freeze watch, hydrologic outlook, what temperature is considered freezing, advisory frost, humidity and frost temperatures

Full question from Larry Roberson: What is the official definition of a hard freeze?

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