What makes a ‘hard freeze’ different?
Extended periods below 28 degrees qualify for the term
Just as you might think, a “hard freeze” can have much bigger consequences than a lighter one. What you may not know is that there’s actually a technical definition set forth by the National Weather Service.
Generally, a “freeze” happens anytime temperatures drop to 32 degrees or lower. But to be considered a “hard” freeze, temperatures must drop to at least 28 degrees and stay there for a significant amount of time, usually at least a few hours.
Whenever hard freezes occur, the cold temperatures are more likely to kill outdoor plants and crops. Also, it’s more likely that outdoor, exposed pipes could be damaged during a hard freeze.
For indoor pipes to freeze, it normally takes even colder temperatures. According to Texas A&M University, temperatures down to 20 degrees or lower put indoor pipes at risk.
During instances of frigid weather, the weather service may issue a “freeze warning.” These alerts go out when ground-level temperatures are expected to drop below freezing over a large area for an extended period, regardless of whether frost develops.
So what qualifies as frost? The weather service defines frost as “the formation of thin ice crystals on the ground or other surfaces in the form of scales, needles, feathers, or fans.”
Like dew, frost develops when cooler surface temperatures cause water vapor in the air to condense into liquid beads, except the temperatures of the Earth’s surface and earthbound objects fall below 32 degrees.
“If a frost period is sufficiently severe to end the growing season or delay its beginning, it is commonly referred to as a ‘killing frost,’” the weather service explains in its online glossary.