Freeze Warning: Cover Your Plants, Air Temp Doesn't Tell Full Story

By Chris Spears

DENVER (CBS4) - Freeze warnings have been issued for early Wednesday morning across a large part of Colorado, including the entire Interstate 25 urban corridor, between Colorado Springs, Denver and Fort Collins.

A freeze warning means that widespread freezing temperatures are possible.

But don't sit and wait for the official temperature to reach 32°F before you decide to take action to protect tender plants.

That's because air temperatures are taken 5.5 feet off the ground. Most plants are only a few inches to a few feet off the ground where the temperatures are often actually much colder than the 'air' temperature.

Once the sun sets each day a process called radiational cooling takes place. In other words, the ground immediately begins to cool and it will cool all night long.

By sunrise the next morning, the coldest temperatures in the lower atmosphere can actually be recorded right at or near the ground.

If you took the time to place a series of thermometers between the ground and where we take official temperatures 5.5 feet up, you'd find a tremendous difference, potentially by several degrees.

So while the air temperature could read 33°F on an 'official' thermometer, it might actually be 28°F five inches above the ground where a tender plant lives.

In case you're wondering, the opposite happens during the day.

Intense solar heating will actually cause the warmest temperatures in the lower atmosphere to be found right at and slightly above the ground.

Meteorologist Chris Spears writes about stories related to weather and climate in Colorado. Check out his bio, connect with him on Facebook or follow him on Twitter @ChrisCBS4.