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Know Your Frost Types?

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Know Your Frost Types?

It’s late fall and temperatures are dropping, which means frost is descending on much of the U.S. and Canada. Driveways are slippery, windshields need to be scraped, trees and grass will appear ghostly grey, and any garden plants that haven’t been harvested may be lost. There are many different types of frost—here’s a list of the types you might see on these chilly mornings and what they look like.

What Causes Frost?

Frost forms when the temperatures on surfaces, such as cars and trees, drop below freezing, causing water vapor to form into ice crystals. This happens most often on clear, cold nights, when there are no clouds to hold warmth in.

The earliest frost date listed in the Farmers’ Almanac is for Green River Wyoming, which usually sees its first frost of the year around September 4th. Mid- to late-October is the most common time of the year for first frost dates across the United States. Florida has the latest frost dates of any state, with many areas seeing only a couple of days of frost per year, during the month of January.

See our frost dates with an interactive map here.

There are actually several different kinds of frost. Here’s a look at some common varieties:

Rime Frost

Rime frost looks like sugar sprinkled onto the edges of leaves and flower petals. It occurs whenever damp winds are coupled with extremely low temperatures. The word “rime” means “crust.”

Rime frost

Hoar Frost

Hoar frost is frost that resembles spiky hairs. This type of frost gets its name from the word “hoar,” which means “ancient,” because it resembles an old man’s bushy, white beard. It happens when water vapor freezes instantly after coming into contact with a very cold surface.

Hoar frost

Fern Frost

Fern frost is a kind of frost that appears on windows when there is very cold air on one side and moist air on the other. This causes tiny water droplets to form on the cold glass and freeze into patterns that resemble leaves or ferns.

Fern frost

Be sure to check out the Farmers’ Almanac’s list of average frost dates to keep track of frost to hit your area. And don’t miss these must-read tips on how to protect your garden from frost.

4 comments

1 Jaime McLeod { 08.02.13 at 3:45 pm }

ct0065 – Your average first frost is October 4. We predict light snow by the end of October.

2 ct0065 { 08.01.13 at 5:26 pm }

When will colorado get first frost and first snow in denver metro area

3 Margaret Elaine Adams { 12.19.11 at 8:01 am }

It has been not to cold in Knox Indiana,
with lite on the snow.

4 Retired Drill Sergeant { 10.13.10 at 11:08 am }

First significant frost in Southeastern CT (New London County) was Sunday 10/10 32 degrees frost on grass, autos, etc.

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