Frost is water vapor, or water in gas form, that becomes solid. Frost usually forms on objects like cars, windows, and plants that are outside in air that is saturated, or filled, with moisture. Areas that have a lot of fog often have heavy frosts.

Frost forms when an outside surface cools past the dew point. The dew point is the point where the air gets so cold, the water vapor in the atmosphere turns into liquid. This liquid freezes. If it gets cold enough, little bits of ice, or frost, form. The ice is arranged in the form of ice crystals.

Frost is most common in low-lying areas. Warm air rises, and cool air sinks—cool air is denser than warm air. That means there are usually more water molecules in cool air than in warm air. As cool air collects in valleys, frost forms.

Frost usually forms at night, when the air temperature is cooler. Once the sun rises and warms the air around the frosted object, frost melts quickly.

Types of Frost

There are different types of frost. The most common are radiation frost (also called hoarfrost), advection frost, window frost, and rime.

Radiation frost is frost in the form of tiny ice crystals that usually shows up on the ground or exposed objects outside. Hoarfrost also forms in refrigerators and freezers.

Advection frost is a collection of small ice spikes. Advection frost forms when a cold wind blows over the branches of trees, poles, and other surfaces.

Window frost forms when a glass window is exposed to cold air outside and moist air inside. Window frost is familiar to winter residents of cold climates. Indoor heat and cold outdoor temperatures form this type of frost. Window frost was much more common before people began using double-paned windows.

Rime is frost that forms quickly, usually in very cold, wet climates. Rime also forms in windy weather. Rime sometimes looks like solid ice. Ships traveling through cold places like the Arctic Ocean often end up with rime covering at least part of the exposed part of the ship.

Frost and People

Frost can severely damage crops. It can destroy plants or fruits. Plants with thin skins, such as tomatoes, soy, or zucchini, can be ruined. If frost is bad enough, potatoes will freeze in the ground. Farmers have had entire fields destroyed in just a few frosty nights.

Farmers typically consult almanacs and maps to predict frost. Maps and information from almanacs (such as previous days of frost) tell farmers what areas usually receive frost, how often it occurs, and how long it lasts. These tools are reliable but are not always accurate.

Although farmers still rely on the weather, many spray their crops to reduce frost damage. This spray usually contains a genetically modified organism (GMO), an organism whose genes have been altered by people. The GMO that reduces frost damage to crops is called ice-minus bacteria. Ice-minus bacteria make it difficult for ice crystals to form. Ice-minus bacteria do no damage to the plant.

Many farmers also protect their crops by using the selective inverted sink (SIS) method. The selective inverted sink is a large fan that draws cold, moist air up into a chimney. The chimney expels the cold air far above the crops. This protects crops from frost without spraying them.

Sturdier plants are not destroyed by frost, but frost will stop them from growing. Evergreen trees, such as pine and spruce, will stop growing during a frost, but they won't die.

Roads can also be damaged by frost. Frosty roads are slippery and, exposed to the heat from cars, quickly become wet. Many drivers have trouble navigating frosty or wet roads.

frost
Hardy plants can withstand frost.

Father Frost
The Russian Santa Claus is named Ded Moroz, or Father Frost.

Rime of the Ancient Mariner
The English poet Samuel Taylor Coleridge wrote a famous poem called The Rime of the Ancient Mariner, published in 1798. In the poem, an old sailor tells the story of how his ship lost its way in a storm, eventually ending up in the Antarctic. Coleridges title is a play on words. Much of the story takes place in the Antarctic, on a ship that is covered with rime. The mariners long, white beard is compared to hoarfrost. Finally, The Rime of the Ancient Mariner is written in rhyme.

Don't Give These to Your Girlfriend
Frost flowers are formed when water in plant stems or trees oozes and freezes, sometimes in the shape of a flower. These types of "flowers" are rare, and when they do form, they're destroyed easily because they're so delicate.

accurate
Adjective

exact.

advection frost
Noun

ice crystals shaped like spikes that form from a cold wind.

Noun

layer of gases surrounding Earth.

almanac
Noun

annual publication containing a calendar, astronomical information, and weather forecasts.

Antarctic
Noun

region at Earth's extreme south, encompassed by the Antarctic Circle.

Arctic Ocean
Noun

one of Earth's four oceans, bordered by Asia, Europe, and North America.

Noun

all weather conditions for a given location over a period of time.

Noun

agricultural produce.

delicate
Adjective

fragile or easily damaged.

dense
Adjective

having parts or molecules that are packed closely together.

dew point
Noun

temperature at which water in the air condenses to form water droplets on objects near the ground.

evergreen
Noun

tree that does not lose its leaves.

expel
Verb

to eject or force out.

farmer
Noun

person who cultivates land and raises crops.

Noun

clouds at ground level.

freeze
Noun

weather pattern of temperatures below 0 degrees Celsius (32 degrees Fahrenheit).

Noun

thin coat of ice covering objects when the dew point is below freezing.

frost flower
Noun

ice crystals that form from moisture released by a plant stem or tree.

fruit
Noun

edible part of a plant that grows from a flower.

gas
Noun

state of matter with no fixed shape that will fill any container uniformly. Gas molecules are in constant, random motion.

gene
Noun

part of DNA that is the basic unit of heredity.

genetically modified organism (GMO)
Noun

living thing whose genes (DNA) have been altered for a specific purpose.

glass
Noun

brittle, transparent substance made from melted and fused minerals such as silica.

hoarfrost
Noun

ice crystals that form as water vapor near objects becomes solid. Also called radiation frost.

Noun

water in its solid form.

ice crystal
Noun

solid ice arranged in precise molecular form.

ice-minus bacteria
Noun

organism that makes it difficult for frost to form.

Noun

symbolic representation of selected characteristics of a place, usually drawn on a flat surface.

moisture
Noun

wetness.

molecule
Noun

smallest physical unit of a substance, consisting of two or more atoms linked together.

mountain
Noun

landmass that forms as tectonic plates interact with each other.

pane
Noun

sheet of glass or other material placed in a frame for a window.

pine
Noun

type of evergreen tree with needle-shaped leaves.

potato
Noun

plant native to the Americas.

predict
Verb

to know the outcome of a situation in advance.

radiation frost
Noun

ice crystals that form as water vapor near objects becomes solid. Also called hoarfrost.

refrigerator
Noun

space with artificially lowered temperature.

reliable
Adjective

dependable or consistent.

rhyme
Noun

word that has the same ending sound as another word.

rime
Noun

ice crystals that form in wet, windy conditions.

sailor
Noun

person who works aboard a ship.

Samuel Taylor Coleridge
Noun

(1772-1834) English poet.

saturate
Verb

to fill one substance with as much of another substance as it can take.

selective inverted sink (SIS)
Noun

method of preventing or reducing frost damage to crops by fanning cold, moist air up a chimney.

soy
Noun

beans, or fruit, of the soybean plant, native to Asia.

spruce
Noun

coniferous, or cone-bearing, tree.

Noun

degree of hotness or coldness measured by a thermometer with a numerical scale.

tomato
Noun

plant and fruit native to the Americas. Also considered a vegetable.

vapor
Noun

visible liquid suspended in the air, such as fog.

Noun

state of the atmosphere, including temperature, atmospheric pressure, wind, humidity, precipitation, and cloudiness.

wind
Noun

movement of air (from a high pressure zone to a low pressure zone) caused by the uneven heating of the Earth by the sun.

window frost
Noun

ice crystals that form when a window is exposed to freezing temperatures on one side and moist air on the other.

zucchini
Noun

type of vegetable (squash). Also called a courgette.