Weather and Climate

Clouds are made of tiny water droplets or ice crystals floating high above the ground.

Fog is simply a cloud that has formed at ground level instead of high up.

Cumulus clouds look like piled cotton and often signal calm, pleasant weather.

Stratus clouds form flat gray layers that can cover the whole sky for days.

Cirrus clouds are thin and wispy, made of ice crystals far above the surface.

Rain begins when droplets inside a cloud grow heavy enough to fall downward.

Snow forms when water vapor turns directly into ice crystals without becoming liquid first.

Hail stones grow inside storm clouds as ice layers build up around a frozen core.

Sleet is rain that freezes into small pellets before reaching the ground below.

Freezing rain turns to ice the moment it touches a cold road or branch.

Dew appears overnight when cool surfaces pull moisture out of the surrounding air.

Frost forms when water vapor freezes straight onto a cold surface as tiny crystals.

Humidity describes how much water vapor the air is holding at a given moment.

Wind happens because air moves from areas of high pressure toward lower pressure.

Sea breezes blow inland during the day because land heats faster than the ocean.

Trade winds blow steadily across tropical oceans and have guided sailors for many centuries.

A breeze feels cooler than still air because moving air carries heat away from skin.

Wind is measured with an anemometer, a device with cups that spin in moving air.

Rainfall is measured by collecting water in a gauge and reading the depth in millimeters.

Barometers track air pressure, and a rapid fall often means a storm is coming.

Thermometers measure temperature, usually by how far a liquid expands inside a narrow tube.

Lightning is a huge electric spark that jumps between clouds or toward the ground.

Thunder is the sound of air expanding rapidly after lightning heats it to extreme temperatures.

The gap between a flash and its thunder gives a rough sense of distance.

Rainbows appear when sunlight bends inside raindrops and splits into separate colors.

A rainbow appears in the part of the sky directly opposite the sun.

Halos around the sun or moon come from light passing through tiny ice crystals.

Red sunsets happen because sunlight travels through more air and loses its blue wavelengths.

Seasons happen because Earth's axis is tilted, not because of distance from the sun.

Summer days feel hotter because sunlight strikes the ground at a steeper angle.

The equator stays warm all year because it receives the most direct sunlight.

Mountains are colder than valleys because thin air at altitude holds less heat.

Coastal places have milder temperature swings than inland areas at the same latitude.

Snow reflects most sunlight, which is why bright snowfields feel surprisingly harsh on the eyes.

Blizzards combine heavy snow with strong winds that reduce visibility to nearly nothing.

Thunderstorms form when warm, moist air rises quickly into colder air above it.

Hurricanes are huge rotating storms that draw their energy from warm ocean water.

Tornadoes are narrow, rapidly spinning columns of air reaching down from a storm cloud.

The calm center of a hurricane is called the eye and is surrounded by fierce winds.

Monsoons are seasonal winds that bring long wet spells to many tropical regions.

Droughts develop when a region receives far less rain than usual for a long period.

Heat waves are stretches of unusually hot days that can persist for a week or more.

Fogbows are pale rainbows made when sunlight passes through tiny fog droplets.

Rime ice builds up on surfaces when freezing fog droplets settle and harden in wind.

Chinook winds can warm a cold mountainside quickly as air sinks and compresses downhill.

Weather describes what the air is doing now, while climate describes long-term average patterns.

Air pressure drops with altitude, which is why mountain air feels noticeably thin.

A cold front forms when a mass of cold air pushes under warmer air ahead of it.

Warm fronts move slowly and often bring long periods of steady gentle rain.

Weather vanes point into the wind, showing which direction the air is coming from.

Sailors long watched red morning skies as a rough sign of storms approaching later.

Fog is simply a cloud that has formed at ground level instead of high above it.