How Weather Works

Req 5 — Wind, Rain, Lightning, and Hail

5.
Tell what causes wind, why it rains, and how lightning and hail are formed.

This requirement gets to the moving parts of weather. Instead of memorizing vocabulary, think about what the atmosphere is always trying to do: balance differences in temperature, pressure, and moisture. Wind, rain, lightning, and hail are all results of that constant movement and energy transfer.

What causes wind?

Wind is air moving from one place to another because of differences in air pressure. Air tends to move from areas of higher pressure toward areas of lower pressure. The bigger the pressure difference, the stronger the wind can become.

Pressure differences often start because the sun heats Earth unevenly. Land and water warm at different rates. Dark surfaces absorb more heat than light ones. The equator receives more direct sunlight than the poles. As air warms, it becomes less dense and tends to rise. Cooler, denser air sinks and moves in to replace it. That movement is wind.

Other factors matter too:

Why does it rain?

Rain starts with water vapor in the air. When warm, moist air rises, it cools. Cooler air cannot hold as much water vapor as warmer air can, so the vapor begins to condense onto tiny particles in the air. That creates cloud droplets.

As those droplets collide and grow, they become heavy enough to fall as precipitation. If the air is warm enough from cloud to ground, that precipitation falls as rain.

Rain commonly forms when:

What Creates Weather? (video)

How lightning forms

Lightning forms inside storm clouds when strong updrafts and downdrafts move ice particles, water droplets, and hail around violently. Those collisions help separate electrical charges inside the cloud. Over time, the difference in charge becomes so strong that electricity suddenly discharges.

That discharge may happen:

Thunder is the sound made when the lightning channel superheats the air so quickly that the air expands like a shock wave.

What Causes Lightning? (video)

How hail forms

Hail forms inside strong thunderstorm clouds, especially ones with powerful updrafts. A small ice particle gets carried upward into very cold air, where liquid water freezes onto it. The growing hailstone may fall, then get lifted again by another strong updraft. Each trip adds another layer of ice.

When the hailstone becomes too heavy for the updraft to support, it falls to the ground.

That means large hail usually tells you the storm has very strong upward motion.

What is Hail? (video)

A simple way to connect the four ideas

Weather eventMain cause
WindAir moves because pressure is different from place to place
RainMoist air rises, cools, condenses, and droplets grow heavy enough to fall
LightningCharges separate inside storm clouds and discharge suddenly
HailStrong storm updrafts lift ice repeatedly so it grows in layers

How to explain this to your counselor

Try connecting each process to a picture in your mind:

If you explain the causes instead of only naming the events, your answer will sound much stronger.

The next requirement helps you read one of the easiest clues weather gives us: clouds. Once you know their levels and shapes, the sky becomes a forecast tool.