Weather - what causes it?

All weather on earth originates with the sun.
Start by setting up the heating land and water activity. Allow to run for at least 10 mins.
While it runs, do the sun's angle on earth activity.
From the results of the heating land and water activity, and conclude that sand heats up faster than water. On earth the land heats up faster than the oceans.

Summarize the effects of the sun on the earth: the sun heats up the earth, but it heats it unevenly - the equator is heated more than more northern or southern latitudes (because of the angle of the sun's rays), and the land is heated up more than the water (because the land heats up more quickly).

Question to students - what colour reflects light more - light or dark? Snow and ice reflect the light and the heat, whereas the darker forests absorb the light and heat, so are heated up more. The sun is also unevenly heating up the darker and lighter areas of earth.

The land heats up the air above it, and the result of the uneven heating of earth is that some areas will have warmer air and some areas cooler air. These warm and cool air masses will interact.

The warm/cold/salty water flow activity models how air masses interact when some are warmer than others. It will also model how the water in the oceans moves around, when some parts of it are warmer or colder or more salty.
Once students have done the activity, summarize it:
In the atmosphere, this movement of warm air upwards and cooler air downwards generates winds.
In the oceans the movement of colder and saltier water downwards and warmer water upwards generates ocean currents that moves heat with them and affect the climates on land.
A simpler demonstration showing how warm water (and air) rise is the convection demonstration.

So the uneven heating of the earth means that air and water moves around, generating global winds.
Show an image of the global air circulation patterns showing the air rising at the equator and falling further north and south where it has cooled (e.g. https://en.wikipedia.org/wiki/Hadley_cell#/media/File:Earth_Global_Circ…)
These winds can carry rain or clear skies to different parts of the earth. Show a live interactive map of Earth’s winds across the surface: https://earth.nullschool.net/#current/wind/surface/level/orthographic=-…

The air masses do not move in straight lines.
If fast moving air meets slow moving air, or if air moves over a mountain range, the air will start to make swirls and eddies - called turbulence.
Do the turbulence activity.

One more phenomenon that is vitally important for making air move from place to place.
Ask students to do the air pressure in a bottle activity and figure out how it works.
Afterwards, summarize: air moves from high pressure to low pressure, creating winds and moving rain from place to place.