To show how wind vortexes work to form tornadoes, all you need is two two-liter soda bottles, duct tape and a room of eager children. Fill one bottle two-thirds full with water, then duct tape the spout of the bottle to the spout of the second bottle. Make sure the bottle is tight so water doesn't leak. Another way to fasten the bottles is with a Tornado Tube, which can be ordered online and are made for this experiment. Turn the now-connected bottled upside down so the water is on top, and swirl the bottles one direction as the water falls. The motion will form a water vortex as the liquid falls, which explains the natural motion that causes devastating tornadoes from winds as pressure systems shift.
To explain to children that lightning is simply electricity built up in the atmosphere, all you need is a fluorescent light bulb and a balloon. Blow up the balloon and rub it against your hair for about a minute. Then, turn out the lights so the room is as dark as possible. Touching the balloon to the end of the fluorescent bulb will light the bulb. You can teach the fascinated children that rubbing the balloon against your hair created an electrical charge, which is what pressure in the atmosphere does when thunder is heard. The lighting is the release of that charge, which the balloon does through the light bulb.
When it snows in the winter, gather some fresh show in a container and measure its height with a ruler. Then, when the snow melts, children can learn that it is made of frozen water. Record the water's measurement and repeat the steps throughout the winter to compare different kinds of snow. Kids will be fascinated to see that the same height of snow can have drastically different amounts of water due to various environmental factors.
On a sunny day, bring a glass full of water outside. Put the glass on the edge of the table so part of it is hanging over the edge. With the sun shining through the glass of water, place a piece of white paper on the ground so the sunlight hits it and adjust it until a rainbow is visible. This explains that light is made up of many colors, which are visible when the light beam passes through water, as when it rains.