The simplest kind of weather station for KS1
Make pine cone weather stations with your class, and see how well they do at telling whether it is raining or not!
More experiments and demonstrations

Experiments with an Infrared Thermometer
Infrared thermometers can be used to explore a range of questions.

What is the Dew Point?
The dew point is the temperature at which, with a given amount of water vapour in the air, water vapour will condense to form cloud droplets, if particles are present for the droplets to form on.