Because of Spa's location in the middle of the Ardennes Forest, the weather can change in an instant. It can go from bright sunshine to pouring rain in minutes.
Teams know what the weather can be like at the Belgian GP and are prepared for this. But, it certainly helps to spice up the action and you never know what's going to happen!
Another factor is the length of the circuit at Spa. It's the longest lap of the year, at 7.004km, which means weather conditions can be completely different at separate parts of the circuit.
So, for example, it could be raining at La Source, but be bone dry at Les Combes or Pouhon.
At the moment, some rain and cooler temperatures are expected for Friday, Saturday and Sunday. But as we all know, you should never fully trust weather predictions for the Belgian GP.