Study Fig. 7, an extract from the diary of a sailor. As we left the harbour at 09.00 hrs on the 29th July the sky was almost clear, with just a few wispy, feather-like clouds. There was a strong westerly wind, but the temperatures were warm. By 14.00 hrs the wind speed had dropped and it was blowing from the north west. Temperatures had fallen several degrees and very tall, dome-shaped clouds with dark bases had formed. The visibility was getting less. As the rain started to fall we sailed back home but by the time we reached the harbour we were very wet. [Figure 7]