Final answer:
The first five words of the weather proverb 'Rain long foretold, long last; short notice, soon past' refer to the formation of cumulonimbus clouds, which are associated with thunderstorms and heavy rain.
Step-by-step explanation:
The FIRST FIVE words of the weather proverb 'Rain long foretold, long last; short notice, soon past' refer to the formation of cumulonimbus clouds. Cumulonimbus clouds are associated with thunderstorms and heavy rain, so the proverb is suggesting that when the signs of rain are observed for a longer period of time, the rain will last longer. On the other hand, when there is a short notice of rain, it is likely to pass quickly.