L'imparfait et le passé composé

Bonjour Love F,

"Le Passé Composé (Indicatif) is more like a direct equivalent of the English Simple Past (I went, I did ...).
It is used for past actions/events that happened once, with a clear beginning and end, as well as for a succession of actions in the past."

The above is taken from the lesson.

The fact of it having rained in the period Monday to Friday is an action completed, as described in the lesson above, "a clear beginning and end"

This is why the passé composé is appropriate.

Bonne journée

Jim