تَأَخَّرَ الْبَرِيدُ. انْقَطَعَ الطَّرِيقُ بِسَبَبِ الْمَطَرِ. وَلَمَّا صَفَا الْجَوُّ وَصَلَ.
The mail was delayed. The road had become blocked because of rain. When the weather cleared, it arrived.
The opening announcement naturally raises the question, Why was there a delay? The next clause supplies the explanation. The third adds the later sequence of events; it is not merely a reinforcement of the statement about the blocked road.
Rhetorical analysis needs clear clause boundaries. The absence of a conjunction in one place may be explained by an implied question and answer, while the conjunction in another marks the subsequent development of a narrative.