Question

why the rainfall occurring in rain shadow area

Answer 1

this cause them to cool down which causes excess in moisture to condense into high Cloud and result in heavy precipitation over the mountain range this produces cloud and rainfall and windward side of mountain

Answer 2

This causes them to cool down which causes an excess of moisture to condense into high clouds and results in heavy precipitation over the mountain range. These produce clouds and rainfall on the windward side of the mountains, but the leeward side stays rain shadowed and extremely dry