The moisture laden winds strike the mountain and cannot cross the mountain. They cool down as they rise along the mountain and shed their moisture in the form of rain on the same side (windward side). By the time they reach the leeward side, they are devoid of moisture or have very low moisture content. Therefore, the other side (leeward side) remains dry and is known as rain-shadow area.
Frontal rain is common in mid latitudes because it is the zone of convergence of warm westerlies and cold polar easterlies.
Convectional rainfall is very common in equatorial region around 4 o'clock as the surface gets heated up during this time. Therefore, convectional rainfall is also called 4 o'clock rainfall.