In the United Kingdom and Ireland, an April shower is rain during the month of April. One of the major causes of the often heavy downpours is the position of the jet stream. In early spring, the jet stream starts to move northwards, allowing large depressions to bring strong winds and rain in from the Atlantic. In one day the weather can change from springtime sunshine to winter sleet and snow. The track of these depressions can often be across Ireland and Scotland bringing bands of rain followed by heavy showers (often of hail or snow) and strong blustery winds.
The proverb “March winds and April showers bring forth May flowers”, first recorded in 1886, or the shorter, trochaic version “April showers bring May flowers” (originally “Sweet April showers/Do spring May flowers”, part of a poem recorded in 1610) are common expressions in English speaking countries.