You may not realize it, but this is still Switzerland despite tropical temperatures last night.

Locarno saw overnight temperatures of about 21.4 degrees, with Lugano, Zurich and Lucerne logging about 20 degrees. 

The reason for the heat wave was subtropical air from the South and not the Föhn weather phenomenon that brought the heat in April.

The warm front comes ahead of the longest day of the year, beginning early Thursday, with the astronomical start to Summer.