The weather roll was a 1, which in May/June means it is simply awful. Except in the Arctic and the Mediterranean weather zones, planes are grounded.
Only the USSR feels it can get by, what with the nice burst of late-spring snow.
Edit: I have posted an image showing the weather overlay. You can see snow in the Arctic zone, storm in the North Temperate zone, and just a fraction of a sea hex with its lightning bolt weather. (Other screenshots with more horrible weather sure to follow.)














