How the spell works is a wonder of mystery.

Due to magical weather in Oerth, the results may seem to be too harsh or severe to us, but that is nature of weather as depicted in TSR 1015 World of Greyhawk Fantasy Game Setting 1015 Boxed, 1983.

Charts and backround info, all is there. Some modernisation has been made, but the originality of Gary Gygax has been preserved.