Ash is what remains after fire, so tradition reads it as an ending, loss and the residue of something past. In old symbolism it is also the ground from which renewal rises, like the phoenix. Ash falling from the sky is usually read as grief or the aftermath of a major change. Sifting through ashes is linked to searching for what can be saved, while scattering them points to letting go and closure. Ash on the face or body stands for mourning or humility. It can help to ask what has ended and what might grow there.
Does the traditional reading fit your dream, or did it mean something else to you?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.