Cloudy Gray Runechalk

Chalk One Up. Anything you draw or write appears in the sky as clouds A strong wind can blow the clouds away early, or they dissipate naturally after one hour. A single message can consist of a maximum of 20 characters or one symbol. You can use the chalk 20 times before it runs out.   You do not need to be able to see the sky. However the message will not appear if the magic can not reach the sky. This happens if there is 1ft. of stone, 1 inch of common metal, a thin sheet of lead, or 3ft. of wood or dirt between the surface you wrote on and the sky.