A less subtle version of the message spell, skywrite creates words in thin cloud formations above a point chosen by the caster. One word per caster level can be created; the words are spelled out one letter at a time at the rate of ten letters per round. The spell must be cast in daylight so that the white cloud letters can be seen; it does not work against a cloudy sky.
The letters appear about 100 feet above the ground and are each 10 feet tall. Everyone below the skywritten message can see what it says; this could be an entire city. Of course, the caster has no control over the actions of those seeing the message, so judicious choice of words is recommended. "Attack enemy's right flank" probably is not a wise message, nor is "Treasure below statue in town square"—unless the caster wants to mislead an enemy or wreak havoc.
While the spell is active, the clouds remain in place, despite strong or even magical winds. They are harmless and insubstantial. When the spell's duration expires, the clouds begin to filter away on the wind, slowly dissipating to nothing.
The spell requires chalk and a slate, upon which the message is written. If the caster is interrupted in his writing, whatever portion of the message was written appears in the sky. "Attack us at your peril" would be an entirely different message if interrupted after the second word.
Notes: Rare spell from the Forgotten Realms setting. Known to be in Myrl's Text.