shall (aux. v.) use when there is implied intention example: I shall return! not: It shall be warm at the beach.
Also use “shall” for asking questions in the first person (I or we). example: Shall we dance?example: Shall I call you?
Use of “shall” in the second or third person implies a command or threat. example: You shall stay here until I say otherwise.
will (aux. v.) to intend to example: I will go to the grocery store tomorrow.