Technically ... Shall can really only be used with I. One can't speak for others.

Will means intend to.
Shall means actually going to do it, no hedging about intentions.

A parent can say You shall to a child, but the kid still might not. So, twchnically, not proper usage.

It shall rain? Hmmm. Presumptuous, kinda.

Not that this is common current usage, I do know.