明日 と 明日

[Garyuchin]

Well, that subject line answers one question.

I have heard あした used in all cases, but あす seems only to occur in the accusative case 「あすを」.

Is あす used in other cases?

[Airth]

Yes it is. You often hear あす on the news, and you will be guaranteed to hear it on the weather forecast - あすの天気です

Apparently, 明日 should never be read as あした. And あした should always be written in kana. In the real world, it would seem that is routinely ignored.

[Garyuchin]

Gak. Completely opposite to what I was expecting. Thanks Airth.