？
I wonder what tomorrow's weather is going to be like?
Literal
Tomorrow [possessive-の] honorable-weather [topic-は] how [wondering-かしら].
かしら is a distinctly feminine sentence-final particle expressing wondering or doubt — the female counterpart to the masculine かな. Usage is stereotyped in fiction but still alive in older or genteel women's speech. お天気 uses the honorific prefix お, which is often attached to weather, food, and other everyday things in women's speech.