must (be)...
This pattern is used to express expectations or assumptions about a particular situation that is considered logical.
Examples
仕事が終わったはずだ。
He must have finished work.
今日は寒いはずだ。
It must be cold today.
彼女は学校にいるはずだ。
She must be at school.
Quick check
今日は寒い___。