1. Is it too late to call him.
(What does 'it' refer to in the sentence? Weather?)
"It" refers to the situation or "the way things are". "It" wouldn't be the weather, because you don't measure weather with time adjectives (such as early or late).
You might be thinking about inviting him to a meeting, for example, when there is not enough time for him to get there.
In the sentence "Is it too late to call him," the pronoun 'it' does not refer to the weather. In this context, 'it' is a placeholder pronoun that is often used when referring to a previously mentioned situation or event.
To determine what 'it' refers to in this sentence, we need to consider the context surrounding it, which is missing from your question. Without that context, it is difficult to accurately determine what 'it' is referring to. It could refer to a specific time, an action, an opportunity, or something else that was previously mentioned.
To understand what 'it' refers to, you would need to provide more information or provide the broader context of the conversation or situation in which this sentence was used.