Future perfect (will have + past participle) is primarily used to describe an action that will be in progress at a specific moment in the future, without considering its completion.

In first conditional sentences, "will" is required in the "if-clause" to indicate that the condition being discussed is a logical certainty that the speaker fully endorses in formal English grammar rules.

The modal verb "will" is the standard form for expressing intentions based on present evidence, such as observing dark clouds and predicting rain within the next few minutes of the discourse.

The "present continuous" is used to describe future arrangements or fixed plans where a specific time and place have been agreed upon, usually involving more than one person or an external organization.

The structure "be going to" should be used to express spontaneous decisions made at the exact moment of speaking, especially in response to an unexpected request from the interlocutor during conversation.