Fitzgerald uses weather to demonstrate the mood in this chapter. It begins with rain, and once the relationship between Daisy and Gatsby appears secure, the sun comes out.
The mood of this chapter varies greatly. At first, it feels insecure. So, as Daisy is about to arrive, Gatsby looks at the time and at 2 minutes until her scheduled arrival, he gets up to go because he believes she is not coming. This is a character action that is used to demonstrate insecurity.
Once there, Gatsby almost refuses to talk to her. He was not in the room when Nick brought Daisy into the room. Then, he comes and knocks on the door and acts awkward for quite a few minutes. In an effort to relax, Gatsby leans against a clock on the mantle knocking it over. He catches the clock though and sets it back up. This ironic moment demonstrates Gatsby playing with time. This again, is a sign of insecurity because he hits the clock out of nervousness. In a quick discussion with Nick, Gatsby reveals how he thinks this is not a good idea. Nick leaves the two alone.
Nick is absent for whatever reconciliation occurs so the reading audience does not see it.
Nick returns when the sun comes out, and their relationship then seems sealed. I would argue that Fitzgerald uses weather, symbols, irony, and character actions to help create mood.