The speaker starts with ordinary rain outside, but it quickly becomes a way of talking about what's going on within. Their head is full of feelings, and all of them turn out to be sad, which leaves them wondering whether the world is really that cold or whether they're just overthinking it.
The middle of the poem blurs the line between weather and emotion. The speaker asks why tears are running down their face if the rain is outside, and why thunder seems to crackle where no one else can hear it. The nervous "Haha!" suggests they're brushing off their own question, almost embarrassed. By the end the real rain has stopped, but the thunder hasn't. That detail carries the poem's main idea: sadness can linger long after the reason for it has passed, and it's often invisible to everyone else. The mood is quiet, lonely, and confessional.