I wondered this myself as the adult pair I got off a guy last year apparently only mated for him when he put one of those Exo Terra waterfalls into the viv, which upped the humdity drastically.

However, I've had no probs breeding them without the waterfall, and suspect he didn't keep them at the right humidity to start with so my case is probably different to your own.

How long have you had them together? If it's only a recent introduction, it could just be coincidence that you seen them courting when a storm was on it's way.