60:3 The bracha one recites on thunder and/or lightning covers him so long as the clouds of that storm have not been dispersed. If the sky brightens in between thunder claps or lightning flashes, one would recite a new bracha. (If it is continuously cloudy over the course of multiple days, one would recite the bracha on a subsequent day – Mishnah Brurah 227:8.) One does not recite a bracha on heat lightning, which is lightning that one might see on the horizon, unaccompanied by thunder.
60:4 Upon seeing a rainbow, one recites a bracha to the effect that G-d remembers His covenant, is faithful to the covenant, and that He keeps His word. (See a siddur for the actual text.) We are not permitted to stare at a rainbow (and we should not point them out to others – MB 229:1).