My first section on photography tip. A question that I googled before myself when I was still new in photography. I always worry what will happen to my gears. Here are some of my real life encounter. Hope it helps you when you see dark clouds out there.
It has been raining cats and dogs this month and it has not spoil my mood to shoot at all! I will just wait it out as I always believe before and after a rain is always the best time to shoot portrait sessions or sceneries. Why? Cause it has blue sky, fat clouds with yellow sun appear behind those clouds which can cause more dramatic sky than any normal day. I just assisted George Yong again today for the 3rd time showering under the rain with Nikon D300, D90, Flashes and Lenses wet under moderate rain. The kind that really wet the whole gears and us as well. We just need to trust our equipments and Nikon did a good job under the rain. Bring another umbrella just to protect some of the lens that you not yet ready to shoot.
One tips that I want to share with you all is make sure after the raining shoot, wipe your gears and use blower and wipe again. Then keep in an air conditioned room if you do not have a dry box to keep in. Just be careful when you wake up don’t directly take out your cold camera out of your room as it can cause condensation. Leave it in your camera bag and let it acclimatized to outside room temperature before use again.
You know what, the sunset or the sky are even more dramatic after the rain. We just need to persist and believe that there is always hope. Remember guys, if you see those dark clouds do not keep away your cameras. Just drive out under the rain and reach to your destination. You will never know what silver lining is waiting for you.
*ps- the shots below taken with my wet iPhone too 
See how the colour changes in one sunset!! From yellow to purple to blue. No editing at all.
p/s- My first Sony W-1 Compact Camera Died because I used it under the rain in the jungle. So it all depends on your camera models and lenses durability against rain drops.