I live in Central Coastal California and am just starting my veggie/flower garden, it is my second year. I typed in the question are snails more active in the rain and the answer is YES! Especially the foggy, warm rain we have in this area. I use Sluggo and it works OK but has to be replaced after being wet too many times. The best solution is to go snail hunting, I just got back from my garden and I found tons of snails & slugs, it’s around 6 am here & rainy. The main thing I’m doing to combat the problem is planting flowers they aren’t attracted to (nastursiums & impatiens) and starting all my seedlings at home. I learned a hard lesson last year about seedlings and snails, I had them wipe out entire crops. Now I’m getting good, strong seedlings to plant and that seems to help the most. I’m also not planting flowers they actually like like cala lillies, snails & slugs love to hide in their foliage.