Over the years I have learned that even when you think it won't rain, it does. Rain is lovely if you are inside, listening to the drops fall while sipping a lovely cup of tea. Rain isn't so fun if you are on a trip and want to visit a museum, go to a shop, or dine at a restaurant because most of the time you will be walking and you don't want to arrive completely drench.
Stick a small collapsible umbrella in your luggage or your carry on. These compact types are easy to throw in a backpack, purse or tote bag. You won't regret having it along when those skies open up.