When it's raining out, it's probably not a good idea to walk in front of moving traffic in the hopes that they'll stop for you.
When it's raining out. Visibility is bad. Ask yourself, can this driver see me? Can the driver even see the crosswalk?
When it's raining out. It takes longer for a vehicle stop. Stepping into a crosswalk twenty feet in front of a car that's moving at 30 miles an hour isn't smart regardless of how you do the math.
Whether or not it's raining, it's probably not a good idea to just decide you're going to walk in front of a moving vehicle a) if you haven't made eye contact with the driver b) if the crosswalk isn't marked or c) driving conditions are less than ideal.
You're life is probably more important than being right. But I suppose that's something you have to ask yourself.