Quick keys to success:

Never leave the house during the spring without rain-resistant/proof gear.

Remember that the percentages given by weather forecasters are just another way of saying "... for all X number of days in the past when conditions were similar, or nearly the same as today, it rained on Y amount of those days." Y/X is your percentage, which means damn near nothing.

Live by doppler radar images. Loop them multiple times if you have to, and calculate how fast the system is moving.