When it rains, you have to take the wind and the distance you have to go into account to see if it is better to run or to walk. Thus, as a rule, when it rains but is not windy, it is better to walk if you want to get less wet. In the same way, if it is raining and windy, it is still better to walk. But if it is raining and windy and you only have a short distance to go (less than 150 meters) you will stay drier if you run!