Here's the policy I have been using for classes:
Weather policy: If the weather is such that it jeopardizes the students' safety, the class will be postponed or delayed as appropriate. Otherwise, the class will go forth as scheduled rain or shine.
Cancellation Policy: The deposit is non-refundable if you choose not to attend the class. If I am forced to cancel the class for reasons other than the above outlined weather policy, students will have the option of refund of their deposit or attending the course on another date at a reduced fee.