I have a seasonal property (ski on/off) and have had situation with weather. There are several things to consider...
1. A renter could always take out insurance to cover the possibility of a natural disaster or poor weather.
2. You are in a service business and you want to be able to capture all revenue. I have offered guests a credit towards a stay at a later date.
3. You can agree to mitigate (which you have a responsibility to do), where you re-list the unit and if it is rented you will refund them, (it's tricky on ABB, but I have done it with Paypal).
4. Do a hybrid, have them come and stay and give them the option to leave early if conditions do not improve.
You have no obligation under your policy to issue a refund, but ABB may consider it an extenuating circumstance and refund anyway.