How Do I Account For Seasonal Fluctuations & Vacancies?

[Zackarias Aitchison]

Hey! 

I'm looking at purchasing a property that I'd turn into an AirBnB in a skiing town. 

During the long winter months here in Canada, the AirBnB will be rented out for sure, 

But how do I account for the slow summer months or even unpredictable vacancies in my expense calculations? 

Thank you in advance, cheers!