It was two full days of closure. I have two concerns.
1) We do not have PTO, we have vacation time, sick time and personal time. All three are addressed in the employee handbook and have rules associated with them. Sick time is the issue here. Some employees have only sick time left as they are required to use all vacation before a blackout period, or lose it. Sick time rules state that it can be used only for sickness. So can we now ignore that policy and deduct time from the employees banks to cover these two days?
Here's a path to thinking about your policies that should help you arrive at an answer.
Do your rules permit the employer to force vacation use or say the employer cannot or will not force vacation use?
Why would you make an exception for sick time? Would you want to make a habit of using sick time to pay for weather closures in the future? Does your handbook specify that policy statements are broad, intended to be interpreted broadly to give management discretion to address a wide range of workplace issues? Does your handbook reserve the right to modify policies on the fly?
2) During this two day closure, employees were instructed through our employee website and our emergency phone number to check every hour for updates. Were they essentially on call?
That one is harder. The issue is whether your employees were waiting to be engaged or engaged to wait. In the latter situation, they must be paid. The issue is whether they were able to do as they wished with their time. If yes, then they weren't on call. If they were required to check in every hour or if they were required to be ready to come to work on a moment's notice, then they were probably on call and you would have to pay them, but not necessarily at their normal rate.