Traffic accidents even with road closure don't apply. You can only extend your time if it is to get to a "nearest safe haven". Dispatch is not excused for not knowing about weather. It IS THEIR JOB to know about forseeable conditions since they are in control of putting drivers on the road. Many court cases back that one up. It mainly boils down to your presentation to the officer of what your circumstances are and his/her mood when you're talking to them. Best piece of advice is DO NOT try to fudge anything on this. It's not worth your job and no employer or supervisor is going to do anything but save their own neck.