Can the forecast N+1 days ahead be more certain than the forecast N days ahead?
Typically, days with conditions which might produce local instabilities would produce a less certain forecast than a day with a stabilize pattern even if the more stable day was further in the future.  For instance, tomorrow may have the potential for localized disturbances some maybe there will be thunderstorms, maybe they will not form.  But two days later, a large high pressure zone will almost certainly clear everything out or a band of rain will definitely reach the area.