According to the 2017 Time Off Program Guide: [A]ll unused vacation accrued after January 1, 2016, will be forfeited unless you work in California, Colorado, Illinois, Massachusetts, Montana, Nebraska, North Dakota, or Rhode Island, or employment ends due to retirement or death. If you have any unused vacation prior to January 1, 2016*, that vacation will be paid to you upon termination—regardless of the state in which you worked or the reason for which your employment ended.
Like HRZone said, see HR to see if you can use vacation hours for previous weeks.