You can find more information about the City Council adopted policy for filling an Aldermanic vacancy in Ordinance Section 2.04.020. You can find more information about the State of Wisconsin Statute that governs Aldermanic Vacancies in 17.23.
Per 17.23 of the State Statutes, “unless ordered by the common council, a successor shall be elected for the residue of the unexpired term on the first Tuesday of April next (2019)…..”
Thus, the appointee will serve from the date of appointment in 2018 to April 2019, and will then have to run for the remaining year of the term. Since the vacancy is not occurring before June 1 in the year preceding expiration of the term of office, a special election cannot be ordered on the Tuesday after the first Monday in November following the date of order.