@Vladenschlutte It definitely had more than 3 times go below 0F in the last nine years. There are probably even more than 3 days with windchill below -20F that Ann Arbor Public School closed in the last 9 years.
Even just for January, there were 4 years within the last 9 years with lowest temperature below 0 and it is likely to have multiple days within those year with sub zero temperature. For February, 5 of the past 9 years went below 0.
http://weather-warehouse.com/WeatherHistory/PastWeatherData_AnnArborUnivOfMi_AnnArbor_MI_January.html
http://weather-warehouse.com/WeatherHistory/PastWeatherData_AnnArborUnivOfMi_AnnArbor_MI_February.html