Thanks! Usually, it is just for a few hours during nighttime or early morning. Ice days where temperatures do not rise above freezing measure 1-5 per year, frost days around 30. Ice days are most times isolated, but this february there were three in a row. But in its northernmost habitats in Miyagi prefecture, multiple ice days can also occur in a row.
A usual frost day has minimum -2C at night (28F) and arond 40F or 5C from noon to sunset in my area.