in cool days or on cool das

oncooldays. The preposition on has several typical uses:

1. To express direction. It means "on the surface of something (and in contact with a surface)".

2. Indicates the object involved, meaning "about".

3. Indicates time, before a specific year, month and day, in the morning, middle and afternoon of a specific day, or tells the weather conditions.

4. When expressing the weather in English, we can use the prepositions in and on, but the usage of these two prepositions is different. The preposition in is mainly used in the following ways: in + "typeofweather" (goodweather, badweather, rain, storm, sun, snow, hurricane, tornado, tsunami, etc). The preposition on is mainly used in the following way: on+"typeofday" (sunnyday, rainyday, coldday, hotday, snowyday, etc) so incooldays will not work.