I did this on the first event that didnt have a triangle (blizzard warning)
- Go to the event and blueprint it if you want
- Make sure you choose a type where you can use a car you doesnt have snow tires on
- Choose your car without snow tires (It might ask you if you are sure you want it say yes)
- Set the AI on lowest difficulty in the prerace screen
- And then just win the race (i did it in GTR HE)
Its pretty easy except the last corner is a bit tricky if you go in to quickly so i recommend having rewinds turned on and to brake a lil earlier for corners thenyou usually do
Edit: Doesnt unlock for some people when using stock tires. But does if you switch them to street.