Cities: Skylines 2 will launch with some great features the previous city builder sold as DLC

gamesradar.com:

The Cities: Skylines 2 devs have just dropped a fresh round of details on the game's climate and weather systems, and it looks like some of the best features from the previous game's DLC are going to be included here as part of the base experience.

Cities: Skylines 2 has a day-night cycle that ties closely with its new season system. At the default game speed, 24 in-game hours translate to just over one real-life hour, and three in-game days will see the passing of an entire season. Seasons will determine the likelihood of certain weather effects, and in winter you'll need to be sure to invest in road maintenance infrastructure to keep your roads from turning into icy hellscapes.

The weather also determines the likelihood of certain natural disasters, three of which are detailed in the latest dev diary: forest fires, hail storms, and tornados. You can mitigate the effects of disasters somewhat by building emergency shelters and early warning systems, but each type will have its own specific effects. There's no info on whether there will be more than those three disaster types in the base game, however. 

Many of those features will sound familiar to anyone who's invested in Cities: Skylines DLC in the past. Natural disasters, a staple of city-building games going all the way back to the original SimCity, were added as part of the aptly named Natural Disasters pack. While it was a free update, day-night cycles were only added around the release of the After Dark expansion. Snowy conditions were added as part of the Snowfall DLC, though the sequel is one-upping that by not just including winter maps, but proper changing seasons.

Maps will still determine your climate and weather to a certain extent, as each map is divided