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"What's added with Seasons is dynamic weather effects that you'll actually see transition seamlessly throughout the year," explains Mike Zamora, a Producer with EA.
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"There are other things you can do as far as professions in the game, but I don't think we're going to go too deep into that right now," commented Zamora
The expansion will be compatible with all previous The Sims 3 expect for World Adventures. The rational being that it wouldn't make sense for it to snow in locations such as Cairo. That stated, the developers are doing their best to ensure that Seasons will flow with all of the others.
"We looked at all of the expansion packs that we have and we said how are we going to get weather to work for everything," the game producer said. "That's what we wanted to do. We didn't want to do anything less than that."
The Sims 3: Seasons is expected for release on November 13. Being an expansion, it will require the core The Sims 3 game in order to play.
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Source 1 and 2
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So I only recently got over the pudding faces in The Sims 3