The development update for Crusader Kings 3 (PCG's 2020 strategy game) details the changes in the 1.3 update. The season will have three different severities, depending on geography, which will affect armies in different ways.

The more severe the winter, the more snow, and the more supplies any army will consume over time. Snow slows movement, and sometimes blizzards make the situation even worse, plus battles become more deadly for both sides.

Most affected are cavalry units, especially heavy cavalry, which suffer heavy penalties. It is not a good idea to fight in the mountains on horseback in the winter. Other types of troops receive a bonus when fighting in winter: "They are accustomed to the cold and snow of the mountains and can take advantage of it in the form of damage bonuses whenever they take part in a battle where winter is present.

In addition to this, the 1.3 update will reorganize several existing territories, including the Emerald Isle. Apparently "the Irish barony was a bit too large" and therefore "significantly less densely held than its neighbors England and Scotland. The western half of Ireland in particular suffered from rather large baronies. To solve this problem we added several new baronies, along with several new counties.

Patch 1.3 for Crusader Kings 3 will be released alongside the game's next DLC, which has yet to be detailed but will be introduced at the Paradox Insider presentation on March 13.