In the season six finale Daenerys is sailing for Westeros with her army (consisting of the Unsullied, the Dorthraki and three dragons) and her allies the Greyjoys, the Tyrells and the Martells (Dorne).
The Unsullied and the Dorthraki look like they're dressed for a beach party. Is it really a good idea
to bring an army that is not used to winter conditions (such as blizzards, freezing rain, or extreme wind chill) to Westeros at the start of the winter?
Also there is the matter of provisions for the people and the horses. Her allies, however wealthy they are, probably'll need those supplies for the long winter ahead for their own people.
What were the consideratons to start a military campaign in these conditions instead of waiting out the winter in Essos and attacking in the spring, even if it takes years? Why did Daenerys and her advisors decide that winter is the right time to conquer Westeros?