The Autumn Thanksgiving one starts on November 27, the Winter one begins on December 19
The start and end dates of the Steam Autumn Sale 2013 and the Steam Winter Holiday Sale 2013 have been leaked online thanks to an official email from Valve that was just sent to developers from around the world, notifying them of the two big promotions.Valve has just held its traditional Halloween sale on the Steam service and already users are looking forward to the next big events: the Autumn (Thanksgiving) and Winter (Holiday) sales.
While the start and end dates of these promotions are usually kept a tight secret by Valve and its development partners, it seems that an email with these actual dates has been leaked online, via Reddit.
Apparently, a Russian developer has just been notified by Valve about the two upcoming promotions and he posted a screenshot with that message online, which you can admire above.
More specifically, the Steam Autumn Sale begins on November 27 and ends on December 3.
The Steam Winter Holiday Sale starts on December 19, 2013, and ends on January 2, 2014.
As such, prepare to take advantage of quite a few different deals during those periods.