Pattern Select Switch Snow Mode Circuit [04/2013 - 08/2015]: Description
WARNING: This page is about a different car, the 2015 Lexus IS 250 and 2014 Lexus IS 250. However, it is still accessible from the selected car via links, so may be relevant.
When SNOW is selected, the operation of the throttle motor is moderated to control engine output. This helps to reduce skidding of the drive wheels, and assists with takeoff acceleration, driving straightness and turning stability.