Never mind the fact that you've decided to go outside and ride bikes or play tag instead—Call of Duty: Modern Warfare 3 will still attempt to lure you back in doors with a new multiplayer mode and a handful of tweaks.
The biggest addition is the brand new Drop Zone game mode where teams fight to control a... wait for it... drop zone in which a care package will drop every 15 seconds. That seems like an awful lot of care packages. Teams earn 20 points per team member in the drop zone every second. Kills are worth 50 XP in this mode. The catch is that pointstreaks are disabled unless you pick up many of the care packages.
Infinity Ward, Sledgehammer Games, and Activision have also tweaked Hardcore game modes so that any damage you do to your teammates, which would normally result in killing them, will now richochet onto yourself, so choose your shots wisely.
Or... you know... resist the urge and go play in the snow.