Go to Google (or your Google search bar), type 'let it snow' and hit enter. SURPRISE, it starts snowing and the screen starts to frost over. Then, once it's completely frosted YOU CAN DRAW IN IT. Just wait till you tell your mom -- she's gonna get such a kick out of this!
Thanks to brianna, Jason, The Grinch (get outta here with your little-ass heart!) and Court, who still make it snow the old fashioned way: praying it won't so their flight isn't canceled. Works every time!