Quick advise please!! How to convince my mom to let me go to my boyfriends?

Okay, so i need quick advise. My mom wont let me go to my boyfriends house because of the snow. Yesturday she said it was fine, but today she decided to change her mind. My boyfriends dad offered to pick me up and bring me home later, but my moms being a *****. She says if shes stuck here then i have to be too. She let my sister have two friends over, but wont let me go to my boyfriends. The only reason why she changer her mind is becaause shes pissed at my sister, and when ever shes pissed at my sister she takes it out on me because my sister is out of control. Any ideas how i can convince her to let me go to my boyfriends?