The airlines do not have to compensate for weather, only mechanical. When it is a major storm like the ice storms earlier this year they allow flyers to change their travel dates before or after the storms but they put advisories out to that affect. There is no such statements currently on the delta website only this

Advisory: Upper Midwest Weather
Winter weather is expected to impact travel to, from, and through the Upper Midwest U. S. on Feb 20-21, 2011. Check flight status frequently for up-to-the-minute info about your flight plans, or get updates sent directly to your wireless device or email with Delta Messenger.

You can call and try to get a refund but I doubt it will happen.