This is not exactly your situation, but I have cancelled reservations after the cancellation deadline and had the penalty waived due to flight cancellations, delays, etc. Usually this happens within 24 hours of arrival. I have had success both through Marriott CS and calling the hotel directly (depending on if it's a points reservation or a cash reservation). My most recent success was just last week.

I would wait. If the storms get bad, airlines will start issuing waivers/cancelling flights, and you'll have a stronger leg on which to argue that your reservation should be cancelled without penalty.