It seems that DL has been a bit disingenuous with trying to make passengers take credits instead of refunds for cancelled flights. Even if the flight was cancelled for weather related reasons, OP is absolutely entitled to a refund.

A friend recently had a booking on DL’s PVG-SEA flight when all DL flights for the week on that route were cancelled (presumably due to a Chinese government regulatory issue with imported COVID cases?). Due to the sheer lack of flights between PVG and the US these days, DL did not offer rebooking as an alternative- and tried to make him take a credit instead of a refund.

I told him he absolutely needed to push back, but he had a lot of other things to deal with at the time in trying to escape COVID lockdown in Shanghai, so I’m not sure what he ended up doing.