The phrase "crummy weather" means that the weather is not very good or pleasant. It refers to conditions that are undesirable, such as rain, storms, or extreme cold. Full definition
The elastic straps that cross over the top of the foot keep the flats in place, which is incredibly handy for commuting during rush hour and in all types of weather — nothing is worse than having your shoe slip off during a mad dash for the bus in crummy weather! (testfacts.com)
With this kind of crummy weather we've been having (here in the Northeast anyway) what better time is there to fantasize about taking a road trip?? (thefemininefiles.com)
But a business can also build its brand around crummy weather as well. (entrepreneur.com)