Our mild winter (so far) has been punctuated with what we called in Texas (where I grew up) 'blue northers.'
We don't use that term in the Southeastern U.S. where I live now -- 'cold fronts' is about as colorful as it gets.
But basically it means the same thing, a wave of much colder air bringing much lower temperatures. Tonight, in the mountains, it may reach 19°F. Chilly, especially if there's wind, as we usually have.
My cold season veggies look forlorn, even those under cover of minimal plastic, and glass. But there are birds to watch and tomatoes and peppers to order, so all is fine!