for much of the country it s a very good night to be inside. in the north, lake-effect snow is burying areas around the great lakes, an arctic air from canada is bringing uncommon cold all the way down to the deep south. a look at the low temperatures, records in some places, tells only part of the story. mark strassmann is in the heart of florida s citrus-growing country and, mark, farmers there are understandably worried tonight. reporter: they really have to be, katie. these. 70% of these groves supply america s citrus and these crops are now in a real desperate fight for survival. it s part of the deep freeze that grips so much of america. in wintery central florida, citrus farmers were frozen by fear. john arnold s crop faced ruin. well, we haven t slept in a day and a half. reporter: that s scary. yeah. reporter: overnight, freezing temperatures menaced the state s billion-dollar citrus crop, two thirds of it unharvested. but good news. so, for instance, this,