My definitions of temperature, depends on season, if it is going into or coming out of winter
Winter is coming: first day with highs around 35 F.
Cold, highs around 20 to 30 F, lows around 0 to 10 F, typical winter day in Iowa.
Very cold: Highs around 0 to 10 F, lows sub 0 F (like -10 or -20 F)...