Originally, h signified low-latitude climate (average annual temperature above 18 °C) while k signified middle-latitude climate (average annual temperature below 18 °C), but the more common practice today, especially in the United States, is to use h to mean the coldest month has an average temperature above 0 °C (32 °F) (or -3.0 °C ), with k denoting that at least one month averages below 0 °C.