The humid subtropical climate (Koppen Cfa) of central, southern and eastern Oklahoma is influenced heavily by southerly winds bringing moisture from the Gulf of Mexico. Traveling westward, the climate transitions progressively toward a semi-arid zone (Koppen BSk) in the high plains of the Panhandle and other western areas from about Lawton westward, less frequently touched by southern moisture. Precipitation and temperatures decline from east to west accordingly, with areas in the southeast averaging an annual temperature of 62 °F (17 °C) and an annual rainfall of generally over 40 inches (1,020 mm) and up to 56 inches (1,420 mm), while areas of the (higher-elevation) panhandle average 58 °F (14 °C), with an annual rainfall under 17 inches (430 mm).