Pakistan is divided into five distinct geographic regions: The Thar Desert and Lower Indus Valley in the south with arid valleys and rocky hills; The Baluchistan Plateau toward the west with elevation between 1,000 and 3,000 feet (300-900 meters) and covering nearly half the nation's territory; The Indus Basin, an irrigated agricultural area in the northeast; The Northwest Frontier, an area of barren mountains and irrigated valleys bordering Afghanistan; and The Far North with snowcapped mountains reaching high elevations. Seasonal temperatures vary widely in these five regions. With the exception of the Far North, summers are hot throughout the country with temperatures ranging to 90-120°F (32-49°C) and little nighttime relief. Trade winds provide some relief during the hot and humid summers in Karachi and a brief cool season comes between December and February. In Lahore, Islamabad, and Peshawar a distinct winter season brings daytime temperatures of 60°F (16°C) or less, cold nights, and - in Islamabad and Peshawar - frequent morning frost does occur during the stark winter season. Altitude governs climate in the Far North, with pleasant summers in the lower regions and perpetual snow in the higher mountains. The average annual rainfall varies from 6 inches (40 cm) in Karachi, 15 (38 cm) in Peshawar, 18 (46 cm) in Lahore, to about 30 (76 cm) in Islamabad. Most rain falls during the summer monsoon from July to September, although parts of the Northwest Frontier and the Indus Basin experience a moderate winter rainy season as well.