Most of Nebraska is gently rolling prairie, although the river valleys, much of south-central Nebraska, and a large portion of the panhandle district are flatlands. The central part of the state is part of the Great Plains. The eastern part of the state lies on the till plains of the Central Lowland. The Sand Hills of the north-central plain is an unusual region of sand dunes anchored by grasses that cover about 18,000 sq mi (47,000 sq km) and contains many small lakes and luxuriant grasses. The land in Nebraska slopes gradually upward from east to west, from a low of 840 ft (256 m) in the southeast to 5,424 ft (1,654 m) high in Kimball County.
Nebraska lies within the Missouri River drainage system; the Platte, the major Nebraska tributary, joins the Missouri south of Omaha. Although shallow and unnavigable, the Platte provides important irrigation. The Republican and Big Blue rivers flow through southern Nebraska, emptying into the Missouri in Kansas. The Niobrara, a swift-moving stream that rises in the high country just west of the Wyoming border, flows across the far north of the state. The Ogallala Aquifer is a huge supply of underground water that lies beneath most of Nebraska. The aquifer makes well irrigation possible in much of the state. The Sand Hills region is dotted with small natural lakes, but in the rest of the state, the main lakes are artificial.
As is much of the Great Plains area, Nebraska’s climate has extremes in temperature, wind speeds, and precipitation. In general, Nebraska has a continental climate. There are also big differences in the climate between eastern Nebraska and the central and westernmost regions. Hot winds from the southwest often push summer temperatures in Nebraska into the 90s F (about 32°C) and sometimes above 100°F (38°C).
Average July temperatures range from the mid-70s F (about 23°C) in the panhandle to the upper 70s F (about 26°C) in the southeast. In the winter, northwestern winds often bring in Arctic air from Canada, and temperatures are often far below 0 °F (about -18°C). The record low for the state is -47°F (-44°C), registered in Morrill County on 12 February 1899; the record high of 118°F (48°C) was recorded at Minden on 24 July 1936.
The average annual precipitation varies from more than 30in (750mm) in the southeast to less than 16in (400mm) in the extreme west. Blizzards, droughts, and windstorms have plagued Nebraskans throughout their history.
