The contiguous United States or "Lower 48" (the 48 states other than Alaska and Hawaii) are bounded by the Atlantic Ocean to the east and the Pacific Ocean to the west, with much of the population living on these two coasts. Its only land borders are shared with Canada to the north, and Mexico to the south. The U.S. also shares maritime borders with Russia, Cuba, and the Bahamas.
The country has three major mountain ranges. The Appalachians extend from Canada to the state of Alabama, a few hundred miles west of the Atlantic Ocean. They are the oldest of the three mountain ranges and offer spectacular sightseeing and excellent camping spots. The Rockies are, on average, the highest in North America, extending from Alaska to New Mexico, with many areas protected as national parks. They offer hiking, camping, skiing, and sightseeing opportunities. The combined Sierra Nevada and Cascade ranges are the youngest. The Sierras extend across the "backbone" of California, with sites such as Lake Tahoe and Yosemite National Park, then give way to the even younger volcanic Cascade range, with some of the highest points in the country.
The Great Lakes define much of the border between the eastern United States and Canada. More inland seas than lakes, they were formed by the pressure of glaciers retreating north at the end of the last Ice Age. The five lakes span hundreds of miles, bordering the states of Minnesota, Wisconsin, Illinois, Indiana, Michigan, Ohio, Pennsylvania and New York, and their shores vary from pristine wilderness areas to industrial "rust belt" cities. They are the second-largest bodies of freshwater in the world, after the polar ice caps.
The overall climate is temperate, with notable exceptions. Alaska has Arctic tundra, while Hawaii and South Florida are tropical. The Great Plains are dry, flat and grassy, turning into arid desert in the far West and Mediterranean along the California coast.
In the winter, the northern and mid-western major cities can see as much as 2 feet (61 cm) of snowfall in one day, with cold temperatures. Summers are humid, but mild. Temperatures over 100°F (38°C) sometimes invade the Midwest and Great Plains. Some areas in the northern plains can experience cold temperatures of -30°F (-34°C) during the winter. Temperatures below 0°F (-18°C) sometimes reach as far south as Oklahoma.
The climate of the South also varies. In the summer, it is hot and humid, but from October through April the weather can range from 60°F (15°C) to short cold spells of 20°F (-7°C) or so.
The Great Plains & Midwestern states also experience tornadoes from the late spring to early fall, earlier in the south and later in the north. States along the Atlantic coast and the Gulf of Mexico, may experience hurricanes between June and November. These intense and dangerous storms frequently miss the the U.S. mainland, but evacuations are often ordered and should be heeded.
The Rockies are cold and snowy. Some parts of the Rockies see over 500 inches (1,200 cm) of snow in a season. Even during the summer, temperatures are cool in the mountains, and snow can fall nearly year-round. It is dangerous to go up in the mountains unprepared in the winter and the roads through them can get very icy.
The deserts of the Southwest are hot and dry during the summer, with temperatures often exceeding 100°F (38°C). Thunderstorms can be expected in the southwest frequently from July through September. Winters are mild, and snow is unusual. Average annual precipitation is low, usually less than 10 inches (25 cm).
Cool and damp weather is common in the northwest (the states of Oregon, Washington and the northern part of California). Rain is most frequent in winter, snow is rare, especially along the coast and extreme temperatures are uncommon. Rain falls almost exclusively from late fall through early spring along the coast.
Northeastern and cities of the Upper South are known for summers with temperatures reaching into the 90's (32 C) or more, with extremely high humidity, usually over 80%. This can be a drastic change from the Southwest. High humidity means that the temperature can feel hotter than actual readings. The Northeast also experiences snow, and at least once every few years there will be a dumping of the white stuff in enormous numbers.