The climate is mostly temperate, with some amazing exceptions. Alaska is an arctic state, while Hawaii, essentially in the middle of the Pacific ocean, and Florida are tropical. The western half of the country is covered by plains and mountains. The Great Plains are dry, flat and grassy turning further west into arid desert with startling outcrops of rock columns and deep canyons. As with all places, anyone planning to visit a place in the US should familiarize themselves with the local climatology and pack clothes or items as appropriate. Seasons vary dramatically in some locations in the US, including the northern and mid-western major cities. During the winter, Northern cities such as New York, Chicago, or Boston see a great deal of snow (in some cases as much as two feet (61 cm) or more during a single snowstorm) and can experience bitterly cold temperatures. Summers, however, are usually mild and on some days very humid. However, temperatures over 100°F (38°C) sometimes invade the entire Midwest and Great Plains region. Some areas in the northern plains can experience dangerously cold temperatures of -30°F (-34°Celsius) during the winter. Temperatures below 0°F (-18°C) sometimes invade as far south as Kansas or even Oklahoma.

The Great Plains & Midwestern states also experience tornadoes from the late spring to the early fall. Tornado season generally runs from Spring-early Summer in the south to Summer-early Fall in the north. If you plan to visit an area in these parts of the country you might want to visit the Tornado Safety page, be sure to stay alert to the weather forecast and to keep an eye on the sky for ominous clouds. Many areas also have warning sirens which will sound, indicating a tornado is nearby and cover should be sought. The climate of the Southeastern states is characterized by the phrase, "the long, hot, summer" - sticky too, one might add. Humidity and high temperatures make warmer months in these states good for little but sipping iced tea and plunging oneself into cool bodies of water. Winter is another matter entirely. Bright, clear, warmer-than-average days make outdoor activities possible nearly every winter day. Autumn is balmy and exhilarating, when color flows down from the mountains to the sea. A visit to the Southeast is best undertaken from October through April, when weather is glorious, and chiggers (a small insect which burrows into human flesh) and skeeters are subsiding. The Southeastern states, especially along the Atlantic coast and the Gulf of Mexico, may experience hurricanes. These monster storms are quite common during the summer, but few actually strike the U.S. mainland. If, however, one is forecast, do not take the situation lightly. Evacuations are often ordered for areas in the path of the storm and should be heeded.

The Rockies are very cold and snowy, with some regions seeing over 500 inches (1,200 cm) of snow in a season. Some of the world's most famous ski resorts are located in Colorado and Utah. Even during the summer temperatures are cool in the mountains, and snow can fall nearly year-round. In the Intermountain West, (which consists of the Great Basin and several plateaus and basins extending through eastern Oregon and Washington), temperatures often drop below 0°F (-18°C) during winter and above 100°F (38°C) during summer. Snow is common during winter and precipitation scarce, averaging less than 15 inches (38 cm) annually across almost the entire region. The Southwestern deserts are extremely arid and hot during the summer, with summer temperatures exceeding 100°F (38°C) through most of the summer. This includes such cities as Las Vegas and Phoenix. Thunderstorms can be expected in the southwest frequently from July through September due to the summer monsoon that rises from Mexico. Winters in this region are mild, and snow is unusual. Average annual precipitation is less than 10 inches (25 cm). Cool and damp weather is common in the northwest in areas such as in Seattle or Portland. Rain is most frequent in winter, and snow is rare along the coastal regions. The Pacific coast is rainy and cool. The Pacific coast rarely sees snow and extremes in temperature are uncommon. Rain falls almost exclusively from late fall through early spring along the coast, except in Washington, where rain falls year-round.

The Missouri-Mississippi river system runs from the far north to the Gulf of Mexico, cutting the country almost in half, and giving a convenient mental border between "East" and "West." These rivers sometimes flood.