The general climate is temperate, with notable exceptions. Alaska has an arctic tundra, while Hawaii, South Florida, Puerto Rico and the U.S. Virgin Islands are tropical. The Great Plains are dry, flat and grassy, merging into arid desert in the far west and the Mediterranean on the California coast.
In winter, the major cities in the north and mid-west of the country can get up to 61 cm of snow in one day, with cold temperatures. Summers are humid but mild. Temperatures sometimes exceed 100°F (38°C) in the Midwest and Great Plains. Some areas of the northern plains can experience cold temperatures of -34°C (-30°F) in winter. Temperatures below -18°C (0°F) sometimes reach southern Oklahoma.
The climate in the south also varies. In summer it is hot and humid, but from October to April the weather can range from 15°C (60°F) to short cold spells of -7°C (20°F).
In the Great Plains and Midwestern states, tornadoes also occur from late spring to early autumn, earlier in the south and later in the north. States along the Atlantic and Gulf coasts can experience hurricanes between June and November. These intense and dangerous storms often avoid the continental United States, but evacuations are often ordered and should be considered.
The Rocky Mountains are cold and snowy. Some parts of the Rocky Mountains receive more than 1,200 cm of snow in a season. Even in summer, temperatures in the mountains are cool and snow can fall almost all year round. Unprepared climbing in the mountains in winter is dangerous and the roads through the mountains can be very icy.
The southwestern deserts are hot and dry in summer, with temperatures often exceeding 100°F (38°C). From July to September, frequent thunderstorms can be expected in the southwest. Winters are mild, and snow is uncommon. Average annual precipitation is low, usually less than 25 cm (10 in).
In the coastal Northwest (Oregon and Washington west of the Cascade Range and the northern part of California west of the Coastal/Cascade Range), cool, wet weather is common most of the year. Summers (July to September) are usually quite dry with low humidity, making it an ideal climate for outdoor activities. In winter, rain is more frequent, snow is rare, especially on the coast, and temperature extremes are rare. Rain falls almost exclusively from late autumn to early spring on the coast. East of the Cascades, the northwest is much drier. Much of the interior of the Northwest is semi-arid to desert, especially in Oregon.
Cities in the northeast and upper south are known for summers with temperatures of 90°C (32°C) or higher, with extremely high humidity, usually above 80%. This can be a dramatic change from the southwest. The high humidity means that the temperature can feel warmer than the actual readings. The northeast also experiences snow, and there is a large snowfall at least once every two years.