The United States spans at least six major climate regions, ranging from tropical rainforest in Hawaii to arctic tundra in northern Alaska. That diversity exists because the country covers roughly 25 degrees of latitude across the mainland alone, with mountain ranges, ocean currents, and the Gulf of Mexico each pulling regional weather in different directions. Understanding these regions helps explain why rainfall, temperature swings, and growing seasons vary so dramatically from one part of the country to another.
Humid Continental: The Northeast and Upper Midwest
The Northeast and Upper Midwest share a humid continental climate defined by sharp seasonal contrasts. Summer averages sit around 65°F, winter averages drop to about 35°F, and the gap between the two creates the classic four-season cycle. In the northern reaches of this zone, January mean temperatures can fall well below 0°F during outbreaks of polar air, while July highs regularly climb into the low 80s.
This region gets reliable precipitation year-round, typically 35 to 50 inches annually, spread fairly evenly across the seasons. Snow is a major feature from late November through March, especially in lake-effect belts near the Great Lakes. The Midwest portion of this zone is especially prone to clashing air masses: extremely cold air from Canada collides with warm, humid air from the Gulf of Mexico, producing severe thunderstorms, tornadoes, and heavy downpours that have grown more intense in recent decades. Major heat waves have also become more frequent across the Midwest, and nighttime and winter temperatures have risen faster than daytime highs.
Humid Subtropical: The Southeast
From Virginia and the Carolinas south through Georgia, Alabama, Mississippi, and into eastern Texas, the climate shifts to humid subtropical. The defining trait is moisture: high humidity for much of the year, summer temperatures that regularly hit 90°F or higher, and winters that stay above freezing on average. Winter cold snaps do happen when polar air pushes south, briefly dropping temperatures into the single digits on the northern edge, but those episodes are short-lived compared to what the Northeast experiences.
Annual rainfall is generous, often 45 to 60 inches, with summer afternoon thunderstorms contributing a large share. The Southeast also sits in the path of Atlantic hurricanes from June through November, which can dump enormous amounts of rain in a short period. This combination of heat, humidity, and precipitation supports the lush vegetation the region is known for, from the pine forests of the Piedmont to the cypress swamps of Louisiana.
The Great Plains: A Gradient From Wet to Dry
The Great Plains stretch from Texas north through Oklahoma, Kansas, Nebraska, and the Dakotas, and the most important climate feature here is a dramatic east-to-west rainfall gradient. Eastern Texas and Oklahoma receive more than 50 inches of rain per year, while parts of Montana, Wyoming, and western Texas get less than 15 inches. The rough dividing line falls near the 100th meridian, a north-south line running through the Dakotas, Nebraska, and central Texas. East of it, the landscape is green enough for rain-fed farming. West of it, the land turns semi-arid, and agriculture depends heavily on irrigation.
Temperature extremes are a hallmark. Without mountains or large bodies of water to moderate conditions, the Plains experience some of the widest temperature swings in the country. Summer highs above 100°F and winter lows well below zero are both common in the same locations. In 2024, portions of the Dakotas recorded temperatures more than 4°F above their recent 30-year normal, making it one of the warmest years on record for the northern Plains.
Arid and Semi-Arid: The Southwest
The Southwest, including Arizona, Nevada, Utah, New Mexico, and parts of western Texas, is the driest part of the country. Much of this region qualifies as true desert, with annual rainfall in some areas below 10 inches and summer temperatures that routinely exceed 110°F in low-elevation valleys. Humidity is minimal for most of the year, which makes the dry heat more tolerable than equivalent temperatures in the Southeast but also accelerates water loss from soils and reservoirs.
The notable exception to the year-round dryness is the North American Monsoon, a seasonal pattern that brings bursts of moisture from the Gulf of California into Arizona and New Mexico from roughly July through September. These monsoon thunderstorms can be intense but localized, dropping heavy rain on one canyon while leaving the next one bone dry. Between 2000 and 2015, every part of the Southwest experienced higher average temperatures than the long-term historical average, with some areas nearly 2°F warmer. In a region where water is already scarce, even small temperature increases drive more evaporation and put serious pressure on water supplies.
Marine West Coast: The Pacific Northwest
Western Washington and Oregon, from the coast inland to the Cascade Range, have a marine west coast climate shaped almost entirely by the Pacific Ocean. Cold water flowing south from the Gulf of Alaska keeps coastal air temperatures cool and remarkably stable. Summer highs in Seattle and Portland typically reach the mid-70s, while winter lows rarely drop below the mid-30s. The annual temperature swing is among the smallest in the mainland U.S.
What the region is best known for is rain, or more precisely, persistent cloudiness and drizzle from October through May. Seattle averages around 150 rainy days per year, though its actual rainfall total (about 37 inches) is less than many Eastern cities. The rain comes gently and frequently rather than in heavy bursts. The Cascade Range creates a sharp rain shadow: western slopes catch enormous amounts of moisture, while cities just east of the mountains, like Yakima, receive as little as 8 inches annually.
Mediterranean: Coastal California
California’s coast has a Mediterranean climate, one of only a handful of places in the world where nearly all precipitation falls in winter and summers are almost completely dry. This reversed wet-dry cycle sets it apart from most of the U.S., where summer thunderstorms contribute a significant share of annual rainfall. Along the central and northern coast, summers are further cooled by fog that rolls in from the cold Pacific, keeping temperatures in the 60s even in July and August. Southern California’s coast is warmer and sunnier but follows the same basic pattern of wet winters and dry summers.
Inland California is a different story. The Central Valley, blocked from ocean moisture by coastal mountains, receives as little as 6 to 7 inches of rain per year in places like Bakersfield and functions essentially as a desert that has been transformed into farmland through massive irrigation systems.
Alaska’s Polar and Subarctic Zones
Alaska alone contains more climate diversity than most countries. The northern coast along the Arctic Ocean is true tundra, where permafrost underlies the ground year-round, winter temperatures drop below minus 40°F, and the growing season lasts only a few weeks. The Brooks Range separates this tundra from the vast interior, which falls into the subarctic zone: long, bitterly cold winters and short summers where temperatures can briefly spike into the 80s or even 90s.
Southern and southeastern Alaska, including Juneau and the Aleutian Islands, have a much milder oceanic climate. Coastal towns benefit from the moderating influence of the Pacific and see heavy rainfall (Juneau averages over 60 inches per year) but relatively mild winters for their latitude. The Aleutian chain is characterized by oceanic meadow and heath landscapes, with near-constant wind and cloud cover.
Hawaii’s Tropical Climate
Hawaii is the only U.S. state with a tropical rainforest climate. Temperatures hover between 70°F and 85°F year-round at sea level, with minimal seasonal variation. Rainfall, however, varies wildly over short distances because of the islands’ mountainous terrain. Windward slopes facing the northeast trade winds are among the wettest places on Earth. Mount Waialeale on Kauai averages roughly 450 inches of rain per year. Leeward sides of the same islands can be dry and sunny, receiving under 20 inches annually.
A Warming Baseline Across All Regions
These climate regions still hold their essential character, but temperatures are shifting. In 2024, the contiguous U.S. recorded an average annual temperature of 55.5°F, which was 3.5°F above the 20th-century average and the warmest year in the 130-year record. The Northeast hit its hottest year ever at 50.5°F, a full 2.8°F above normal. The Midwest was 3.2°F above its recent baseline. Every state in the South ranked among its three warmest years on record, and most of the West ran 1 to 3°F above normal.
These shifts don’t erase the boundaries between climate regions, but they do push them. Growing seasons are lengthening in the North, drought pressure is intensifying in the Southwest, and heavy rainfall events are becoming more common in the Midwest and Southeast. The USDA’s Plant Hardiness Zone Map, which gardeners and farmers use to determine which plants can survive local winters, is based on average extreme minimum temperatures and has been updated to reflect these changes. Zones that once applied to a given location may no longer match what actually grows there.