🇺🇸United States

The United States (9,834,000 km²) spans 25°–71°N, 65°–172°W across seven distinct climate zones from Arctic tundra to tropical, forming one of Earth's most climatically diverse nations with extraordinary variation governed by latitude, continental position, mountain barriers, and ocean currents.

The continental climate (Köppen Dfa/Dfb) dominates the interior and Northeast with warm-to-hot summers (July averages 18–28°C) and cold winters (January −12 to 0°C), transitioning westward into semi-arid steppes (BSk) across the Great Plains where precipitation drops from 1,000 mm east of the Mississippi to 400 mm at the Rockies' rain shadow.

The humid subtropical Southeast (Cfa) experiences hot, humid summers exceeding 27°C and mild winters with 1,000–1,500 mm annual rainfall concentrated in summer thunderstorms and tropical systems. The Southwest deserts (BWh/BWk) receive under 250 mm precipitation annually with extreme summer heat surpassing 45°C in Death Valley.

The Pacific Northwest (Csb/Cfb) features mild, wet winters and dry summers with orographic precipitation exceeding 3,000 mm in the Cascades and Olympic Mountains, while California exhibits Mediterranean climate (Csa/Csb) with winter rainfall maxima. Alaska encompasses Arctic tundra (ET), subarctic (Dfc), and maritime zones, while Hawaii displays tropical conditions. The Rocky Mountains create profound rain-shadow effects and altitudinal climate gradients from montane forests to alpine tundra above 3,500 m.

The region experiences record-breaking extreme weather events. Major hurricanes include Ian (2022, $113 billion in damages), Helene (September 2024, severe flooding across the Southeast and southern Appalachians), and Harvey (August 2017, over 1,500 mm rainfall in four days, 88 deaths). Notable heat records include the 2021 Pacific Northwest heat dome (Portland 46.7°C, Seattle 42.2°C) and the August 2023 Maui Lahaina wildfire (over 100 deaths).

The 2024 Smokehouse Creek Fire in the Texas Panhandle burned over 1 million acres. The August 2020 derecho crossed 1,200 km across Iowa and Illinois with winds exceeding 190 km/h and $11 billion in crop damage. Sea-level rise drives increased nuisance flooding in Miami, Norfolk, and Charleston.

Our archive covers 355 US cities with daily ERA5 reanalysis data going back to 1940. The warmest July averages occur in Phoenix, around 41.6°C, while Fargo records the coldest January nights near −17.4°C. Comparing the last decade against the 1940–1970 baseline, mean temperatures across these cities have risen by about 1.6°C.