what time zones are there in the us?
North American Eastern Time Zone UTC−06:00 Mountain Time Zone Hawaii–Aleutian Time Zone Pacific Time Zone Samoa Time Zone Alaska Time Zone UTC-5 Atlantic Time Zone Central Time Zone
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 In the USA , The Smithsonian Institution developed its network of observers over much of the central and eastern United States between the 1840s and 1860s once Joseph Henry took the helm . The U.S. Army Signal Corps inherited this network between 1870 and 1874 by an act of Congress , and expanded it to the west coast soon afterwards . At first , not all the data on the map was used due to a lack of time standardization . The United States fully adopted time zones in 1905 , when Detroit finally established standard time . 

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 Start and end dates vary with location and year . Since 1996 , European Summer Time has been observed from the last Sunday in March to the last Sunday in October ; previously the rules were not uniform across the European Union . Starting in 2007 , most of the United States and Canada observe DST from the second Sunday in March to the first Sunday in November , almost two @-@ thirds of the year . The 2007 US change was part of the Energy Policy Act of 2005 ; previously , from 1987 through 2006 , the start and end dates were the first Sunday in April and the last Sunday in October , and Congress retains the right to go back to the previous dates now that an energy @-@ consumption study has been done . Proponents for permanently retaining November as the month for ending DST point to Halloween as a reason to delay the change — to provide extra daylight on October 31 . 

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 The United States , with its large size and geographic variety , includes most climate types . To the east of the 100th meridian , the climate ranges from humid continental in the north to humid subtropical in the south . The Great Plains west of the 100th meridian are semi @-@ arid . Much of the Western mountains have an alpine climate . The climate is arid in the Great Basin , desert in the Southwest , Mediterranean in coastal California , and oceanic in coastal Oregon and Washington and southern Alaska . Most of Alaska is subarctic or polar . Hawaii and the southern tip of Florida are tropical , as are the populated territories in the Caribbean and the Pacific . Extreme weather is not uncommon — the states bordering the Gulf of Mexico are prone to hurricanes , and most of the world 's tornadoes occur within the country , mainly in Tornado Alley areas in the Midwest and South . 

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