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132-487: The Weather Prediction Center issues storm summaries on storm systems bringing significant rainfall and snowfall to portions of the United States . They also forecast precipitation amounts for the lower 48 United States for systems expected to impact the country over the next seven days. Advisories are also issued for tropical cyclones which have moved inland, weakened to tropical depression strength, and are no longer

264-580: A " Special Relationship " with the United Kingdom and strong ties with Canada , Australia , New Zealand , the Philippines , Japan , South Korea , Israel , and several European Union countries ( France , Italy , Germany , Spain , and Poland ). The U.S. works closely with its NATO allies on military and national security issues, and with countries in the Americas through

396-457: A 24-hour period. These products are issued in probabilistic form to better represent the forecast uncertainty associated with a particular event. The Winter Weather Desk produces a heavy snow and icing discussion that provides the meteorological reasoning for the 24-hour probabilistic heavy snow and icing guidance graphics. This text message is used by internal and external clients including NWS field offices, Department of Homeland Security , FEMA ,

528-679: A 5 km (3.1 mi) horizontal resolution. The purpose of the WPC Model Diagnostic Discussion is to provide objective information and subjective interpretation concerning the current runs of the NCEP short range numerical models. The WPC model diagnostic meteorologist prepares the Model Diagnostic Discussion twice per day in two parts, corresponding to the 0000 UTC and 1200 UTC model runs. This narrative consists of three sections: an evaluation of

660-841: A collaborative effort with the Ocean Prediction Center , the National Hurricane Center , and the Honolulu Weather Forecast Office. The WPC focuses on the synoptic and mesoscale features over North America, primarily north of 31N. The surface analysis is a manual analysis of surface fronts and pressure over North America and adjacent oceans performed every three hours. The analysis utilizes a variety of weather data in addition to observations of surface weather conditions, such as upper air observations, global satellite imagery, Doppler weather radar, and model mass fields to ensure that

792-405: A consensus of forecast models, as well as ensemble members of the various models, can help reduce forecast error. However, regardless how small the average error becomes with any individual system, large errors within any particularly piece of guidance are still possible on any given model run. Professionals are required to interpret the model data into weather forecasts that are understandable to

924-542: A coordinated, continent-wide military effort. Finally, deteriorating relations between the British military establishment and the colonists, relations that were already less than positive, set the stage for further distrust and dislike of British troops. Following their victory in the French and Indian War, Britain began to assert greater control over local colonial affairs, resulting in colonial political resistance ; one of

1056-534: A decentralized government that operated until 1789. After the British surrender at the siege of Yorktown in 1781 American sovereignty was internationally recognized by the Treaty of Paris (1783), through which the U.S. gained territory stretching west to the Mississippi River, north to present-day Canada, and south to Spanish Florida . The Northwest Ordinance (1787) established the precedent by which

1188-414: A depiction of the types and extent of precipitation that are forecast at the valid time of the chart. In addition, discussions are written on each shift and issued with the forecast packages that highlight the meteorological reasoning behind the forecasts and significant weather across the continental United States. Medium range forecasters are responsible for preparing forecasts for three to seven days into

1320-753: A federal capital district, Washington, D.C. The 48 contiguous states border Canada to the north and Mexico to the south, with the states of Alaska to the northwest and the archipelagic Hawaii in the Pacific Ocean . The United States also asserts sovereignty over five major island territories and various uninhabited islands . The country has the world's third-largest land area , largest exclusive economic zone , and third-largest population , exceeding 334 million. Its three largest metropolitan areas are New York , Los Angeles , and Chicago , and its three most populous states are California , Texas , and Florida . Paleo-Indians migrated across

1452-407: A few prominent industrialists , largely by their formation of trusts and monopolies to prevent competition. Tycoons led the nation's expansion in the railroad , petroleum , and steel industries. The United States emerged as a pioneer of the automotive industry . These changes were accompanied by significant increases in economic inequality , slum conditions , and social unrest , creating

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1584-424: A forecast increases with time as errors decrease. There comes a point when the errors are so large that the forecast has no correlation with the actual state of the atmosphere. Looking at a single forecast model does not indicate how likely that forecast is to be correct. Ensemble forecasting entails the production of many forecasts to reflect the uncertainty in the initial state of the atmosphere (due to errors in

1716-666: A global reach. The U.S. is a founding member of the World Bank , Organization of American States , NATO , and the United Nations , as well as a permanent member of the UN Security Council . The first documented use of the phrase "United States of America" is a letter from January 2, 1776. Stephen Moylan , a Continental Army aide to General George Washington , wrote to Joseph Reed , Washington's aide-de-camp , seeking to go "with full and ample powers from

1848-419: A matter of hours. Radar imagery forecasting techniques show higher skill than model forecasts within 6 to 7 hours of the time of the radar image. In the past, the forecaster was responsible for generating the entire weather forecast based upon available observations. Today, meteorologists' input is generally confined to choosing a model based on various parameters, such as model biases and performance. Using

1980-485: A narrative is issued for each set of forecasts highlighting forecast reasoning and significant weather over the Continental United States. Separate forecasts, similar to the 5-day mean products, are prepared for Hawaii. The Alaska medium range forecasters review the latest deterministic and ensemble model guidance (similar to how the broader medium range forecasts are created) in an effort to compose

2112-802: A number of other national centers such as the Climate Prediction Center (CPC), Environmental Modeling Center (EMC), National Hurricane Center (NHC), Ocean Prediction Center (OPC), Storm Prediction Center (SPC), Aviation Weather Center (AWC), NCEP Central Operations, and the Space Weather Prediction Center (SWPC). During August 2012, HPC moved to a new building, the National Center for Weather and Climate Prediction (NCWCP), in College Park, Maryland . On March 5, 2013, HPC changed its name to

2244-598: A period of heightened, overt racism following Reconstruction, a time often called the nadir of American race relations . A series of Supreme Court decisions, including Plessy v. Ferguson , emptied the Fourteenth and Fifteenth Amendments of their force, allowing Jim Crow laws in the South to remain unchecked, sundown towns in the Midwest, and segregation in communities across the country , which would be reinforced by

2376-488: A prominent leader in the early 1960s. The Great Society plan of President Lyndon Johnson 's administration resulted in groundbreaking and broad-reaching laws, policies and a constitutional amendment to counteract some of the worst effects of lingering institutional racism . The counterculture movement in the U.S. brought significant social changes, including the liberalization of attitudes toward recreational drug use and sexuality . It also encouraged open defiance of

2508-526: A sense of manifest destiny . The Missouri Compromise attempted to balance the desire of northern states to prevent the expansion of slavery into new territories with that of southern states to extend it, admitting Missouri as a slave state and Maine as a free state. It further prohibited slavery in all other lands of the Louisiana Purchase north of the 36°30′ parallel . As Americans expanded further into land inhabited by Native Americans,

2640-614: A sense of American identity as well. Men who otherwise never left their own colony now traveled across the continent to fight alongside men from decidedly different backgrounds but who were no less "American". British officers trained American officers for battle, most notably George Washington ; these officers would lend their skills and expertise to the colonists' cause during the American Revolutionary War to come. In addition, colonial legislatures and officials found it necessary to cooperate intensively in pursuit of

2772-498: A specified time period over a specified area. A QPF will be created when precipitation amounts reaching a minimum threshold are expected during the forecast's valid period. Valid periods of precipitation forecasts are normally synoptic hours such as 00:00, 06:00, 12:00 and 18:00  GMT . Terrain is considered in QPFs by use of topography or based upon climatological precipitation patterns from observations with fine detail. Starting in

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2904-400: A tropical cyclone, yet the system is still capable of producing flooding type rains. This WPC Public Advisory will continue to be issued until the flooding rainfall threat is over. The advisory will contain information on how much rainfall has occurred with a particular tropical system, and will also include forecast information on the remnants of the system. This responsibility has been held by

3036-526: A variety of responsibilities, primarily the training of foreign visitors in the use of Numerical Weather Prediction products. The International desk routinely hosts visitors from Central and South America and the Caribbean. Visiting meteorologists train, and also generate forecasts for their own national centers, and assist WPC forecasters with QPF related to tropical cyclones in Central America and

3168-464: A year). Juvenile correctional facilities are operated by local or state governments and serve as longer-term placements for any minor adjudicated as delinquent and ordered by a judge to be confined. As of January 2023, the United States has the sixth-highest per capita incarceration rate in the world—531 people per 100,000 inhabitants—and the largest prison and jail population in

3300-467: Is a forecast of expected rainfall amounts that will occur with the tropical cyclone. Finally, the WPC surface analysis desk has the responsibility for issuing Public Advisories whenever a tropical cyclone has made landfall in the U.S. or adjacent parts of Mexico, has weakened below tropical storm status (i.e. to a tropical depression or post-tropical cyclone or low) and is not expected to re-emerge over water as

3432-591: Is believed to be the first widespread culture in the Americas. Over time, indigenous North American cultures grew increasingly sophisticated, and some, such as the Mississippian culture , developed agriculture , architecture , and complex societies . In the post-archaic period , the Mississippian cultures were located in the midwestern , eastern , and southern regions, and the Algonquian in

3564-597: Is expected. The red warning indicates rainfall amounts of 50 millimetres (2.0 in) per hour are anticipated. The black warning indicates that rainfall rates of 70 millimetres (2.8 in) are possible. Within the United States, the Hydrometeorological Prediction Center , River Forecast Centers, and local forecast offices within the National Weather Service create precipitation forecasts for up to five days in

3696-415: Is known as probability of precipitation . These probabilities can be derived from a deterministic forecast using computer post-processing. The Bureau of Meteorology began a method of forecasting rainfall using a combination, or ensemble, of different forecast models in 2006. It is termed The Poor Man's Ensemble (PME). Its forecasts are more accurate over time than any of the individual models composing

3828-498: Is known as the presidential system , in contrast to the parliamentary system , where the executive is part of the legislative body. Many countries around the world imitated this aspect of the 1789 Constitution of the United States , especially in the Americas. The Constitution is silent on political parties. However, they developed independently in the 18th century with the Federalist and Anti-Federalist parties. Since then,

3960-438: Is now the United States experienced conflicts with Native Americans, they also engaged in trade, exchanging European tools for food and animal pelts. Relations ranged from close cooperation to warfare and massacres. The colonial authorities often pursued policies that forced Native Americans to adopt European lifestyles, including conversion to Christianity. Along the eastern seaboard, settlers trafficked African slaves through

4092-552: Is the federal agency charged with addressing most environmental-related issues . The idea of wilderness has shaped the management of public lands since 1964, with the Wilderness Act . The Endangered Species Act of 1973 provides a way to protect threatened and endangered species and their habitats. The United States Fish and Wildlife Service implements and enforces the Act. In 2024, the U.S. ranked 34th among 180 countries in

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4224-603: The Allies of World War I , helping to turn the tide against the Central Powers . In 1920, a constitutional amendment granted nationwide women's suffrage . During the 1920s and '30s, radio for mass communication and the invention of early television transformed communications nationwide. The Wall Street Crash of 1929 triggered the Great Depression , which President Franklin D. Roosevelt responded to with

4356-553: The Atlantic slave trade . The original Thirteen Colonies that would later found the United States were administered as possessions of Great Britain , and had local governments with elections open to most white male property owners . The colonial population grew rapidly, eclipsing Native American populations; by the 1770s, the natural increase of the population was such that only a small minority of Americans had been born overseas. The colonies' distance from Britain allowed for

4488-817: The Bering land bridge more than 12,000 years ago, and formed various civilizations and societies . British colonization led to the first settlement of the Thirteen Colonies in Virginia in 1607. Clashes with the British Crown over taxation and political representation sparked the American Revolution , with the Second Continental Congress formally declaring independence on July 4, 1776. Following its victory in

4620-549: The Environmental Performance Index . The country joined the Paris Agreement on climate change in 2016 and has many other environmental commitments. The United States is a federal republic of 50 states and a separate federal capital district, Washington, D.C. It also asserts sovereignty over five unincorporated territories and several uninhabited island possessions . The U.S. is

4752-644: The European Centre for Medium-Range Weather Forecasts (ECMWF), the United Kingdom's Met Office (UKMET), the Meteorological Service of Canada, including ensembles. Coordination with the surface analysis, model diagnostics, quantitative precipitation, winter weather, and tropical forecast desks is performed during the short range forecast process to maintain internal consistency. The short range forecast products include surface pressure patterns, circulation centers and fronts for 6–60 hours, and

4884-500: The Federal Bureau of Investigation (FBI) and the U.S. Marshals Service have national jurisdiction and specialized duties, such as protecting civil rights , national security and enforcing U.S. federal courts ' rulings and federal laws. State courts conduct most civil and criminal trials, and federal courts handle designated crimes and appeals of state court decisions . There is no unified "criminal justice system" in

5016-720: The Great Lakes , Mississippi River and Gulf of Mexico . British colonization of the East Coast began with the Virginia Colony (1607) and Plymouth Colony (1620). The Mayflower Compact and the Fundamental Orders of Connecticut established precedents for representative self-governance and constitutionalism that would develop throughout the American colonies. While European settlers in what

5148-719: The Great Lakes region and along the Eastern Seaboard , while the Hohokam culture and Ancestral Puebloans inhabited the southwest . Native population estimates of what is now the United States before the arrival of European immigrants range from around 500,000 to nearly 10 million. Christopher Columbus began exploring the Caribbean for Spain in 1492, leading to Spanish-speaking settlements and missions from Puerto Rico and Florida to New Mexico and California . France established its own settlements along

5280-524: The House of Representatives , a lower house based on population; and the Senate , an upper house based on equal representation for each state. Federalism provides substantial autonomy to the 50 states, while the country's political culture promotes liberty , equality , individualism , personal autonomy , and limited government . One of the world's most developed countries , the United States has had

5412-596: The Midwest . At the same time, about one million French Canadians migrated from Quebec to New England . During the Great Migration , millions of African Americans left the rural South for urban areas in the North. Alaska was purchased from Russia in 1867. The Compromise of 1877 effectively ended Reconstruction and white supremacists took local control of Southern politics . African Americans endured

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5544-688: The National Park Service and other agencies. About 28% of the country's land is publicly owned and federally managed, primarily in the Western States . Most of this land is protected , though some is leased for commercial use, and less than one percent is used for military purposes. Environmental issues in the United States include debates on non-renewable resources and nuclear energy , air and water pollution , biodiversity , logging and deforestation , and climate change . The U.S. Environmental Protection Agency (EPA)

5676-652: The New Deal , a series of sweeping programs and public works projects combined with financial reforms and regulations . All were intended to protect against future economic depressions. Initially neutral during World War II , the U.S. began supplying war materiel to the Allies of World War II in March 1941 and entered the war in December after the Empire of Japan 's attack on Pearl Harbor . The U.S. developed

5808-778: The Organization of American States and the United States–Mexico–Canada Free Trade Agreement . In South America, Colombia is traditionally considered to be the closest ally of the United States. The U.S. exercises full international defense authority and responsibility for Micronesia , the Marshall Islands , and Palau through the Compact of Free Association . It has increasingly conducted strategic cooperation with India , but its ties with China have steadily deteriorated. Since 2014,

5940-648: The Pentium microprocessor in accordance with Moore's law , rechargeable lithium-ion batteries , the first gene therapy trial, and cloning either emerged in the U.S. or were improved upon there. The Human Genome Project was formally launched in 1990, while Nasdaq became the first stock market in the United States to trade online in 1998. In the Gulf War of 1991, an American-led international coalition of states expelled an Iraqi invasion force that had occupied neighboring Kuwait . The September 11 attacks on

6072-534: The Soviet Union's collapse and the end of the Cold War in 1991, the U.S. emerged as the world's sole superpower , wielding significant geopolitical influence globally . The U.S. national government is a presidential constitutional federal republic and liberal democracy with three separate branches : legislative , executive , and judicial . It has a bicameral national legislature composed of

6204-591: The Spanish–American War . (The Philippines was granted full independence from the U.S. on July 4, 1946, following World War II. Puerto Rico and Guam have remained U.S. territories.) American Samoa was acquired by the United States in 1900 after the Second Samoan Civil War . The U.S. Virgin Islands were purchased from Denmark in 1917. The United States entered World War I alongside

6336-511: The White House , Department of Commerce , FAA , and the general meteorological community (private sector and the media). The short range forecasters are responsible for preparing forecasts for the time period of 6 through 60 hours. These products are issued twice daily using guidance from the NWS's Global Forecast System (GFS) and North American Mesoscale Model (NAM), as well as guidance from

6468-700: The cotton gin made the institution increasingly profitable for Southern elites . This sectional conflict regarding slavery culminated in the American Civil War (1861–1865). Eleven slave states seceded and formed the Confederate States of America , while the other states remained in the Union . War broke out in April 1861 after the Confederates bombarded Fort Sumter . After

6600-537: The fall of communism and the collapse of the Soviet Union , which marked the end of the Cold War and left the United States as the world's sole superpower . The 1990s saw the longest recorded economic expansion in American history , a dramatic decline in U.S. crime rates , and advances in technology . Throughout this decade, technological innovations such as the World Wide Web , the evolution of

6732-445: The largest nominal GDP since about 1890 and accounted for over 15% of the global economy in 2023. It possesses by far the largest amount of wealth of any country and has the highest disposable household income per capita among OECD countries. The U.S. ranks among the world's highest in economic competitiveness , productivity , innovation , human rights , and higher education . Its hard power and cultural influence have

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6864-733: The 1775 Battles of Lexington and Concord , igniting the American Revolutionary War . At the Second Continental Congress , the colonies appointed George Washington commander-in-chief of the Continental Army , and created a committee that named Thomas Jefferson to draft the Declaration of Independence . Two days after passing the Lee Resolution to create an independent nation the Declaration

6996-408: The 1775–1783 Revolutionary War , the country continued to expand westward across North America , resulting in the dispossession of native inhabitants . As more states were admitted , a North–South division over slavery led to the secession of the Confederate States of America , which fought states remaining in the Union in the 1861–1865 American Civil War . With the victory and preservation of

7128-466: The 2010s, political polarization in the country increased between liberal and conservative factions. This polarization was capitalized upon in the January 2021 Capitol attack , when a mob of insurrectionists entered the U.S. Capitol and sought to prevent the peaceful transfer of power in an attempted self-coup d'état . The United States is the world's third-largest country by total area behind Russia and Canada. The 48 contiguous states and

7260-438: The Air Force Master Analysis Center and the Navy Weather Central to create the Weather Bureau-Air Force-Navy (WBAN) Analysis Center. Their operations commenced on June 16, 1947, at 24th and M Streets NW. By early 1950 the WBAN Analysis Center consisted of 150 employees. Medium range forecasting was done nationally to 54 hours in the future. Charts and maps were created at this facility for national distribution. In July 1954,

7392-426: The American West have an alpine climate . The climate is arid in the Southwest, Mediterranean in coastal California , and oceanic in coastal Oregon , Washington , and southern Alaska . Most of Alaska is subarctic or polar . Hawaii , the southern tip of Florida and U.S. territories in the Caribbean and Pacific are tropical . States bordering the Gulf of Mexico are prone to hurricanes, and most of

7524-403: The Caribbean. [REDACTED]  This article incorporates public domain material from "Hydrometeorological Prediction Center" . National Weather Service . NOAA . United States The United States of America ( USA ), commonly known as the United States ( U.S. ) or America , is a country primarily located in North America . It is a federal union of 50 states and

7656-420: The Declaration of Independence on July 4, 1776. The term "United States" and the initialism "U.S.", used as nouns or as adjectives in English, are common short names for the country. The initialism "USA", a noun, is also common. "United States" and "U.S." are the established terms throughout the U.S. federal government , with prescribed rules. In English, the term "America" rarely refers to topics unrelated to

7788-404: The District of Columbia occupy a combined area of 3,119,885 square miles (8,080,470 km ). The coastal plain of the Atlantic seaboard gives way to inland forests and rolling hills in the Piedmont plateau region. The Appalachian Mountains and the Adirondack massif separate the East Coast from the Great Lakes and the grasslands of the Midwest . The Mississippi River System ,

7920-458: The Elder concluded that major military resources needed to be devoted to North America to win the war against France. For the first time, the continent became one of the main theaters of what could be termed a " world war ". The British colonies' position as an integral part of the British Empire became more apparent during the war, with British military and civilian officials becoming a more significant presence in American life. The war increased

8052-414: The GFS, ECMWF, Canadian, and North American Ensemble Forecast System (NAEFS). The medium range forecast products include surface pressure patterns, circulation centers and fronts, daily maximum and minimum temperatures and anomalies, probability of precipitation in 12-hour increments, total 5-day precipitation accumulation for the next five days, and 500 hPa (mb) height forecasts for days 3–7. In addition,

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8184-403: The Hurricane Hotline call with the NHC and other forecast offices and government agencies at 1700 UTC for tropical cyclones in the Atlantic Ocean basin west of 60W longitude. Also, points for days 6 and 7 for existing tropical cyclones east of 140W longitude, and days 3–7 to possible future tropical cyclones, are coordinated between the medium range pressures desk and NHC each day at 1700 UTC during

8316-465: The January 1863 Emancipation Proclamation , many freed slaves joined the Union army . The war began to turn in the Union's favor following the 1863 Siege of Vicksburg and Battle of Gettysburg , and the Confederacy surrendered in 1865 after the Union's victory in the Battle of Appomattox Court House . The Reconstruction era followed the war. After the assassination of President Abraham Lincoln , Reconstruction Amendments were passed to protect

8448-585: The Joint Numerical Weather Prediction Unit (JNWPU) was created to test out numerical weather prediction (NWP) techniques by computer . This unit co-located with the WBAN analysis center to form the National Weather Analysis Center, which was located in Suitland, Maryland . When the two units merged, the name changed to the National Meteorological Center (NMC) in January 1958. When the JNWPU dissolved in 1961, NMC became an independent organization from Global Weather Central and Fleet Numerical Weather Central . Research and computer processing abilities increased over

8580-572: The National Environmental Satellite Data and Information Service (NESDIS) is co-located with the WPC QPF desks, which together form the National Precipitation Prediction Unit (NPPU). NESDIS meteorologists prepare estimates of rainfall and current trends based on satellite data, and this information is used by the Day 1 QPF forecaster to help create individual 6-hourly forecasts that cover the next 12 hours. With access to WSR-88D/ Doppler weather radar data, satellite estimates, and NCEP model forecast data as well as current weather observations and WPC analyses,

8712-476: The Rocky Mountains, the Yellowstone Caldera , is the continent's largest volcanic feature. In 2021, the United States had 8% of global permanent meadows and pastures and 10% of cropland. With its large size and geographic variety, the United States includes most climate types. East of the 100th meridian , the climate ranges from humid continental in the north to humid subtropical in the south. The western Great Plains are semi-arid . Many mountainous areas of

8844-451: The U.S. has become a key ally of Ukraine ; it has also provided the country with significant military equipment and other support in response to Russia's 2022 invasion . The president is the commander-in-chief of the United States Armed Forces and appoints its leaders, the secretary of defense and the Joint Chiefs of Staff . The Department of Defense , which is headquartered at the Pentagon near Washington, D.C., administers five of

8976-661: The U.S. territories." Despite disparate systems of confinement, four main institutions dominate: federal prisons , state prisons , local jails, and juvenile correctional facilities . Federal prisons are run by the Federal Bureau of Prisons and hold people who have been convicted of federal crimes, including pretrial detainees. State prisons, run by the official department of correction of each state, hold sentenced people serving prison time (usually longer than one year) for felony offenses. Local jails are county or municipal facilities that incarcerate defendants prior to trial; they also hold those serving short sentences (typically under

9108-416: The United States and the peaceful transfer of power , respectively. The Louisiana Purchase of 1803 from France nearly doubled the territory of the United States. Lingering issues with Britain remained , leading to the War of 1812 , which was fought to a draw. Spain ceded Florida and its Gulf Coast territory in 1819. In the late 18th century, American settlers began to expand westward , many with

9240-541: The United States entered the Cold War, where geopolitical tensions between the U.S. and the Soviet Union led the two countries to dominate world affairs . The U.S. utilized the policy of containment to limit the USSR's sphere of influence, and prevailed in the Space Race , which culminated with the first crewed Moon landing in 1969. Domestically, the U.S. experienced economic growth , urbanization , and population growth following World War II . The civil rights movement emerged, with Martin Luther King Jr. becoming

9372-495: The United States has operated as a de facto two-party system , though the parties in that system have been different at different times. The two main national parties are presently the Democratic and the Republican . The former is perceived as relatively liberal in its political platform while the latter is perceived as relatively conservative . In the American federal system , sovereign powers are shared between two levels of elected government: national and state. People in

9504-593: The United States in 2001 by the pan-Islamist militant organization al-Qaeda led to the war on terror , and subsequent military interventions in Afghanistan and Iraq . The cultural impact of the attacks was profound and long-lasting. The U.S. housing bubble culminated in 2007 with the Great Recession , the largest economic contraction since the Great Depression. Coming to a head in

9636-597: The United States of America to Spain" to seek assistance in the Revolutionary War effort. The first known public usage is an anonymous essay published in the Williamsburg newspaper, The Virginia Gazette , on April 6, 1776. By June 1776, the "United States of America" appeared in the Articles of Confederation and the Declaration of Independence . The Second Continental Congress adopted

9768-601: The United States, slavery was abolished nationally . By 1900, the country had established itself as a great power , a status solidified after its involvement in World War I . After Japan 's attack on Pearl Harbor in December 1941, the U.S. entered World War II . Its aftermath left the U.S. and the Soviet Union as the world's two superpowers and led to the Cold War , during which both countries struggled for ideological dominance and international influence . Following

9900-541: The United States, despite the usage of "the Americas " as the totality of North and South America. "The States" is an established colloquial shortening of the name, used particularly from abroad; "stateside" is the corresponding adjective or adverb. The first inhabitants of North America migrated from Siberia across the Bering land bridge about 12,000 years ago; the Clovis culture , which appeared around 11,000 BC,

10032-624: The United States, except Iran , North Korea , and Bhutan . Though Taiwan does not have formal diplomatic relations with the U.S., it maintains close unofficial relations. The United States regularly supplies Taiwan with military equipment to deter potential Chinese aggression. Its geopolitical attention also turned to the Indo-Pacific when the United States joined the Quadrilateral Security Dialogue with Australia, India, and Japan. The United States has

10164-509: The United States. The American prison system is largely heterogenous, with thousands of relatively independent systems operating across federal, state, local, and tribal levels. In 2023, "these systems [held] almost 2 million people in 1,566 state prisons, 98 federal prisons, 3,116 local jails, 1,323 juvenile correctional facilities, 181 immigration detention facilities, and 80 Indian country jails, as well as in military prisons , civil commitment centers, state psychiatric hospitals, and prisons in

10296-542: The WPC has several other routine duties pertaining to tropical weather forecasting. Through 2008, WPC provided track forecast guidance to the NHC whenever there is a tropical cyclone in the Atlantic Ocean basin west of 60W longitude. As required, this guidance is provided to the NHC four times daily for use in the tropical cyclone package issued by the NHC at 0300 UTC, 0900 UTC, 1500 UTC and 2100 UTC. The WPC participates in

10428-524: The Weather Prediction Center. The mission of the WPC is to provide forecast, guidance, and analysis products and services to support the daily public forecasting activities of the NWS and its customers, and to provide tailored support to other government agencies in emergency and special situations. The QPF desks prepare and issue forecasts of accumulating (quantitative) precipitation, heavy rain, heavy snow, and highlights areas with

10560-490: The center since 1973. Short-term forecasts are made at the meteorological watch (metwatch) desk. It issues mesoscale precipitation discussions (MPDs) as flash flood guidance for NWS forecast offices (NWSFOs), NWS River Forecast Centers (RFCs), the media, emergency managers, and other users. MPDs contain technical discussions concerning heavy rainfall events and expected impacts on flash flooding. They are ideally issued 1–6 hours preceding an event, include graphical descriptions of

10692-457: The contiguous United States are in the State of California, about 84 miles (135 km) apart. At an elevation of 20,310 feet (6,190.5 m), Alaska's Denali is the highest peak in the country and continent. Active volcanoes are common throughout Alaska's Alexander and Aleutian Islands , and Hawaii consists of volcanic islands. The supervolcano underlying Yellowstone National Park in

10824-497: The contiguous United States (CONUS) and issued from September 15 to May 15 each cold season. Graphical forecasts are issued twice daily at 0900 UTC and 2100 UTC (4AM/PM EST respectively), although updates may be warranted by rapidly changing conditions. The Winter Weather Desk issues probabilistic heavy snow and icing guidance products for the next three days. The forecasts represent the probability that freezing rain or combined snow/sleet accumulations will meet specific criteria within

10956-556: The country's GDP. The U.S. has 42% of the world's nuclear weapons —the second-largest share after Russia. The United States has the third-largest combined armed forces in the world, behind the Chinese People's Liberation Army and Indian Armed Forces . The military operates about 800 bases and facilities abroad, and maintains deployments greater than 100 active duty personnel in 25 foreign countries. State defense forces (SDFs) are military units that operate under

11088-469: The country's territory would expand with the admission of new states , rather than the expansion of existing states. The U.S. Constitution was drafted at the 1787 Constitutional Convention to overcome the limitations of the Articles. It went into effect in 1789, creating a federal republic governed by three separate branches that together ensured a system of checks and balances . George Washington

11220-515: The details and the area covered. Their size typically is about half the size of Kansas. There are three headlines ordered by severity: "flash flooding likely", "flash flooding possible", or "flash flooding unlikely". Mesoscale discussions (MDs) once were issued by the Storm Prediction Center (SPC) for both convective (MCDs) and precipitation (MPDs) events but WPC now covers this heavy rainfall function. The International desks have

11352-713: The development of self-governance, and the First Great Awakening , a series of Christian revivals , fueled colonial interest in religious liberty . For a century, the American colonists had been providing their own troops and materiel in conflicts with indigenous peoples allied with Britain's colonial rivals , especially France, and the Americans had begun to develop a sense of self-defense and self-reliance separate from Britain. The French and Indian War (1754–1763) took on new significance for all North American colonists after Parliament under William Pitt

11484-567: The early days of organized weather collection in the United States, a central facility was used to gather and disseminate data. Originally, this task occupied a single room within the United States Army Signal Service in Washington, D.C. Reports were collected via telegraph and general forecasts were made for the country. While WPC's roots lie deep in the past, the organization can be most directly traced to

11616-475: The ensemble. The PME is quick to produce, and is available through their Water and the Land page on their website. The Hong Kong Observatory generates short term rainstorm warnings for systems which are expected to accumulate a certain amount of rainfall per hour over the next few hours. They use three levels of warning. The amber warning indicates that a rainfall intensity of 30 millimetres (1.2 in) per hour

11748-580: The environment for labor unions to begin to flourish . This period eventually ended with the advent of the Progressive Era , which was characterized by significant reforms. Pro-American elements in Hawaii overthrew the Hawaiian monarchy ; the islands were annexed in 1898. That same year, Puerto Rico , the Philippines , and Guam were ceded to the U.S. by Spain after the latter's defeat in

11880-541: The federal government often applied policies of Indian removal or assimilation . The Trail of Tears (1830–1850) was a U.S. government policy that forcibly removed and displaced most Native Americans living east of the Mississippi River to lands far to the west. These and earlier organized displacements prompted a long series of American Indian Wars west of the Mississippi. The Republic of Texas

12012-606: The first nuclear weapons and used them against the Japanese cities of Hiroshima and Nagasaki in August 1945, ending the war. The United States was one of the " Four Policemen " who met to plan the post-war world , alongside the United Kingdom , Soviet Union , and China . The U.S. emerged relatively unscathed from the war, with even greater economic power and international political influence . After World War II,

12144-430: The forecast process at some point in the future, there is currently still a need for human intervention. The forecasting of the precipitation within the next six hours is often referred to as nowcasting . In this time range it is possible to forecast smaller features such as individual showers and thunderstorms with reasonable accuracy, as well as other features too small to be resolved by a computer model. A human given

12276-401: The forecaster has the latest data for use in preparation of short-range precipitation forecasts. Meteorological reasoning discussions are regularly written and issued with the forecast packages to explain and support the forecast. The WPC Winter Weather Desk issues heavy snow and icing forecast products, which support the NWS winter weather watch/warning/outlook program. These forecasts are for

12408-694: The formation of the Analysis Center by Circular Letter 39-42, signed by Weather Bureau Director Francis W. Reichelderfer on March 5, 1942. Operations began on March 16, 1942, with the unit collocated with the Weather Bureau Central Office at 24th and M Streets NW in Washington, D.C. Initially the unit was sometimes referred to as the Master Analysis Center. In 1947, the Analysis Center was combined with

12540-536: The future, forecasting amounts equal to or greater than 0.01 inches (0.25 mm). Starting in the mid-to-late 1990s, QPFs were used within hydrologic forecast models to simulate impact of rainfall on river stages. Rainfall forecasts can be verified a number of ways. Rain gauge observations can be gridded into areal averages, which are then compared to the grids for the forecast models. Weather radar estimates can be used outright, or corrected for rain gauge observations. Several statistical scores can be based on

12672-542: The future. Surface pressure forecasts are issued three times per day, with temperature and probability of precipitation products issued twice per day, using guidance from the NWS medium range forecast model (GFS) as well as models from the European Centre for Medium Range Weather Forecasting (ECMWF), the United Kingdom's Meteorology Office (UKMET), Canadian model, the Navy NOGAPS model, and ensemble guidance from

12804-633: The hurricane season. This coordination call began between the Extended Forecast Section and the Miami Hurricane Warning Office prior to 1959. Within the WPC tropical program, the lead forecaster on shift, who prepares the day 1 QPF, is to provide the rainfall statement for tropical cyclones that are expected to make landfall. This statement is included in the Public Advisory issued by the NHC, and

12936-556: The initialization of the NAM and GFS, a review of model trends and biases, and a description of model differences and preferences. The meteorologist reviews how the suite of models from the latest forecast cycle differ from each other in their forecasts of significant features, and makes a preference based upon all relevant current information. The WPC Surface Analysis is part of the NWS Unified Surface Analysis and

13068-463: The integration of Army National Guard units and personnel into the U.S. Army and (since 1947) the U.S. Air Force. There are about 18,000 U.S. police agencies from local to national level in the United States. Law in the United States is mainly enforced by local police departments and sheriff departments in their municipal or county jurisdictions. The state police departments have authority in their respective state , and federal agencies such as

13200-406: The latest radar, satellite and observational data will be able to make a better analysis of the small scale features present and so will be able to make a more accurate forecast for the following few hours. However, there are now expert systems using those data and mesoscale numerical model to make better extrapolation, including evolution of those features in time. The detail that can be given in

13332-648: The lay person. Professionals can use knowledge of local effects which may be too small in size to be resolved by the model to add information to the forecast. As an example, terrain is considered in the QPF process by using topography or climatological precipitation patterns from observations with fine detail. Using model guidance and comparing the various forecast fields to climatology, extreme events such as excessive precipitation associated with later flood events lead to better forecasts. While increasing accuracy of forecast models implies that humans may no longer be needed in

13464-401: The mid-to-late 1990s, QPFs were used within hydrologic forecast models to simulate impact to rivers throughout the United States. Forecast models show significant sensitivity to humidity levels within the planetary boundary layer , or in the lowest levels of the atmosphere, which decreases with height. QPF can be generated on a quantitative, forecasting amounts, or a qualitative, forecasting

13596-482: The military draft (leading to the end of conscription in 1973) and wide opposition to U.S. intervention in Vietnam (with the U.S. totally withdrawing in 1975). A societal shift in the roles of women was significantly responsible for the large increase in female paid labor participation during the 1970s, and by 1985 the majority of American women aged 16 and older were employed. The late 1980s and early 1990s saw

13728-612: The most attractive to the population are the most vulnerable. The U.S. is one of 17 megadiverse countries containing large numbers of endemic species : about 17,000 species of vascular plants occur in the contiguous United States and Alaska, and over 1,800 species of flowering plants are found in Hawaii, few of which occur on the mainland. The United States is home to 428 mammal species, 784 birds, 311 reptiles, 295 amphibians , and around 91,000 insect species. There are 63 national parks , and hundreds of other federally managed parks, forests, and wilderness areas , managed by

13860-541: The most likely forecast for Alaska and surrounding areas valid from four to eight days into the future. The Alaska medium range discussion, 500 hPa height graphics, and surface fronts and pressures graphics for days 4–8 are issued once per day, year-round. Additionally, gridded guidance for the forecast period is issued for the following fields: maximum/minimum temperature grids, twelve-hour probability of precipitation grids, as well as derived dewpoint temperature, cloud cover, precipitation type, and wind speed/direction grids at

13992-662: The most violent, the California genocide of thousands of Native inhabitants, lasted into the early 1870s, just as additional western territories and states were created. During the colonial period, slavery had been legal in the American colonies , though the practice began to be significantly questioned during the American Revolution. States in the North enacted abolition laws , though support for slavery strengthened in Southern states , as inventions such as

14124-521: The observations and insufficient sampling). The range of different forecasts produced can then assess the uncertainty in the forecast. Ensemble forecasts are increasingly being used for operational weather forecasting (for example at European Centre for Medium-Range Weather Forecasts (ECMWF), National Centers for Environmental Prediction (NCEP), and the Canadian Forecasting Center). Ensemble mean forecasts for precipitation have

14256-401: The observed and forecast fields. One, known as a bias , compares the size of the forecast field to the observed field, with the goal of a score of 1. The threat score involves the intersection of the forecast and observed sets, with a maximum possible verification score of 1. The probability of detection , or POD, is found by dividing the overlap between the forecast and observed fields by

14388-408: The policy of redlining later adopted by the federal Home Owners' Loan Corporation . An explosion of technological advancement accompanied by the exploitation of cheap immigrant labor led to rapid economic expansion during the late 19th and early 20th centuries , allowing the United States to outpace the economies of England, France, and Germany combined. This fostered the amassing of power by

14520-557: The potential for flash flooding, with forecasts valid over the following five days. These products are sent to the National Weather Service forecast offices and are available on the Internet for public use. Heavy snow forecast products, in association with the short-range public forecast products (described below), serve as a coordinating mechanism for the national winter storm watch and warning program. One desk of

14652-574: The primary colonial grievances was a denial of their rights as Englishmen , particularly the right to representation in the British government that taxed them . To demonstrate their dissatisfaction and resolve, the First Continental Congress met in 1774 and passed the Continental Association , a colonial boycott of British goods that proved effective. The British attempt to then disarm the colonists resulted in

14784-426: The probabilities of certain rainfall amounts being met. This allows the forecaster to assign the degree of uncertainty to the forecast. This technique is considered to be informative, relative to climatology. This method has been used for years within National Weather Service forecasts, as a period's chance of rain equals the chance that 0.01 inches (0.25 mm) will fall in any particular spot. In this case, it

14916-468: The probability of a specific amount, basis. Radar imagery forecasting techniques show higher skill than model forecasts within 6 to 7 hours of the time of the radar image. The forecasts can be verified through use of rain gauge measurements, weather radar estimates, or a combination of both. Various skill scores can be determined to measure the value of the rainfall forecast. Algorithms exist to forecast rainfall based on short term radar trends, within

15048-530: The product is meteorologically consistent. The WPC is the official backup center to the National Hurricane Center (NHC). In this capacity, the WPC is responsible for issuing all tropical cyclone products, including discussions, graphics and watches and warnings that would normally be issued by the NHC for any tropical system in the Atlantic Ocean, if NHC is unable to so. During the tropical weather season which runs from May 15 – November 30,

15180-495: The responsibility of the National Hurricane Center . The Weather Prediction Center also acts as the backup office to the National Hurricane Center in the event of a complete communications failure. Long range climatological forecasts are produced by the Climate Prediction Center (CPC), a branch of the National Weather Service. These include 8–14 day outlooks, monthly outlooks, and seasonal outlooks. From

15312-570: The rights of African Americans . National infrastructure, including transcontinental telegraph and railroads , spurred growth in the American frontier . From 1865 through 1917 an unprecedented stream of immigrants arrived in the United States, including 24.4 million from Europe. Most came through the port of New York City , and New York City and other large cities on the East Coast became home to large Jewish , Irish , and Italian populations, while many Germans and Central Europeans moved to

15444-614: The rocky Great Basin and Chihuahua , Sonoran , and Mojave deserts. In the northwest corner of Arizona , carved by the Colorado River over millions of years, is the Grand Canyon , a steep-sided canyon and popular tourist destination known for its overwhelming visual size and intricate, colorful landscape. The Sierra Nevada and Cascade mountain ranges run close to the Pacific coast . The lowest and highest points in

15576-482: The same problems associated with their use in other fields, as they average out more extreme values, and therefore have limited usefulness for extreme events. In the case of the SREF ensemble mean, used within the United States, this decreasing usefulness starts with values as low as 0.50 inches (13 mm). In addition to graphical rainfall forecasts showing quantitative amounts, rainfall forecasts can be made describing

15708-573: The six service branches, which are made up of the U.S. Army , Marine Corps , Navy , Air Force , and Space Force . The Coast Guard is administered by the Department of Homeland Security in peacetime and can be transferred to the Department of the Navy in wartime. The United States spent $ 916 billion on its military in 2023, which is by far the largest amount of any country , making up 37% of global military spending and accounting for 3.4% of

15840-427: The size of the observed field: the goal here is a score of 1. The critical success index, or CSI, divides the overlap between the forecast and observed fields by the combined size of the forecast and observed fields: the goal here is a score of 1. The false alarm rate , or FAR, divides the area of the forecast which does not overlap the observed field by the size of the forecasted area. The goal value in this measure

15972-545: The sole authority of a state government. SDFs are authorized by state and federal law but are under the command of the state's governor . They are distinct from the state's National Guard units in that they cannot become federalized entities. A state's National Guard personnel, however, may be federalized under the National Defense Act Amendments of 1933 , which created the Guard and provides for

16104-543: The states are also represented by local elected governments , which are administrative divisions of the states. States are subdivided into counties or county equivalents , and further divided into municipalities . The District of Columbia is a federal district containing the U.S. capital, Washington, D.C. . The federal district is an administrative division of the federal government. Federally recognized tribes govern 326 Indian reservations . The United States has an established structure of foreign relations, and it has

16236-451: The structure and responsibilities of the national federal government and its relationship with the individual states. The U.S. Constitution is the world's oldest national constitution still in effect (from March 4, 1789). Composed of three branches, all headquartered in Washington, D.C., the federal government is the national government of the United States. It is regulated by a strong system of checks and balances . The three-branch system

16368-582: The world's fourth-longest river system , runs predominantly north–south through the heart of the country. The flat and fertile prairie of the Great Plains stretches to the west, interrupted by a highland region in the southeast. The Rocky Mountains , west of the Great Plains, extend north to south across the country, peaking at over 14,000 feet (4,300 m) in Colorado . Farther west are

16500-583: The world's second-largest diplomatic corps as of 2024 . It is a permanent member of the United Nations Security Council , and home to the United Nations headquarters . The United States is a member of the G7 , G20 , and OECD intergovernmental organizations. Almost all countries have embassies and many have consulates (official representatives) in the country. Likewise, nearly all countries host formal diplomatic missions with

16632-444: The world's oldest surviving federation, and its presidential system of national government has been adopted, in whole or in part, by many newly independent states worldwide following their decolonization . It is a liberal representative democracy "in which majority rule is tempered by minority rights protected by law ". The Constitution of the United States serves as the country's supreme legal document , also establishing

16764-553: The world's tornadoes occur in the country , mainly in Tornado Alley . Overall, the United States receives more high-impact extreme weather incidents than any other country. Extreme weather became more frequent in the U.S. in the 21st century, with three times the number of reported heat waves as in the 1960s. In the American Southwest , droughts became more persistent and more severe. The regions considered as

16896-557: The world, with almost 2 million people incarcerated . An analysis of the World Health Organization Mortality Database from 2010 showed U.S. homicide rates "were 7 times higher than in other high-income countries, driven by a gun homicide rate that was 25 times higher". Quantitative precipitation forecast The quantitative precipitation forecast (abbreviated QPF ) is the expected amount of melted precipitation accumulated over

17028-541: The years, which allowed for the first global forecast model to run by June 1966. By January 1975, much of the facility, minus the computers, moved to the World Weather Building, located in nearby Camp Springs, Maryland . NMC changed its name to NCEP, the National Centers for Environmental Prediction on October 1, 1995. The Hydrometeorological Prediction Center became a subunit of NCEP, as did

17160-575: Was annexed in 1845, and the 1846 Oregon Treaty led to U.S. control of the present-day American Northwest . Victory in the Mexican–American War resulted in the 1848 Mexican Cession of California, Nevada, Utah, and much of present-day Colorado and the American Southwest . The California gold rush of 1848–1849 spurred a huge migration of white settlers to the Pacific coast, leading to even more confrontations with Native populations. One of

17292-759: Was adopted on July 4, 1776. The political values of the American Revolution included liberty , inalienable individual rights ; and the sovereignty of the people ; supporting republicanism and rejecting monarchy , aristocracy , and all hereditary political power; civic virtue ; and vilification of political corruption . The Founding Fathers of the United States , who included Washington, Jefferson, John Adams , Benjamin Franklin , Alexander Hamilton , John Jay , James Madison , Thomas Paine , and many others, were inspired by Greco-Roman , Renaissance , and Enlightenment philosophies and ideas. The Articles of Confederation were ratified in 1781 and established

17424-583: Was elected the country's first president under the Constitution, and the Bill of Rights was adopted in 1791 to allay skeptics' concerns about the power of the more centralized government. His resignation as commander-in-chief after the Revolutionary War and his later refusal to run for a third term as the country's first president established a precedent for the supremacy of civil authority in

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