A tornado warning is a public warning that is issued by weather forecasting agencies to an area in the direct path of a tornado, or a severe thunderstorm capable of producing one, and advises individuals in that area to take cover. Modern weather surveillance technology such as Doppler weather radar can detect rotation in a thunderstorm, allowing for early warning before a tornado develops. They are also commonly issued based on reported visual sighting of a tornado, funnel cloud, or wall cloud, typically from weather spotters or the public, but also law enforcement or local emergency management. When radar is unavailable or insufficient, such ground truth is crucial. In particular, a tornado can develop in a gap of radar coverage, of which there are several known in the United States.
A severe thunderstorm warning is a type of public warning for severe weather that is issued by weather forecasting agencies worldwide when one or more severe thunderstorms have been detected by Doppler weather radar, observed by weather spotters, or reported by an emergency management agency, law enforcement, or the general public. Unlike a watch, a warning is issued to areas in the direct path of active severe thunderstorms, that are expecting a direct impact typically within an hour. Severe thunderstorms can cause property damage and injury due to large hail, high winds, and flooding due to torrential rainfall. The exact criteria to issue a warning varies from country to country.
A winter storm warning is a hazardous weather statement issued by Weather Forecast Offices (WFO) of the National Weather Service (NWS) in the United States to alert the public that a winter storm is occurring or is about to occur in the area, usually within 36 hours of the storm's onset.
This article describes severe weather terminology used by the National Weather Service (NWS) in the United States. The NWS is a government agency operating as an arm of the National Oceanic and Atmospheric Administration (NOAA) branch. It defines precise meanings for nearly all of its weather terms.
A snow squall warning is a bulletin issued by Environment Canada's Meteorological Service of Canada and the National Weather Service in the United States to warn population of two types of snow events reducing visibility in blowing snow: lake effectsnow squalls and frontal snow squalls.
In weather forecasting in the United States, "particularly dangerous situation" (PDS) is enhanced wording used by the National Weather Service to convey special urgency in some watch or warning messages for unusually extreme and life-threatening severe weather events, above and beyond the average severity for the type of event. It is used in the format "This is a particularly dangerous situation..." at the discretion of the issuing forecaster. A watch or warning bearing the phrase is referred to as a PDS watch or PDS warning as shorthand jargon.
A tornado emergency is an enhanced version of a tornado warning, which is used by the National Weather Service (NWS) in the United States during imminent, significant tornado occurrences in highly populated areas. Although it is not a new warning type from the NWS, issued instead within a severe weather statement or in the initial tornado warning, a tornado emergency generally means that significant, widespread damage is expected to occur and a high likelihood of numerous fatalities is expected with a large, strong to violent tornado.
A flash flood watch is severe weather watch product of the National Weather Service that is issued when conditions are favorable for flash flooding in flood-prone areas, usually when grounds are already saturated from recent rains, or when upcoming rains will have the potential to cause a flash flood. These watches are also occasionally issued when a dam may break in the near future.
A flood warning is closely linked to the task of flood forecasting. The distinction between the two is that the outcome of flood forecasting is a set of forecast time-profiles of channel flows or river levels at various locations, while "flood warning" is the task of making use of these forecasts to make decisions about whether warnings of floods should be issued to the general public or whether previous warnings should be rescinded or retracted.
From May 3 to May 11, 2003, a prolonged and destructive series of tornado outbreaks affected much of the Great Plains and Eastern United States. Most of the severe activity was concentrated between May 4 and May 10, which saw more tornadoes than any other week-long span in recorded history; 335 tornadoes occurred during this period, concentrated in the Ozarks and central Mississippi River Valley. Additional tornadoes were produced by the same storm systems from May 3 to May 11, producing 363 tornadoes overall, of which 62 were significant. Six of the tornadoes were rated F4, and of these four occurred on May 4, the most prolific day of the tornado outbreak sequence; these were the outbreak's strongest tornadoes. Damage caused by the severe weather and associated flooding amounted to US$4.1 billion, making it the costliest U.S. tornado outbreak of the 2000s. A total of 50 deaths and 713 injuries were caused by the severe weather, with a majority caused by tornadoes; the deadliest tornado was an F4 that struck Madison and Henderson counties in Tennessee, killing 11. In 2023, tornado expert Thomas P. Grazulis created the outbreak intensity score (OIS) as a way to rank various tornado outbreaks. The tornado outbreak sequence of May 2003 received an OIS of 232, making it the fourth worst tornado outbreak in recorded history.
On August 4, 2009, a flash flood occurred and impacted Louisville and portions of the surrounding Kentuckiana region as a cold front and mesoscale convective system moved across the Midwestern United States. The National Weather Service estimated that between three and six inches of rain fell across the city in less than one hour, breaking all previous one-hour rainfall records in the area. Most of the downtown area was underwater, with the deluge reaching four feet (1.2 m) deep in places.
An urban and small stream flood advisory is issued when ponding of water of streets, low-lying areas, highways, underpasses, urban storm drains, and elevation of creek and small stream levels is occurring or imminent. Urban and small stream flood advisories are issued for flooding that occurs within three hours after the excessive rainfall. These advisories are issued on a county by county basis by the local Weather Forecast Office and are generally in effect for 3 to 4 hours.
A river flood warning is issued by the National Weather Service of the United States when forecast points with formal river gaging sites and established flood stages along rivers, where flooding has already been forecast, is imminent or occurring. The National Weather Service defines river flooding as "the inundation of normally dry areas as a result of increased water levels in an established water course."
This page documents notable tornadoes and tornado outbreaks worldwide in 2020. Strong and destructive tornadoes form most frequently in the United States, Argentina, Brazil, Bangladesh, and eastern India, but can occur almost anywhere under the right conditions. Tornadoes also develop occasionally in southern Canada during the Northern Hemisphere's summer and somewhat regularly at other times of the year across Europe, Asia, Argentina, Australia and New Zealand. Tornadic events are often accompanied by other forms of severe weather, including strong thunderstorms, strong winds, and hail. There were 1,243 preliminary filtered reported tornadoes in 2020 in the United States in 2020, and 1,086 confirmed tornadoes in the United States in 2020. Worldwide, at least 93 tornado-related deaths were confirmed with 78 in the United States, eight in Vietnam, two each in Canada, Indonesia, and Mexico, and one in South Africa.
Hurricane Laura was a deadly and destructive Category 4 hurricane that is tied with the 1856 Last Island hurricane and 2021's Hurricane Ida as the strongest hurricane on record to make landfall in the U.S. state of Louisiana, as measured by maximum sustained winds. The twelfth named storm, fourth hurricane, and first major hurricane of the record-breaking 2020 Atlantic hurricane season, Laura originated from a large tropical wave that moved off the West African coast on August 16 and became a tropical depression on August 20. Laura intensified into a tropical storm a day later, becoming the earliest twelfth named storm on record in the North Atlantic basin, forming eight days earlier than 1995's Hurricane Luis.
Hurricane Sally was a destructive and slow-moving Atlantic hurricane that was the first hurricane to make landfall in the U.S. state of Alabama since Ivan in 2004, coincidentally on the same date in the same place. The eighteenth named storm and seventh hurricane of the extremely active 2020 Atlantic hurricane season, Sally developed from an area of disturbed weather which was first monitored over the Bahamas on September 10. The system grew a broad area of low-pressure on September 11, and was designated as a tropical depression late that day. Early the next day, the depression made landfall at Key Biscayne and subsequently strengthened into Tropical Storm Sally that afternoon. Moderate northwesterly shear prevented significant intensification for the first two days, but convection continued to grow towards the center and Sally slowly intensified. On September 14, a center reformation into the center of the convection occurred, and data from a hurricane hunter reconnaissance aircraft showed that Sally had rapidly intensified into a strong Category 1 hurricane. However, an increase in wind shear and upwelling of colder waters halted the intensification and Sally weakened slightly on September 15 before turning slowly northeastward. Despite this increase in wind shear, it unexpectedly re-intensified, reaching Category 2 status early on September 16 before making landfall at peak intensity at 09:45 UTC on September 16, near Gulf Shores, Alabama, with maximum sustained winds of 110 mph (180 km/h) and a minimum central pressure of 965 millibars (28.5 inHg). The storm rapidly weakened after landfall before transitioning into an extratropical low at 12:00 UTC the next day. Sally's remnants lasted for another day as they moved off the coast of the Southeastern United States before being absorbed into another extratropical storm on September 18.
Tropical Storm Beta was a tropical cyclone that brought heavy rainfall, flooding, and severe weather to the Southeastern United States in September 2020. The twenty-third tropical depression and twenty-third named storm of the record-breaking 2020 Atlantic hurricane season, Beta originally formed from a trough of low pressure that developed in the northeastern Gulf of Mexico on September 10. The low moved slowly southwestward, with development hampered initially by the development of nearby Hurricane Sally. After Sally moved inland over the Southeastern United States and weakened, the disturbance became nearly stationary in the southwestern Gulf, where it began to organize. By September 16, the storm had gained a low-level circulation center and had enough organization to be designated as Tropical Depression Twenty-Two. The system held its intensity for a day due to the influence of strong wind shear and dry air, before eventually attaining tropical storm strength. It slowly moved northward and intensified to a mid-range tropical storm before dry air and wind shear halted its intensification. Beta then became nearly stationary on September 19, before starting to move west towards the Texas coast the next day, weakening as it approached. On September 21, Beta made landfall near Matagorda Peninsula, Texas as a minimal tropical storm. It subsequently weakened to a tropical depression the next day before becoming post-tropical early on September 23. Its remnants moved northeastward, before the center elongated and merged with a cold front early on September 25.
A significant tornado outbreak sequence took place from March 24–28, 2021 in the Southern United States, just one week after another outbreak affected similar regions. There were 43 tornadoes confirmed across 11 states, with the bulk of activity primarily on March 25, which resulted in the Storm Prediction Center (SPC) issuing its second high-risk outlook for the month of March, as well as the second high-risk outlook for 2021. Several intense tornadoes touched down on that day, including ones that prompted the issuance of rare tornado emergencies near Hoover, Alabama, Brent and Centreville, Alabama, and in the Newnan, Georgia area. March 27 also saw widespread tornado activity mainly across East Texas, Southern Arkansas, Louisiana, and Western Tennessee with several strong tornadoes touching down. Scattered to widespread wind and hail damage occurred throughout the outbreak sequence, and repeated rounds of heavy rain caused widespread severe flash and river flooding across much of Tennessee.
