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===Weather warnings and advisories=== {{Main|Severe weather terminology (United States)}} Short-fused [[weather warning]]s and advisories issued by local NWS forecast offices are generally less than {{convert|500|-|5000|sqmi|km2}} in area. Warnings for severe local storms are intended to be issued preceding the arrival of severe weather at a particular locale by one hour or less; the NWS also issues warnings and advisories for various hydrological and non-hydrological events including [[flood]]s, non-thunderstorm high winds, [[winter storm]]s, intense heat or cold, fire weather and marine hazards, which vary in timepsan depending on the weather situation ([[Tropical cyclone warnings and watches|inland and coastal warnings for tropical cyclones]] are issued by the [[National Hurricane Center]] (NHC), a guidance center of the National Oceanic and Atmospheric Administration). The NWS defines a warning as a "hazardous weather or hydrologic event [that] is occurring, is imminent, or has a very high probability of occurring" and an advisory as "[highlighting] special weather conditions that are less serious than a warning [...] for events that may cause significant inconvenience, and if caution is not exercised, [..] could lead to situations that may threaten life and/or property."<ref>{{cite web|title=National Weather Service Glossary: W|url=http://www.weather.gov/glossary/index.php?letter=w|website=National Weather Service|publisher=National Oceanic and Atmospheric Administration|access-date=May 26, 2017}}</ref><ref>{{cite web|title=National Weather Service Glossary: A|url=http://w1.weather.gov/glossary/index.php?letter=a|website=National Weather Service|publisher=National Oceanic and Atmospheric Administration|access-date=May 26, 2017}}</ref> In earnest, they indicate that hazardous weather conditions are occurring that may pose a risk to life and property, and are intended to direct the general public to take immediate action and heed safety precautions; it also has the side purpose of directing emergency management personnel to be on standby in case the weather situation leads to property damage or casualties. Severe thunderstorm and flood warnings indicate that organized severe thunderstorms or flooding are occurring, whereas tornado warnings are issued if a storm is indicated to be producing an observed tornado or exhibits strong, low-level rotation.<ref>{{cite web|title=Watch vs. Warning: What's the Difference|url=https://www.weatherworksinc.com/watch-vs-warning|website=WeatherWorks|date=June 6, 2016}}</ref> The process of issuing a warning or advisory begins with observations of a hydrological or [[extreme weather]] event that is either occurring at present (through radar imagery, reports from local television and radio stations, or ground observations by local law enforcement, civil defense officials, media outlets or storm spotters) or is forecast to occur within 12 to 24 hours. If after collaboration a warning or advisory is deemed necessary, the Weather Forecast Office will generate a bulletin product via the Advance Weather Interactive Processing System ([[AWIPS]]) and then disseminate the alert through various communication routes accessed by the media and various agencies, on the internet, to [[National Oceanic and Atmospheric Administration|NOAA]] satellites, and on [[NOAA Weather Radio]].<ref name="Dissemination">{{cite web|title=NWS Dissemination Services|url=http://www.nws.noaa.gov/om/disemsys.shtml|url-status=dead|archive-url=https://archive.today/20121212124935/http://www.nws.noaa.gov/om/disemsys.shtml|archive-date=December 12, 2012|access-date=January 10, 2010|website=NWS Office of Climate, Water, and Weather Services|publisher=National Oceanic and Atmospheric Administration}}</ref> The product outlines the alert type, the issuing WFO, the sections of government subdivisions ([[County (United States)|counties]], [[Parish (administrative division)|parishes]], [[borough]]s or [[Independent city (United States)|independent cities]]) covered by the alert, and its time of expiration (based on the local [[time zone]]). Some products β particularly for severe thunderstorm, tornado and flood warnings β include a tag requesting [[Emergency Alert System]] activation to trigger public alert messages via television, radio stations, NOAA Weather Radio, and smartphone apps and messaging services. For local storm events, the warning or advisory product also outlines a meteorological summary of the most recent storm location or local storm report issued prior to the product's issuance (including the approximate area in [[statute mile]]s and estimated speed and direction), associated hazards, impacts, municipalities and designated land areas (and, if applicable, highway mile markers) covered by the alert, and boilerplate action messages informing the public of safety precautions they need to take or advising them to be vigilant of any warnings or weather statements that may be issued by their local National Weather Service office. A statement may be issued as a follow-up message to a warning, watch, or emergency, which may update, extend, or cancel the previously issued product or be used as a notification of significant weather for which no type of alert is currently in effect for a given location or is expected to be in effect. In situations where a forecaster indicates a significant threat of extremely severe and life-threatening weather with an ongoing local weather event, enhanced wording may be used to note the heightened threat by a significant local storm event. In April 2012, the NWS introduced the Impact Based Warning system at its Weather Forecast Offices in [[Wichita, Kansas|Wichita]] and [[Topeka, Kansas|Topeka]], [[Kansas]], and [[Springfield, Missouri|Springfield]], [[St. Louis, Missouri|St. Louis]] and [[Kansas City, Missouri|Kansas City]]/[[Pleasant Hill, Missouri|Pleasant Hill]], [[Missouri]]; the pilot project β which would expand to 80 Weather Forecast Offices overseen by the Central, Eastern, Southern and Western Region Headquarters by the spring of 2015 β incorporate message tags within the main body of the product describing the source of the hazard report, damage potential, and if applicable, radar indications or physical observations of tornadoes or the possibility of a tornado; hazards are also summarized at the close of the product text (describing estimated maximum hail size and wind gusts, and if applicable, if a storm has the potential to produce a tornado or in the event of a tornado warning, the basis of the warning or its damage threat).<ref name=IBW>{{cite web|title=Impact Based Warnings|url=http://www.weather.gov/impacts/|website=National Weather Service|publisher=National Oceanic and Atmospheric Administration|access-date=March 12, 2014}}</ref><ref name="NWS Expirements">{{cite web |title=Enhanced Product β Tornado Warnings and Associated Follow-up Statements Modified to Emphasize Impacts, Intensity, and Recommended Actions via Bulleted Messages and Coded Tag Lines |url=http://products.weather.gov/PDD/PDD_CR_IBW_011012.pdf |url-status=dead |archive-url=https://web.archive.org/web/20120413081255/http://products.weather.gov/PDD/PDD_CR_IBW_011012.pdf |archive-date=April 13, 2012 |access-date=April 15, 2012 |website=National Weather Service |publisher=National Oceanic and Atmospheric Administration}}</ref><ref>{{cite news|author=y Jillian MacMath|date=April 5, 2012|title='CATASTROPHIC': Experimental Tornado Warnings to be Explicit|website=[[AccuWeather]]|publisher=AccuWeather Inc.|url=http://www.accuweather.com/en/weather-news/catastrophic-and-unsurvivable/63553|url-status=dead|access-date=May 26, 2017|archive-url=https://web.archive.org/web/20120404161254/http://www.accuweather.com/en/weather-news/catastrophic-and-unsurvivable/63553|archive-date=April 4, 2012}}</ref><ref>{{cite web|title=National Weather Service introduces impact-based warnings for tornadoes|url=https://www.earthmagazine.org/article/national-weather-service-introduces-impact-based-warnings-tornadoes|author=Nick Luchetti|periodical=Earth Magazine|publisher=[[American Geosciences Institute]]|date=April 15, 2013|access-date=May 26, 2017}}</ref> The wording "[[Particularly Dangerous Situation]]" (PDS), which originated by the Storm Prediction Center for use in tornado watch products during expected high-end severe weather outbreaks, is subjectively issued.<ref name="PDS">{{cite web|url=http://www.spc.noaa.gov/faq/#2.7|title=Storm Prediction Center Frequently Asked Questions (FAQ)|publisher=National Oceanic and Atmospheric Administration|date=April 18, 2004|access-date=May 26, 2017}}</ref> It is occasionally issued with tornado warnings, normally if a large tornado capable of producing EF3 to EF5 damage or staying on the ground for long-duration β sometimes uninterrupted β paths has been reported (although a [[tornado emergency]] may be issued in such cases if the tornado is expected to track into a densely populated area).<ref name="PDS"/> PDS warnings for other alerts occur with even less frequency, and their criteria varies depending on the alert type to which the wording is applied.<ref name="PDS"/> Until September 30, 2007, local offices of the National Weather Service issued warnings for severe thunderstorms, tornadoes, flash flooding and marine hazards using geopolitical boundaries. The implementation of storm-based warnings on October 1, 2007, saw alerts for these meteorological or hydrological threats be delineated by [[polygon]]al shapes in map-based weather hazard products, which outline the specified sections of government sub-jurisdictions that the warning covers, based on the projected path of a storm as determined by Doppler radar at the time of the warning's issuance; however, entire counties/parishes may sometimes be included in the warning polygon, especially if they encompass a small geographical area.<ref name="Storm-based">{{cite web|title=Storm-Based Warnings: Why Storm-Based Warnings?|url=http://www.weather.gov/sbwarnings/|website=NOAA Warning Decision Training Branch|publisher=National Oceanic and Atmospheric Administration|date=February 26, 2008|access-date=January 11, 2010|archive-url=https://web.archive.org/web/20100124141737/http://www.weather.gov/sbwarnings/|archive-date=January 24, 2010|url-status=dead}}</ref> Warnings can be expanded, contracted (by removing jurisdictions where SPC and NWS forecasters no longer consider there to be a viable threat of severe weather, in which case, the storm-based warning may take on a [[trapezoid]]al representation in map-based watch products) or canceled before their set time of expiration by local NWS offices. The NWS also releases Experimental Severe Weather Impact products for use on [[social media]] accounts maintained by local forecast offices as well as the Enhanced Data Display (EDD), an experimental pilot project created by the [[Charleston, West Virginia]] office's WeatherReady Nation initiative. The product provides a graphical depiction of short-fuse warnings and watches (specifically, tornado and severe thunderstorm watches and warnings, and flash flood warnings), showing a map of the warning area (outlined as a red polygon) and locations (including communities and interstate highways) that will be impacted. For severe thunderstorm, tornado and flash flood warnings, the estimated population count of the warned area and approximate totals of public schools and hospitals within the warning area as well as the maximum forecast intensity of hail size, wind gusts and potential tornadoes; tornado warnings referenced in the impact product also denote whether the warning was issued based on radar indication or ground confirmation.<ref>{{cite web|title=Experimental Severe Weather Impact Graphics|url=http://products.weather.gov/PDD/PDD-impact-graphics.pdf|publisher=National Weather Service|access-date=May 26, 2017|url-status=dead|archive-url=https://web.archive.org/web/20170208073235/https://products.weather.gov/PDD/PDD-impact-graphics.pdf|archive-date=February 8, 2017}}</ref>
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