and are generally in effect for two to six hours, although particularly during tropical cyclones a warning may last for a longer period of time, and occasionally last shorter than two hours. Particularly dangerous situation flash flood warning (FFW) – Issued within the initial flash flood warning or as a complete re-issuance of the previously issued warning, this indicates widespread, life-threatening flash flooding—caused by excessive rainfall, ice jams or imminent dam failures—has been indicated by Doppler weather radar, emergency personnel or trained observers over a broadly populated area. Flash flood emergency (FFS) – A flash flood emergency is a high-end usage of the flash flood warning. The flash flood emergency term is used when widespread flooding is occurring, and either, multiple water rescues have been reported in the past few hours, or if highly populated regions are undergoing significant flash flooding likely to cause loss of life and property. This terminology is more widely used during hurricanes with high amounts of moisture (an example is Hurricane Harvey in 2017, during which multiple flash flood emergencies were issued for portions of southeast Texas and southern Louisiana, including the Houston area). Flash flood statement (FFS) – A hydrological weather statement issued to provide updated information on active flash flood watches and warnings to the public and emergency managers. Deprecated Significant weather advisory (SPS; alt.: significant weather alert) – A strong thunderstorm below severe criteria, containing small hail below diameter, and/or strong winds of , is indicated by Doppler weather radar and may create some adverse impacts on travel. These advisories are issued as special weather statements written in the style of severe thunderstorm and other short-fused warnings, usually on a county by county (or equivalent thereof) basis. Some areas use an entirely different format (most notably WFOs in the Northeast and Mid-Atlantic), denoting which locations in each county will be affected by the thunderstorm. The NWS ceased use of the "significant weather advisory" titling in July 2021; special weather statements for non-severe thunderstorms concurrently adopted product language following the Impact Based Warning format used for severe convective storms. Winter precipitation Blizzard warning (BZW) – Sustained winds or frequent gusts of or greater, accompanying heavy snowfall, frequently reducing visibilities to or less is forecast to occur over a period of at least three hours. There are no temperature criteria in the definition of a blizzard, but freezing temperatures of at least and winds