Weather Forecast Offices that issue or have issued such warnings may use the same criteria meriting a PDS Severe Thunderstorm Warning to indicate life-threatening severe weather conditions that will impact a densely populated area. Severe weather statement (SVS) – A statement issued to provide updated information for active severe thunderstorm and tornado warnings to the public and emergency managers, with revised information including reports of observed severe weather and the approximate location of the storm cell (as indicated by the most recently updated NEXRAD data) at the time of the statement's issuance. Severe Weather Statements may include notices of cancellation (if the warning is being discontinued entirely, or if sections of counties or county-equivalent jurisdictions are being removed from the continuing warning), or notices of a warning being allowed to expire because the prompting storm has weakened below severe criteria. Flash flood watch (FFA; green box) – Conditions are favorable for flash flooding or urban flooding in and close to the watch area within the next 36 hours. These watches are issued by the Weather Forecast Office and are usually issued six to 24 hours in advance of expected flood potential. (The Heavy Rainfall Warning product issued by the Meteorological Service of Canada has a similar meaning as an NWS Flash Flood Watch.) Particularly dangerous situation flash flood watch (FFA) – Conditions are favorable for an extremely elevated level of severe and life-threatening flash flooding beyond the level of a normal flash flood watch in and close to the watch area. These watches are usually issued for a smaller area by the local WFOs than typical flash flood watches, which often span multiple county warning areas, and are usually valid for a longer period of time. This type of watch is usually only reserved for forecast "high-end" flash flood events. Flash flood warning (FFW) – Flash flooding—either indicated by Doppler weather radar or stream gauges, or reported by Skywarn spotters or local emergency officials—is occurring, imminent, or highly likely in the short term. A flash flood is a flood that occurs within six hours of excessive rainfall and poses a threat to life and/or property, especially in low-lying or flood prone areas (including urban areas with poor drainage, rivers and streams); ice jams and dam failures can also cause flash floods. These warnings are issued on a county by county (or equivalent thereof) basis by the local Weather Forecast Office