Shelter in place warning (SPW) – Indicates an event (such as the release of hazardous materials containing toxic fumes or radioactivity harmful to residents in the warning area) in which the public is recommended to shelter in place and take necessary safety precautions. Tsunami watch (TSA) – A tsunami is forecast to impact the specified area. Tsunami warning (TSW) – A tsunami with the potential of causing widespread coastal flooding accompanied by powerful currents and inundation and/or significant damage to adjacent property is imminent, expected or occurring and may continue for several hours after the wave's initial arrival, issued by the National Tsunami Warning Center. Tsunami advisory – A tsunami with the potential to generate strong currents or waves dangerous to those in or very near the water is imminent, expected, or occurring. The threat may continue for several hours after initial arrival, but significant inundation of land and adjacent property is not expected. Volcano warning (VOW) – Indicates volcanic activity that is ongoing or imminent. Wind and tropical cyclones Wind alerting is classified into groups of two Beaufort numbers, beginning at 6–7 for the lowest class of wind advisories. The last group includes three Beaufort numbers, 14–16. The actual alerts can be categorized into three classes: maritime wind warnings, land wind warnings, and tropical cyclone warnings. Advisory-force and gale-force winds will not trigger a separate wind advisory or warning if a Blizzard warning is already in effect. However, as seen with Hurricane Sandy, if widespread high wind warnings are in effect prior to the issuance of a blizzard warning, the high wind warnings may be continued. Wind alert terms and signals * † ‡ Hazardous weather risks The various weather conditions described above have different levels of risk. The National Weather Service uses a multi-tier system of weather statements to notify the public of threatening weather conditions. These statements are used in conjunction with specific weather phenomena to convey different levels of risk. In order of increasing risk, these statements are: Outlook – A Hazardous Weather Outlook is issued daily to indicate that a hazardous weather or hydrologic event may occur in the next seven days. Each segment of the product will contain sections outlining hazardous weather in the short term (through Day 1) and long term (for Days 2-7), and spotter information. The outlook will include information about potential severe thunderstorms, heavy rain or flooding, winter weather, extremes