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A severe thunderstorm watch is a severe weather watch product issued by regional offices of weather forecasting agencies throughout the world when meteorological conditions are favorable for the development of severe thunderstorms as defined by regional criteria that may contain large hail, straight-line winds, lightning, intense hydrological phenomena and/or tornadoes. A severe thunderstorm watch does not necessarily mean that severe weather is actually occurring, only that conditions present a credible risk for thunderstorms producing severe weather phenomena to affect portions of the watch area. A watch must not be confused with a severe thunderstorm warning.
A blowing snow advisory was issued by the National Weather Service of the United States when wind driven snow reduces surface visibility and possibly hampers traveling. Blowing snow may be falling snow, or snow that has already accumulated but is picked up and blown by strong winds. This advisory was discontinued beginning with the 2008–09 winter storm season, replaced by the winter weather advisory for snow and blowing snow. However, if the storm is judged to be dangerous by local forecasters, a winter storm warning for heavy snow and blowing snow may be issued.
An ice storm warning is a hazardous weather statement issued by the Weather Forecast Offices of the National Weather Service in the United States which indicates that freezing rain produces a significant and possibly damaging accumulation of ice on surfaces. The criteria for this warning vary from state to state, but typically an ice storm warning will be issued any time more than 1⁄4 inch (6.4 mm) of ice at peak is expected to accumulate in an area, else a freezing rain or drizzle advisory is issued; in some areas, the criterion is 1⁄2 inch (13 mm) instead.
A flash flood warning is an hazardous weather statement issued by national weather forecasting agencies throughout the world to alert the public that a flash flood is imminent or occurring in the warned area. A flash flood is a sudden, violent flood after a heavy rain, or occasionally after a dam break. Rainfall intensity and duration, topography, soil conditions, and ground cover contribute to flash flooding.
An excessive heat warning is a notice issued by the National Weather Service of the United States within 12 hours of the heat index reaching one of two criteria levels. In most areas, a warning will be issued if there is a heat index of at least 105 °F (41 °C) for more than three hours per day for two consecutive days, or if the heat index is greater than 115 °F (46 °C) for any period of time.
A particularly dangerous situation (PDS) tag is enhanced wording first used by the Storm Prediction Center (SPC), a national guidance center of the United States National Weather Service, for tornado watches and eventually expanded to use for other severe weather watches and warnings by local NWS forecast offices. It is issued at the discretion of the forecaster composing the watch or warning and implies that there is an enhanced risk of very severe and life-threatening weather, usually a major tornado outbreak or a long-lived, extreme derecho event, but possibly another weather hazard such as an exceptional flash flood or wildfire.
A flash flood watch is issued by the National Weather Service 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.
A freezing rain advisory was an advisory issued by the National Weather Service in the United States when freezing rain or freezing drizzle was expected to cause significant inconveniences, but did not meet warning criteria.
A lake wind advisory is issued by the United States National Weather Service local forecast offices when windy conditions on area lakes are expected to be hazardous for boaters and other recreational events on or around lakes.
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."
A river flood watch is issued by the National Weather Service of the United States when flooding at formal forecast points with river gaging sites and established flood stages is possible. Flooding may be caused by various reasons, such as heavy rain in the vicinity of the river, melting snow, and/or ice jams.
A river flood advisory is issued by the National Weather Service of the United States when minor flooding at formal forecast points with river gaging sites and established flood stages is possible. Flooding may have many causes, such as heavy rain in the vicinity of the river, melting snow or ice jams.
A wind chill watch is issued by the National Weather Service of the United States when the wind chill could reach dangerous levels within the next 12 to 48 hours. The exact definition required to issue a watch varies from state to state or from National Weather Service county warning areas to another, but if forecasters believe conditions are favorable for life-threatening wind chills meeting local criteria, a watch will be issued. People going outside should plan to protect themselves against hypothermia and frostbite.
A wind chill warning is a hazardous weather statement issued by local forecast offices of the National Weather Service (NWS) in the United States and previously by the Meteorological Service of Environment and Climate Change Canada (ECCC) when wind chills are forecast to reach values low enough for residents and travelers to be susceptible to life-threatening medical conditions or death associated with accelerated body heat loss.
A gale watch is issued by the National Weather Service of the United States when there is an increased risk for a gale-force wind event, meaning sustained surface winds, or frequent gusts, of 34 to 47 knots, but the occurrence, location, and/or timing of the event is still uncertain.
A Hazardous Seas Warning is issued by the National Weather Service of the United States when wave heights and/or wave steepness values reach certain criteria. These criteria are defined by the local forecast office. Such tall waves can pose a serious threat to vessels that do not seek shelter.
A Hazardous Seas Watch is issued by the National Weather Service of the United States when there is an increased threat of high wave heights and/or wave steepness values reach a certain criteria, but the occurrence, timing, and/or location are still uncertain, though the area of concern is known. The criteria are set by the local forecast offices. It is normally accompanied with strong winds, and occasionally even cyclonic activity. Such tall waves can pose a serious threat to vessels that do not seek shelter, as well as vehicles and property very close to concerned waters.
A Heavy Freezing Spray Warning is issued by the National Weather Service of the United States to warn vessels that rapid accumulation and icing of freezing water droplets due to a combination of cold water, wind, cold air, and vessel or vehicle movement is likely. Accumulation rates of 2 cm per hour or greater must be possible for a warning to be issued, or else a freezing spray advisory would be issued.
A wind advisory is generally issued by the National Weather Service of the United States when there are sustained non-thunderstorm winds of 31–39 miles per hour (50–63 km/h) and/or gusts of 46–57 miles per hour (74–92 km/h) over land. Winds over the said cap will trigger high wind alerts rather than a wind advisory. The advisory is site specific, but winds of this magnitude occurring over an area that frequently experiences such wind speeds on a basis will not trigger a wind advisory. A slightly lower wind speed in areas around lakes may trigger a Lake wind advisory instead.