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A severe thunderstorm warning is a severe weather warning product issued by regional offices of weather forecasting agencies throughout the world to alert the public that severe thunderstorms are imminent or occurring. A severe thunderstorm warning is issued when Doppler weather radar, trained storm spotters or local emergency management personnel indicate that a thunderstorm is producing large hail and high winds capable of causing significant damage, and is expected to continue producing severe weather along the storm's projected track. Flooding is also sometimes caused by torrential rainfall produced by a thunderstorm.
A small craft advisory is a type of wind warning issued by the National Weather Service in the United States. In Canada a similar warning is issued by Environment Canada. It is issued when winds have reached, or are expected to reach within 12 hours, a speed marginally less than gale force. A Small Craft Advisory may also be issued when sea or lake ice exists that could be hazardous to small boats.
A winter storm warning is a hazardous weather statement issued by Weather Forecast Offices (WFO) of the National Weather Service (NWS) in the United States to alert the public that a winter storm is occurring or is about to occur in the area, usually within 36 hours of the storm's onset.
A gale warning is an alert issued by national weather forecasting agencies around the world in an event that maritime locations currently or imminently experiencing winds of gale force on the Beaufort scale. Gale warnings allow mariners to take precautionary actions to ensure their safety at sea or to seek safe anchorage and ride out the storm on land. Though usually associated with deep low-pressure areas, winds strong enough to catalyze a gale warning can occur in other conditions too, including from anticyclones, or high-pressure systems, in the continental interior. The winds are not directly associated with a tropical cyclone.
A winter weather advisory is a hazardous weather statement issued by Weather Forecast Offices (WFO) of the National Weather Service in the United States when one or more types of winter precipitation—snow, rain and snow mixed, freezing rain, sleet, graupel, etc.—presenting a hazard, but not expected to produce accumulations meeting storm warning criteria, are forecast within 36 hours of the expected onset of precipitation or are occurring in the advisory's coverage area.
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.
A winter storm watch is issued by the National Weather Service of the United States when there is a possibility of heavy snow or potential of significant ice accumulations, without meeting a specific other winter criteria. The watch is typically issued 12 to 48 hours before the storm's expected arrival in the given area. The criteria for this watch can vary from place to place, which is true with other winter weather warning and advisories.
A heavy snow warning was a hazardous weather statement issued by the Weather Forecast Offices of the National Weather Service (NWS) in the United States which indicates a high rate of snowfall was occurring or was forecast to occur. Generally, the warning was issued for snowfall rates of 6 inches (15 cm) or more in 12 hours, or 8 inches (20 cm) or more in 24 hours.
At sea, a storm warning is a warning issued by the National Weather Service of the United States when winds between 48 knots and 63 knots are occurring or predicted to occur soon. The winds must not be associated with a tropical cyclone. If the winds are associated with a tropical cyclone, a tropical storm warning will be substituted for the storm warning and less severe gale warning.
A red flag warning is a forecast warning issued by the National Weather Service in the United States to inform the public, firefighters, and land management agencies that conditions are ideal for wildland fire combustion, and rapid spread. After drought conditions, when humidity is very low, and especially when there are high or erratic winds which may include lightning as a factor, the Red Flag Warning becomes a critical statement for firefighting agencies. These agencies often alter their staffing and equipment resources dramatically to accommodate the forecast risk. To the public, a Red Flag Warning means high fire danger with increased probability of a quickly spreading vegetation fire in the area within 24 hours.
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 blizzard warning is a hazardous weather statement issued by Weather Forecast Offices (WFO) of the National Weather Service (NWS) in the United States, which indicates heavy snowfall accompanied by sustained winds or frequent gusts of 35 mph (56 km/h) or greater are forecast to occur for a minimum of three hours. A blizzard tends to reduce visibilities to 1⁄4 mile (400 m) or less. A Severe Blizzard Warning is a variation issued in some cases of winds above 45 mph (72 km/h) and temperatures below 10 °F (−12 °C). Most local weather offices will activate and broadcast the SAME alarm tone on relevant NOAA Weather Radio stations for both varieties of warning. When the Wireless Emergency Alerts system was launched in 2012, blizzard warnings were initially sent as alerts to mobile phones; this practice was discontinued in November 2013.
A blizzard watch was a bulletin issued by the National Weather Service of the United States which meant winds greater than 35 miles per hour, mixed with falling or blowing snow, and visibilities of 1⁄4 mile (0.4 km) or less is forecast for a period of 3 hours or more. A blizzard watch was issued 12 to 48 hours before an expected blizzard event. As the forecast solidifies, a blizzard watch would be either downgraded to a winter storm warning or winter weather advisory for blowing snow or upgraded to a blizzard warning.
A Special Weather Statement is a form of weather advisory. Special Weather Statements are issued by the National Weather Service of the United States and the Meteorological Service of Canada. There are no set criteria for special weather statements in either country.
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 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 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 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.
A dust storm warning is issued by the National Weather Service in the United States when blowing dust is expected to frequently reduce visibility to 1⁄4 mile (400 m) or less, generally with winds of 25 miles per hour (40 km/h) or more.