Lake-effect snow is produced during cooler atmospheric conditions when a cold air mass moves across long expanses of warmer lake water. The lower layer of air, heated up by the lake water, picks up water vapor from the lake and rises up through the colder air above. The vapor then freezes and is deposited on the leeward (downwind) shores.
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 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 lake effect snow advisory was issued by the National Weather Service of the United States when lake effect snow may pose a hazard or is life-threatening. The snow must be completely caused by a convective snow development over a lake and not by a low pressure system. The criteria for this advisory vary from area to area.
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 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.
A snowsquall, or snow squall, is a sudden moderately heavy snowfall with blowing snow and strong, gusty surface winds. It is often referred to as a whiteout and is similar to a blizzard but is localized in time or in location and snow accumulations may or may not be significant.
The October 2006 Buffalo storm was an unusual early-season lake effect snow storm that hit the Buffalo, New York area and other surrounding areas of the United States and Canada, from the afternoon of Thursday, October 12 through the morning of Friday, October 13, 2006. It was called Lake Storm Aphid by the National Weather Service office in Buffalo, in accordance with their naming scheme for lake-effect snowstorms for that year, which related to insects, though locals never used that terminology and have simply referred to it as the October Surprise or the October Storm or Arborgeddon. The October Surprise was most recently documented in a collection of narratives, historical and meteorological insight, and the adventures of the local NFL team, the Buffalo Bills, as they had to travel to Detroit in spite of the destruction from the storm, entitled Thunder Snow of Buffalo.
A snow squall warning is a bulletin issued by Environment Canada's Meteorological Service of Canada and the National Weather Service in the United States to warn population of two types of snow events reducing visibility in blowing snow: lake effectsnow squalls and frontal snow squalls.
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 lake effect snow watch was a bulletin issued by the National Weather Service in the United States to warn of heavy snowfall amounts that will be possible from convective snow generated by cold air masses passing over unfrozen lakes. The criteria for amounts may vary over different county warning areas.
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 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 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.
The December 15–17, 2020 nor'easter was a powerful nor'easter that hammered the Northeastern United States and produced widespread swaths of over 1 foot (12 in) of snow in much of the region from December 15–17, 2020, ending a 1,000+ day high-impact snowstorm drought in much of the Mid-Atlantic and coastal New England regions. The system developed out of a weak area of low-pressure that first developed over the Central United States producing some snowfall before moving eastward, and by December 16, a new, dominant area of low pressure began to develop along the Southeast coast. This low steadily deepened as it moved along and impacted the Mid-Atlantic coastline, prompting several winter-related advisories and warnings for much of the Northeast.
