A winter storm warning ( SAME code: WSW) is a hazardous weather statement issued by Weather Forecast Offices (WFO) of the

National Weather Service The National Weather Service (NWS) is an Government agency, agency of the Federal government of the United States, United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weathe ...

(NWS) in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

to alert the public that a

winter storm A winter storm is an event in which wind coincides with varieties of precipitation that only occur at freezing temperatures, such as snow, mixed snow and rain, or freezing rain. In temperate continental climates, these storms are not necessar ...

is occurring or is about to occur in the area, usually within 36 hours of the storm's onset. A similar warning is issued by

Environment and Climate Change Canada Environment and Climate Change Canada (ECCC; french: Environnement et Changement climatique Canada),Environment and Climate Change Canada is the applied title under the Federal Identity Program; the legal title is Department of the Environment ...

(ECCC) through local forecast offices of the

Meteorological Service of Canada The Meteorological Service of Canada (MSC; french: Service météorologique du Canada – SMC) is a division of Environment and Climate Change Canada, which primarily provides public meteorological information and weather forecasts and warnings ...

Definition

Generally, a Winter Storm Warning is issued if the following criteria, at minimum, are forecast:

snow Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughout ...

accumulations usually between or greater than , or snow accumulations of usually or more with significant accumulation of

ice Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaq ...

( sleet or

freezing rain Freezing rain is rain maintained at temperatures below freezing by the ambient air mass that causes freezing on contact with surfaces. Unlike a mixture of rain and snow or ice pellets, freezing rain is made entirely of liquid droplets. The rain ...

). In the

Southern United States The Southern United States (sometimes Dixie, also referred to as the Southern States, the American South, the Southland, or simply the South) is a geographic and cultural region of the United States of America. It is between the Atlantic Ocean ...

, where severe winter weather is much less common and any snow is a more significant event, warning criteria are lower, as low as in the southernmost areas: as one goes from north to south, the accumulation estimates needed to meet warning criteria lessen. A warning can also be issued during high impact events of lesser amounts, usually early or very late in the season when trees have leaves and damage can result. Winter Storm Warnings for snow events are issued when winds are less than ; if the storm is expected to produce winds above this speed for at least three hours accompanying moderate to heavy snowfall, a

blizzard warning A blizzard warning ( SAME code: BZW) 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 gu ...

will be issued instead or as an upgrade to the winter storm warning. Usually, a large accumulation of ice alone with little to no snow will result in an

ice storm warning 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 ...

, or in the case of light freezing rain, a

winter weather advisory A winter weather advisory (originally identified as a Traveler's Advisory until the 2002-03 climatological winter when officially renamed, and informally as such by some local television stations thereafter) is a hazardous weather statement issued ...

, a

freezing rain advisory 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 (typically greater than ...

, or a freezing drizzle advisory. In lieu of issuing such a statement separately, Winter Storm Warnings can include verbiage indicative of a

wind chill advisory A wind chill advisory 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 wind chills are forecast to reach values low enough that it poses a ...

or a

wind chill warning 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 w ...

, if potentially life-threatening

wind chill Wind chill or windchill (popularly wind chill factor) is the lowering of body temperature due to the passing-flow of lower-temperature air. Wind chill numbers are always lower than the air temperature for values where the formula is valid. When ...

values (determined by local criteria) are forecast to accompany winter precipitation during the warning's duration. Beginning with the 2008–09 meteorological winter, the National Weather Service consolidated individual precipitation-specific bulletins for winter storms expected to create heavy snowfall (

heavy snow warning 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, th ...

), lake-effect snow (

lake effect snow warning A lake effect snow warning is a bulletin issued by the National Weather Service in the United States to warn of heavy snowfall accumulations that are imminent from convective snow generated by very cold airmass passing over unfrozen lakes (lake ef ...

) or sleet accumulations (sleet warning or heavy sleet warning) within the warned area, replacing them with variants of the Winter Storm Warning product outlining the accordant hazards being forecast: ; Winter storm warning for heavy snow : Replaced the heavy snow warning ; Winter storm warning for heavy wet snow : Same as above, except when the snow will also be wet ; Winter storm warning for heavy snow and blowing snow : When the criteria for both a WSW for heavy snow and a

for snow and blowing snow are met ear-blizzard conditions; Winter storm warning for heavy sleet : Replaced the sleet warning ; Winter storm warning for heavy snow and ice : When both the criteria for a WSW for heavy snow and an

are met ; Winter storm warning for snow and ice : When both the criteria for a winter weather advisory for snow and an ice storm warning are met ; Winter storm warning for sleet and freezing rain : When both the criteria for a winter weather advisory for sleet and an ice storm warning are met ; Winter storm warning for heavy lake-effect snow : Replaced the lake effect snow warning in some NWS county warning areas. (2017-2018 season) Additionally, all of the above warning types may also include verbiage indicative of a

wind advisory A wind advisory is generally issued by the National Weather Service of the United States when there are sustained thunderstorm winds of and/or gusts of over land. Winds over the said cap will trigger High wind warning, high wind alerts rather tha ...

to indicate strong winds that are expected to accompany the precipitation (e.g., "winter storm warning for heavy wet snow and strong winds"). The generic "''winter storm warning''" terminology may be used on its own, typically to indicate that all types of winter precipitation (as a mixture or in periods before transitioning between types) are expected in high amounts; however, it may be defined generically at the forecaster's discretion regardless of whether or not this condition is met.

Example of a winter storm warning

Source - U.S. NOAA National Weather Service


URGENT - WINTER WEATHER MESSAGE
National Weather Service Grand Rapids MI
331 PM EDT Fri Apr 13 2018

MIZ037>040-043>046-050>052-140345-
/O.NEW.KGRR.WS.W.0003.180414T0900Z-180415T1600Z/
Mason-Lake-Osceola-Clare-Oceana-Newaygo-Mecosta-Isabella-Muskegon-
Montcalm-Gratiot-
Including the cities of Ludington, Baldwin, Reed City, Clare, 
Hart, Fremont, Big Rapids, Mount Pleasant, Muskegon, Greenville, 
and Alma
331 PM EDT Fri Apr 13 2018

...WINTER STORM WARNING IN EFFECT FROM 5 AM SATURDAY TO NOON EDT
SUNDAY...

* WHAT...Heavy mixed precipitation expected. Total snow and sleet
  accumulations of two to four inches and ice accumulations of a
  quarter to half an inch are expected.

* WHERE...Portions of central and west central Michigan.

* WHEN...From 5 AM Saturday to noon EDT Sunday.

* ADDITIONAL DETAILS...Expect power outages and tree damage due 
  to the ice. Travel will be impossible. Tree branches could 
  fall. Expect significant reductions in visibility at times.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Winter Storm Warning means significant amounts of snow, sleet
and ice will make travel very hazardous or impossible. Strong
winds are also expected.


&&

$$

References

External links

National Weather Service

Federal Emergency Management Agency

Meteorological Service of Canada
{{SevWea nav Weather warnings and advisories

Definition

Example of a winter storm warning

See also

References

External links