Winter storm warning

A winter storm warning (SAME code: WSW) is a statement made by the National Weather Service of the United States which means a winter storm is occurring or is about to occur in the area, usually within 36 hours. Generally, a Winter Storm Warning is issued if the following criteria, at least, are forecast: usually between 4 inches (10 cm) to 7 inches (18 cm) or more of snow or usually 3 inches (7.6 cm) or more of snow with a large accumulation of ice. In the Southern United States, where severe winter weather is much less common and any snow is a more significant event, warning criteria are lower, as low as 1 inch (2.5 cm) in the southernmost areas: as one goes from north to south, the necessary accumulations 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 are issued when winds are less than 35mph; if the storm has winds above this wind speed, it becomes a blizzard warning.

Usually, a large accumulation of ice alone with little to no snow will result in an ice storm warning, or in the case of light freezing rain, a winter weather advisory, a freezing rain advisory, or drizzle advisory.

A similar warning is issued by Environment Canada's Meteorological Service of Canada from their offices.

Prior to the 2008–09 winter storm season, there was the heavy snow warning, specific for when only a heavy amount of snow was expected in the warned area. The Winter Storm Warning for Heavy Snow has since replaced it.

Types

Prior to the 2008-2009 winter weather season, there were several different bulletins which have since been consolidated into the Winter Storm Warning which now states which hazards it is being issued for.

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 winter weather advisory for snow and blowing snow are met [near-blizzard conditions][1]
Winter storm warning for heavy sleet
Replaced the sleet warning[2]
Winter storm warning for heavy snow and ice
When both the criteria for a WSW for heavy snow and an ice storm warning are met[3]
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 may also include "Strong Winds" in their title if strong winds are expected as well (e.g. winter storm warning for heavy wet snow and strong winds).

Also, the generic term, winter storm warning may be used on its own, typically to indicate that all three winter precipitation types are expected in high amounts; however, it may be used on its own as just a generic term at the forecaster's discretion regardless of whether or not this condition is met.

Example of a winter storm warning

[4]

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.


&&

$$

See also

Severe weather terminology (United States)

References
  1. "Winter Storm Warning In Effect". WDOR. 2014-01-14. Retrieved 2014-04-13.
  2. "Glossary - NOAA's National Weather Service". Weather.gov. 2009-06-25. Retrieved 2014-04-13.
  3. Daryl Herzmann Akrherz. "IEM :: Valid Time Extent Code (VTEC) App". Mesonet.agron.iastate.edu. Retrieved 2014-04-13.
  4. Source - U.S. NOAA National Weather Service
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