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. (Thus, as you go from south to north the necessary accumulations get higher.) 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]

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 ice storm warning 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 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

URGENT - WINTER WEATHER MESSAGE
National Weather Service Grand Rapids MI
324 AM EDT Thu Apr 12 2018

MIZ037>040-043>046-121530-
/O.NEW.KGRR.WS.A.0002.180414T0900Z-180415T1600Z/
Mason-Lake-Osceola-Clare-Oceana-Newaygo-Mecosta-Isabella-
Including the cities of Ludington, Baldwin, Reed City, Clare, 
Hart, Fremont, Big Rapids, and Mount Pleasant
324 AM EDT Thu Apr 12 2018

...WINTER STORM WATCH IN EFFECT FROM LATE FRIDAY NIGHT THROUGH
SUNDAY MORNING...

* WHAT...Heavy mixed precipitation possible. Total snow and sleet
  accumulations of up to one inch and ice accumulations of one
  quarter to three quarters of an inch are possible. Wind gusts
  over 30 mph from the northeast will increase the potential
  impacts.

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

* WHEN...From late Friday night through Sunday morning.

* ADDITIONAL DETAILS...Expect power outages and tree damage due 
  to the ice. Travel could be impossible. Significant reductions 
  in visibility are possible.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Winter Storm Watch means there is potential for significant
snow, sleet or ice accumulations that may impact travel. Continue
to monitor the latest forecasts.

&&

$$

See also

Severe weather terminology (United States)

External links

• National Weather Service
• Federal Emergency Management Agency
• Meteorological Service of Canada