View source for Winter storm

{{Short description| Weather of freezing precipitation and high winds}}
{{About|storms in winter|other uses|Winter storm (disambiguation)}}
{{Redirect|Snowstorm}}
[[File:Winter Storm Jonas 2016 NYC Pershing Square.jpg|thumb|250px|Heavy snowfall and strong winds during [[January 2016 United States blizzard|a 2016 blizzard]] in [[New York City]].]]
{{Weather}}
[[File:West Virginia National Guard members conduct road clearing and debris removal operations.jpg|thumb|upright|[[West Virginia National Guard|National Guard]] members clear a road of fallen trees after a [[February 15–20, 2021 North American winter storm|February 2021 winter storm]] in [[Putnam County, West Virginia|Putnam County]], [[West Virginia]].]]
A '''winter storm''' (also known as '''snow storm''') is an event in which wind coincides with varieties of [[precipitation]] that only occur at [[freezing]] [[temperature]]s, such as [[snow]], [[Rain and snow mixed|mixed snow and rain]], or [[freezing rain]]. In [[Continental climate|temperate continental and subarctic]] [[climate]]s, these storms are not necessarily restricted to the winter season, but may occur in the late autumn and early spring as well. A snowstorm with strong winds and low visibility is called a [[blizzard]].

== Formation ==
{{Globalize section|United States|date=November 2024}}

Winter storms are formed when moist air rises up into the [[atmosphere]], creating [[Low-pressure area|low pressure]] near the ground and clouds up in the air. The air can also be pushed upwards by hills or large mountains. The upward motion is called [[Lift (force)|lift]].<ref name="NSSL1">{{cite web |last= [[National Severe Storms Laboratory]] |title=Severe Weather 101: Winter Weather Basics |url=https://www.nssl.noaa.gov/education/svrwx101/winter/ |publisher=[[National Oceanic and Atmospheric Administration]] |access-date=19 February 2021}}</ref> The moisture is collected by the wind from large bodies of water, such as a big lake or the ocean. If temperature is below [[freezing]], {{convert|0|C}}, near the ground and up in the clouds, [[precipitation]] will fall as snow, ice, [[rain and snow mixed]] (sleet), [[ice pellets]] or even [[graupel]] (soft hail).<ref name="NSSL1" /><ref name="NSSL2">{{cite web |last= [[National Severe Storms Laboratory]] |title=Severe Weather 101: Hail Types - How does hail compare to other types of frozen precipitation? |url=https://www.nssl.noaa.gov/education/svrwx101/hail/types/ |publisher=[[National Oceanic and Atmospheric Administration]] |access-date=19 February 2021}}</ref> Since cold air can not hold as much moisture as warm air, the total precipitation will be less than at higher temperature.<ref name="UCAR">{{cite web |title=Winter Storms |url=https://scied.ucar.edu/learning-zone/storms/winter-storms |website=Center for Science Education |publisher=[[University Corporation for Atmospheric Research]] |date=2019 |access-date=19 February 2021}}</ref>

Winter storm warnings will be issued if:
* Snow accumulation is {{convert|6|in|cm|abbr=on}} or more in 12 hours, or {{convert|8|in|cm|abbr=on}} or more in 24 hours.<ref name="topics">{{cite web |title=Central Illinois - Winter Weather Topics |url=https://www.weather.gov/ilx/swop-wintertopics4 |website=National Weather Service |publisher=[[National Oceanic and Atmospheric Administration]] |access-date=19 February 2021}}</ref>
* Blowing snow is reducing visibility in large areas at winds less than {{convert|35|mph|m/s|abbr=on}}.<ref name="warning" />
* Ice accumulations on surfaces are {{convert|0.25|in|cm|abbr=on}} or more.<ref name="topics" />
* Ice pellets larger than {{convert|1|in|cm|abbr=on}} are formed.<ref name="warning">{{cite web |title=Caribou, ME - Warning Criteria |url=https://www.weather.gov/car/Warning_Criteria |website=National Weather Service |publisher=[[National Oceanic and Atmospheric Administration]] |access-date=19 February 2021}}</ref>
* [[Wind chill]] index is less than {{convert|-35|F|C|abbr=on}} for more than 3 hours and sustained [[wind speed]] of at least {{convert|10|mph|m/s|abbr=on}}.<ref name="warning" />
Snowstorms with wind speed of more than {{convert|35|mph|m/s|abbr=on}} and reduced visibility of less than {{convert|0.25|mi|m}} for 3 hours or longer are called [[blizzard]]s.<ref name="warning" /><ref name="topics" />

=== Terminology ===
Severe winter weather conditions called "winter storms", can be local weather fulfilling the criteria for 24 hours, or large [[storm system]]s covering part of a continent for several days. With large, massive winter storms, weather in any part of the area covered by the extreme weather is usually called "storm"; even if meteorological criteria for winter storms are not met everywhere.<ref name="guardian1">{{cite web |last1=Salam |first1=Erum |title=Millions without power and 21 dead as ferocious winter weather sweeps US |url=https://www.theguardian.com/us-news/2021/feb/16/texas-weather-snow-storm-latest-news-power-outages-deaths |website=[[The Guardian]] |access-date=19 February 2021 |date=17 February 2021}}</ref> An example of this is the [[February 13–17, 2021 North American winter storm]] with snowfall and below freezing temperatures as far south as [[Texas]] and the Gulf of Mexico.<ref name="time">{{cite magazine |last1=Sullivan |first1=Brian K. |last2=Malik |first2=Naureen S. |title=5 Million Americans Have Lost Power From Texas to North Dakota After Devastating Winter Storm |url=https://time.com/5939633/texas-power-outage-blackouts/#:~:text=5%20Million%20Americans%20Have%20Lost,on%20Feb.%2015%2C%202021. |magazine=[[Time (magazine)|Time]] |access-date=19 February 2021 |date=15 February 2021}}</ref><ref name="guardian1" />

== Snowstorm ==
[[File:Snowy Kajaaninkatu Oulu 2008 03 22.JPG|thumb|left|Snowstorm in [[Oulu]], Finland]]
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| image1            = Fullerton harbor looking south Chicago Feb 2 2011 storm.JPG
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| image2            = Chicago at Dusk in December.JPG
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| footer            = [[Chicago]]'s Fullerton Harbor looking south during the [[2011 Groundhog Day blizzard|January 31 – February 2, 2011, North American winter storm]] (left) and on a clear day for comparison.
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Snowstorms are storms where large quantities of [[snow]] fall. {{convert|2|in|cm|abbr=on}} of snow is enough to create serious disruptions to [[traffic]] and school transport (because of the difficulty to drive and manoeuvre the school buses on slick roads). This is particularly true in places where snowfall is not typical but heavy accumulating snowfalls can occur. In places where snowfall is typical, such small snowfalls are rarely disruptive, because of effective snow and ice removal by municipalities, increased use of [[four-wheel drive]] and [[snow tire]]s, and drivers being more used to winter conditions. Snowfalls in excess of {{convert|6|in|cm|abbr=on}} are usually universally disruptive.

A large number of severe snowstorms, some of which were blizzards, occurred in the United States during [[Great Blizzard of 1888|1888]] and [[North American blizzard of 1947|1947]] as well as the early and mid-1990s. The snowfall of 1947 exceeded {{convert|2|ft|cm|abbr=on}} with drifts and snow piles from plowing that reached {{convert|12|ft|m|abbr=on}} and for months as temperatures did not rise high enough to melt the snow. The [[1993 Storm of the Century|1993 "Superstorm"]] manifested as a blizzard in most of the affected areas.

Severe snowstorms could be quite dangerous: a {{convert|6|in|cm|abbr=on}} snow depth will make some unplowed roads impassable, and it is possible for cars to get stuck in the snow. Snow depth exceeding {{convert|12|in|cm|abbr=on}} especially in southern or generally warm climates will cave the roofs of some homes and cause loss of electricity. Standing dead trees can also be brought down by the weight of the snow, especially if it is wet. Even a few inches of dry snow can form drifts many feet high under windy conditions.

=== Hazards from snowfall ===
[[File:Nevicata eccezionale (4433552880).jpg|thumb|Snow storm in [[Modena]], Italy]]
Accumulated snow can make driving motor vehicles very hazardous. Snow on roadways reduces friction between tires and the road surface, which in turn lowers the maneuverability of a vehicle considerably. As a result, average driving speeds on public roads and highways are reduced by up to 40% while heavy snow is falling.<ref>{{Cite web | url=https://ops.fhwa.dot.gov/weather/weather_events/snow_ice.htm | title=Snow & Ice – FHWA Road Weather Management}}</ref> Visibility is reduced by falling snow, and this is further exacerbated by strong winds which are commonly associated with winter storms producing heavy snowfall. In [[Blizzard|extreme cases]], this may lead to prolonged [[whiteout (weather)|whiteout]] conditions in which visibility is reduced to only a few feet due to falling or blowing snow. These hazards can manifest even after snowfall has ended when strong winds are present, as these winds will pick up and transport fallen snow back onto roadways and reduce visibility in the process. This can even result in [[Ground blizzard|blizzard conditions]] if winds are strong enough.<ref>{{Cite web|url=https://www.weather.gov/mkx/wwa-impacts|title=Winter Weather Awareness – Impacts On Society|first=NOAA|last=US Department of Commerce|website=www.weather.gov}}</ref> Heavy snowfall can immobilize a vehicle entirely, which may be deadly depending on how long it takes rescue crews to arrive. The clogging of a vehicle's tailpipe by snow may lead to [[carbon monoxide]] buildup inside the cabin.<ref>{{Cite web|url=https://www.weather.gov/dmx/wintersafety|title=Winter Weather Safety|first=NOAA|last=US Department of Commerce|website=www.weather.gov}}</ref>

[[File:RFA Tidespring during bad weather off the UK coast MOD 45163864.jpg|thumb|left|Wet snow and sleet during a winter storm, on the deck of [[Royal Fleet Auxiliary|RFA]] ''[[RFA Tidespring (A136)|Tidespring]]'' south of [[Plymouth]] in the English Channel.]]
Depending on the temperature profile in the atmosphere, snow can be either ''wet'' or ''dry''. Dry snow, being lighter, is transported by wind more easily and accumulates more efficiently. Wet snow is heavier due to the increased water content. Significant accumulations of heavy wet snow can cause roof damage. It also requires considerably more energy to move and this can create health problems while shoveling when combined with the harsh weather conditions. Numerous deaths as a result of heart attacks can be attributed to snow removal.<ref>{{Cite news | url=https://www.bbc.com/news/blogs-magazine-monitor-30119410 | title=Why do so many people die shovelling snow?| work=BBC News| date=2017-02-09| last1=Why| first1=Who}}</ref> Accretion of wet snow to elevated surfaces occurs when snow is "sticky" enough which can cause extensive tree and power line damage in a manner similar to ice accretion during ice storms. Power can be lost for days during a major winter storm, and this usually means the loss of heating inside buildings. Other than the obvious risk of hypothermia due to cold exposure, another deadly element associated with snowstorms is [[carbon monoxide poisoning]] which can happen anytime combustion products from generators or heating appliances are not properly vented. Partially or fully melted snow on roadways can refreeze when temperatures fall, creating [[black ice]].

== Freezing rain ==
{{Main|Ice storm|Freezing rain}}

[[File:IceStormPowerLines.png|thumb|Coated in ice, power and telephone lines sag and often break, resulting in power outages.]]
[[File:Frozen rain covering hawthorn berries.jpg|thumb|[[Crataegus|Hawthorn]] berries covered in icy glaze due to freezing rain. Ice storms often coat many surfaces. Severe ice storms, which may occur in spring, can kill plant life.]]
Heavy showers of [[freezing rain]] are one of the most dangerous types of winter storm. They typically occur when a layer of warm air hovers over a region, but the ambient temperature a few meters above the ground is near or below {{convert|0|°C|°F|abbr=on}}, and the ground temperature is sub-freezing.

While a {{convert|10|cm|in|abbr=on}} snowfall is somewhat manageable by the standards of the northern United States and Canada, a comparable {{convert|10|mm|in|2|abbr=on}} precipitation of an ice storm can paralyze a region; driving becomes extremely hazardous, telephone and [[Electric power transmission|power lines]] are damaged, and crops may be ruined.<ref>{{Cite journal|url=http://www.ncdc.noaa.gov/billions/docs/smith-and-katz-2013.pdf|last1=Smith|first1=A.B.|first2=R.|last2=Katz|date=2013|title=U.S. Billion-dollar Weather and Climate Disasters: Data sources, Trends, Accuracy and Biases|journal=Natural Hazards|volume=67|issue=2 |pages=387–410|doi=10.1007/s11069-013-0566-5|bibcode=2013NatHa..67..387S |s2cid=30742858|archive-url=https://web.archive.org/web/20140925050418/http://www.ncdc.noaa.gov/billions/docs/smith-and-katz-2013.pdf|archive-date=25 September 2014|url-status=dead}}</ref>

=== Notable ice storms ===
Notable ice storms include an [[El Niño]]-related [[January 1998 North American ice storm|North American ice storm of 1998]] that affected much of eastern Canada, including [[Montreal]] and [[Ottawa]], as well as upstate [[New York (state)|New York]] and parts of upper [[New England]]. Three million people lost power, some for as long as six weeks. One-third of the trees in Montreal's [[Mount Royal]] park were damaged, as well as a large proportion of the [[sugar]]-producing [[maple]] trees. The amount of economic damage caused by the storm has been estimated at $3 billion [[Canadian dollar|CAD]].

* 2000 Christmas Day Ice Storm, caused devastating electrical issues in parts of [[Arkansas]], [[Oklahoma]], and [[Texas]]. The city of [[Texarkana, Arkansas]] experienced the worst damage, at one point losing the ability to use telephones, electricity and running water. In some areas in Arkansas, Oklahoma, Texas and eventually [[Louisiana]], over {{convert|1|in|mm|abbr=on}} of ice accumulated from the freezing rain.<ref>{{Cite web|url=http://www.srh.noaa.gov/shv/?n=ice2000|title=Ice Storm December 25-26, 2000|date=31 July 2009|website=National Weather Service Weather Forecast Office|publisher=National Oceanic and Atmospheric Administration|access-date=26 April 2016}}</ref><ref>{{Cite web|url=https://www.wunderground.com/news/top-10-worst-ice-storms-20131205?pageno=4|title=The Nation's 10 Worst Ice Storms|last1=Dolce|first1=Chris|last2=Erdman|first2=Jon|date=12 February 2014|website=Weather Underground|access-date=26 April 2016}}</ref>
* [[North Carolina ice storm of 2002|2002 North Carolina ice storm]], resulted in massive power loss throughout much of the state, and property damage due to falling trees. Except in the mountainous western part of the state, heavy snow and icy conditions are rare in [[North Carolina]].
* [[December 2005 North American ice storm|2005 December Ice Storm]], was another severe winter storm producing extensive ice damage across a large portion of the Southern United States on December 14 to 16. It led to [[power outage]]s and at least 7 deaths.
* 2005 January winter storm in [[Kansas]], had been declared a major disaster zone by President [[George W. Bush]] after an ice storm caused nearly $39 million in damages to thirty-two counties. Federal funds were provided to the counties during January 4–6, 2005 to aid the recovery process.<ref>{{cite web|url=http://www.accesskansas.org/ksadjutantgeneral/News%20Releases/2005/Gov%2002-09-05.htm|title=Presidential Disaster Declaration authorized for Kansas counties hit by January ice storm|website=accesskansas.org|access-date=8 April 2016|url-status=dead|archive-url=https://web.archive.org/web/20160425095129/http://www.accesskansas.org/ksadjutantgeneral/News%20Releases/2005/Gov%2002-09-05.htm|archive-date=25 April 2016}}</ref>
* [[January 2009 North American ice storm|2009 January Central Plains and Midwest ice storm]], was a crippling and historic ice storm. Most places struck by the storm, saw {{convert|2|in|mm}} or more of ice accumulation, and a few inches of snow on top of it. This brought down power lines, causing some people to go without electricity for a few days, to a few weeks. In some cases, electricity was out for a month or more. At the height of the storm, more than 2 million people were without electricity.
*[[February 13-17, 2021 North American winter storm|2021 Winter Storm]] was the deadliest winter storm since the [[Blizzard of 1996]] impacting most of the midwest and southcentral United States. The state of Texas gained notable publicity due to the failure of the state's power grid, causing blackouts and power outages for 7–10 days across the state.

== Preparing for winter storms ==
[[File:2008 China storms Anhui 6.JPG|thumb|[[2008 Chinese winter storms|2008 Chinese winter storm]] in [[Hefei]], [[Anhui]] Province, China]]
In countries where winter storms can occur, governments and health organizations have websites and online services with advice about how to prepare for the consequences of severe weather. Advices vary with housing standards, [[infrastructure]] and safety regulations, but some tips are the same, such as: stock up on three days of food, water, medicines and [[Personal care|hygiene items]], keep warm clothes ready, keep a [[flashlight]] and extra batteries, stay informed, help each other, do not travel unless absolutely necessary.<ref name="met">{{cite web |title=10 things you should do now to prepare for winter |url=https://www.metoffice.gov.uk/weather/warnings-and-advice/seasonal-advice/10-things-you-should-do-now-to-prepare-for-winter |website=www.metoffice.gov.uk |publisher=[[Met Office]] |access-date=19 February 2021}}</ref><ref>{{cite web |title=Winter Storm Safety |url=https://www.redcross.org/get-help/how-to-prepare-for-emergencies/types-of-emergencies/winter-storm.html |website=www.redcross.org |publisher=[[American Red Cross]] |access-date=19 February 2021}}</ref><ref name="msb">{{cite web |title=If crisis or war comes |url=https://rib.msb.se/filer/pdf/28706.pdf |website=www.msb.se |publisher=[[Swedish Civil Contingencies Agency]] |access-date=19 February 2021 |date=2018 |archive-url=https://web.archive.org/web/20191014161937/https://rib.msb.se/filer/pdf/28706.pdf |archive-date=14 October 2019 |url-status=live }}</ref><ref name="mass">{{cite web |title=Winter Storm Safety Tips |url=https://www.mass.gov/info-details/winter-storm-safety-tips |website=www.mass.gov |publisher=[[Massachusetts|Commonwealth of Massachusetts]] |access-date=19 February 2021}}</ref>

== See also ==
{{div col|colwidth=28em}}
* [[Alpine storms]]
* [[Classifications of snow]]
* [[Cold wave]]
* [[Heavy snow warning]]
* [[Ice storm warning]]
* [[List of snowiest places in the United States by state]]
* [[Severe weather terminology (United States)]]
* [[Severe weather terminology (Canada)]]
* [[Siberian Express]]
* [[Snow emergency]]
* [[Winter weather advisory]]
* [[Winter storm warning]]
* [[Winter storm watch]]
* [[Blizzard]]s and other storms
**[[Great Blizzard of 1888]]
** [[North American blizzard of 1947]]
** [[2011 Groundhog Day blizzard]]
** [[July 2007 Argentine winter storm]]
** [[October 2013 North American storm complex]]
** [[St. Patrick's Day Snowstorm]] of 1892
** [[Winter of 2010–11 in Europe]]
** [[Winter of 2010–11 in Great Britain and Ireland]]
** [[Late December 2022 North American winter storm]]
{{div col end}}

== References ==
{{Wikivoyage|Travelling in cold weather}}

* {{Cite web |title=Billion-Dollar Weather and Climate Disasters |url=http://www.ncdc.noaa.gov/billions |website=NCEI}}
* ''Weather For Dummies'', by John D. Cox
{{Reflist}}

{{Natural disasters}}
{{Authority control}}

[[Category:Snow or ice weather phenomena]]
[[Category:Storm]]
[[Category:Weather hazards]]
[[Category:Winter phenomena|Storm]]