Editing Heat wave (section)

=== Definitions by country ===
==== Europe ====
Denmark defines a national heat wave (''hedebølge'') as a period of at least 3 consecutive days in which the average maximum temperature across more than half the country exceeds {{convert|28|°C|°F|1}}. The [[Danish Meteorological Institute]] also has a definition for a "warmth wave" (''varmebølge''). It defines this using the same criteria for a {{convert|25|°C|°F|1}} temperature.<ref>{{cite web|url=http://www.dmi.dk/dmi/danmark_faar_varme-_og_hedeboelge |title=Danmark får varme- og hedebølge |language=da |publisher=Danish Meteorological Institute |date=22 July 2008 |access-date=18 July 2013 |url-status=dead |archive-url=https://web.archive.org/web/20080723170544/http://www.dmi.dk/dmi/danmark_faar_varme-_og_hedeboelge |archive-date=23 July 2008 }}</ref> Sweden defines a heat wave as at least five days in a row with a daily high exceeding {{convert|25|°C|°F|1}}.<ref>{{cite web|url=http://www.smhi.se/kunskapsbanken/klimat/varmebolja-1.22372 |title=Värmebölja Klimat: Kunskapsbanken SMHI |language=sv |publisher=Smhi.se |access-date=17 July 2013}}</ref>

In Greece, the [http://www.hnms.gr/emy/el/ Hellenic National Meteorological Service] defines a heat wave as occurring over three consecutive days with temperatures at 39&nbsp;°C (102&nbsp;°F) or higher. In the same period the minimum temperature is {{convert|26|°C|°F}} or more. During this period, there are either no winds or only weak winds. These conditions occur in a broad area.

The Netherlands defines a heat wave as a period of at least five consecutive days in which the maximum temperature in [[De Bilt]] exceeds {{convert|25|°C|°F}}. During this period the maximum temperature in De Bilt must exceed {{convert|30|°C|°F}} for at least three days. Belgium also uses this definition of a heat wave with [[Ukkel]] as a reference point. So does Luxembourg.

In the United Kingdom, the [[Met Office]] operates a Heat Health Watch system. This places each Local Authority region into one of four levels. Heat wave conditions occur when the maximum daytime temperature and minimum nighttime temperature rise above the threshold for a particular region. The length of time above that threshold determines the level. Level 1 represents normal summer conditions. Level 2 occurs when there is a 60% or higher risk that the temperature will be above the threshold levels for two days and the intervening night. Level 3 arises when the temperature has been above the threshold for the preceding day and night, and there is a 90% or higher chance that it will stay above the threshold in the following day. Level 4 is triggered if conditions are more severe than those of the preceding three levels. Each of the first three levels gives rise to a particular state of readiness and response by the social and health services. Level 4 involves a more widespread response.<ref>{{cite web |date=31 August 2011 |title=Heat-health watch |url=http://www.metoffice.gov.uk/public/weather/heat-health/ |access-date=17 July 2013 |publisher=Met Office}}</ref> The threshold for a heat wave occurs when there are at least three days above {{convert|25|°C|°F}} across much of the country. Greater London has a threshold of {{convert|28|°C|°F}}.<ref>{{cite web |date=26 May 2023 |title=What is a heatwave?|url=https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/temperature/heatwave |access-date=26 May 2023 |publisher=Met Office}}</ref>

In Ireland, a heat wave is defined as temperatures exceeding {{convert|25|°C|°F}} for five or more consecutive days.<ref>{{cite web |date=2 Jun 2023 |title=Summer Centre|url=https://www.met.ie/climate/summer-centre |access-date=1 Feb 2025 |publisher=Met Éireann}}</ref>

==== North America ====
In the United States, definitions also vary by region. They usually involve a period of at least two or more days of excessively hot weather.<ref>{{cite web |url=http://www.weather.gov/glossary/index.php?word=heat+wave |title=Glossary |publisher=NOAA's National Weather Service |date=25 June 2009 |access-date=17 July 2013}}</ref> In the [[Northeastern United States|Northeast]], a heat wave is typically when the temperature reaches or exceeds {{convert|90|°F|°C|1}} for three or more consecutive days. This is not always the case. This is because the high temperature ties in with humidity levels to determine a heat index threshold.<ref>{{cite web |last=Singer |first=Stephen |title=Half the country wilts under unrelenting heat |url=http://old.news.yahoo.com/s/ap/us_hot_weather |publisher=Yahoo! News |url-status=dead |archive-url=https://archive.today/20120716024044/http://old.news.yahoo.com/s/ap/us_hot_weather |archive-date=16 July 2012 |df=dmy-all}}</ref> The same does not apply to drier climates. A heat storm is a Californian term for an extended heat wave. Heat storms occur when the temperature reaches {{convert|100|°F|°C|1}} for three or more consecutive days over a wide area (tens of thousands of square miles).<ref>{{cite web|title=Staying Cool and Safe|publisher=[[Pacific Gas and Electric Company]]|location=Oakland, California|date=24 March 2017|accessdate=26 June 2023|url=https://www.pge.com/includes/docs/pdfs/myhome/edusafety/seasonal/coolingcenters/staying_cooling_and_safe_english.pdf|archive-date=27 June 2023|archive-url=https://web.archive.org/web/20230627064913/https://www.pge.com/includes/docs/pdfs/myhome/edusafety/seasonal/coolingcenters/staying_cooling_and_safe_english.pdf|url-status=dead}}</ref> The [[National Weather Service]] issues [[heat advisory|heat advisories]] and [[excessive heat warning]]s when it expects unusual periods of hot weather.

In Canada, heat waves are defined using the daily maximum and minimum temperatures, and in most of the country, the [[humidex]] as well, exceeding a regional threshold for two or more days. The threshold in which daily maximum temperatures must exceed ranges between {{convert|28|°C|°F}} in Newfoundland and {{convert|35|°C|°F}} in interior British Columbia, though this threshold is much lower in Nunavut, ranging between {{convert|22|°C|°F}} and {{convert|26|°C|°F}}.<ref>{{cite web |date=31 Jul 2024|title=Criteria for public weather alerts|url=https://www.canada.ca/en/environment-climate-change/services/types-weather-forecasts-use/public/criteria-alerts.html#heat|access-date=1 Feb 2025 |publisher=Environment and Climate Change Canada}}</ref>

====Oceania====
In Adelaide, South Australia, a heat wave is five consecutive days at or above {{convert|35|°C|°F}}, or three consecutive days at or over {{convert|40|°C|°F}}.<ref>{{cite web |url=http://www.bom.gov.au/announcements/media_releases/sa/20100115_First_Heatwave_SA_Jan.shtml |title=Extreme Heat Services for South Australia |publisher=Bureau of Meteorology |date=15 January 2010 |access-date=17 July 2013}}</ref> The [[Bureau of Meteorology|Australian Bureau of Meteorology]] defines a heat wave as three or more days of unusual maximum and minimum temperatures.<ref name=":0">{{Cite web|title = Australia Weather and Warnings|url = http://www.bom.gov.au/weather-services/about/heatwave-forecast.shtml|publisher = Bureau of Meteorology|access-date = 2016-01-17|language = en|archive-date = 16 October 2015|archive-url = https://web.archive.org/web/20151016140923/http://www.bom.gov.au/weather-services/about/heatwave-forecast.shtml|url-status = dead}}</ref> Before this new Pilot Heatwave Forecast there was no national definition for heat waves or measures of heat wave severity.<ref name=":0" />

In [[New Zealand]], heat waves thresholds depend on local climatology, with the temperature threshold ranging between {{convert|27|°C|°F}} in Greymouth and {{convert|32|°C|°F}} in Gisborne.<ref>{{cite web |date=2024|title=Heat|url=https://getready.govt.nz/emergency/heat|access-date=1 Feb 2025 |publisher=Get Ready - National Emergency Management Agency}}</ref>