Map of land surface temperature anomalies for June 17–24, 2012. The map depicts temperatures compared to the 2000–2011 average for the same eight-day period in June. (Land surface temperatures (LST) are distinct from the hot air temperatures that meteorological stations typically measure.)
The Summer 2012 North American heat wave was one of the most severe heat waves in modern North American history. It resulted in more than 82 heat-related deaths across the United States and Canada,[2][3] and an additional twenty-two people died in the resultant June 2012 North American derecho. This long-lived, straight-line wind and its thunderstorms cut electrical power to 3.7 million customers.[4] Over 500,000 were still without power on July 6, as the heat wave continued.[5] Temperatures generally decreased somewhat the week of July 9 in the east,[6] but the high pressure shifted to the west, causing the core of the hot weather to build in the Mountain States and the Southwestern United States shifting eastwards again by mid-July. By early August, the core of the heat remained over the Southern Plains.[7][8]
The heat wave formed when high pressure aloft over the Baja California, Mexico, strengthened and moved over the southern plains around June 20–23 and then spread east and northward, remaining fixed over the center of North America through July 2012.[9][10]
The direct cause of the heat is that, under high pressure, the air subsides (sinks) toward the surface. This sinking air acts as a dome capping the atmosphere. This cap helps to trap heat instead of allowing it to lift. Without the lift there is little or no convection and therefore little or no convective clouds (cumulus clouds) with minimal chances for rain. The result is a continual build-up of heat at the surface resulting in drought conditions over wide areas.[11]
This heat wave, like all extreme weather events, has its direct cause in a complex set of atmospheric conditions that produce short-term weather. However, weather occurs within the broader context of the climate, and many scientists agree that global warming has made it more likely that heat waves of this magnitude will occur.[12][13] A NASA-sponsored study[14] indicates an increase in the drying tendency from spring to summer over the U.S. Central Plains, especially during the transition from June to July. The intensified deficit in precipitation is accompanied by increased downward shortwave radiation flux, tropospheric subsidence, enhanced evaporative fraction, and elevated planetary boundary layer height, all of which can lead to surface drying. These conditions are similar to those accompanying the 2012 drought[15] and intense heat that occurred in mid-summer.
Timeline of impacts
Beginning of heat wave
The intense heat wave in the West was initiated around June 20–23 when the high pressure system centered over the Baja of California shifted upward into the plains[16] and caused temperatures to approach or even surpass 110 °F (43 °C) for the next several days, breaking many records for the area.[citation needed]
The heat spread east from the Rocky Mountains and a massive high-pressure system over the Midwest caused extreme temperatures not seen on such a scale since the 1930s.[17] On June 25, 2012, Denver, Colorado, tied its all-time high with a temperature of 105 °F (40.6 °C). On the same day a couple of 113°F (45°C) readings were recorded in Kansas. The heat was so strong that Alamosa, Colorado, broke its daily record for six consecutive days. In Galveston, Texas, the earliest 100°F (38°C) day ever was recorded.[18]Hill City, Kansas, was the warmest point in the United States on June 26, with the thermometer climbing to 115°F (46.1°C).[19]
In the Mid-South, from June 28 through June 30, many notable temperature extremes occurred. In Paducah, Kentucky, June 29 witnessed an all time official record of 108°F (42.2°C).[citation needed] In Bowling Green, Kentucky, the same day witnessed 109°F (42.8°C), one degree Fahrenheit (0.6 °C) short of the state's all-time record for June. Perhaps more remarkable, Tennessee observed a handful of all-time record highs. Nashville reached 109°F (42.8 °C) on June 30, 11 °F (6.1 °C) higher than the previous record. Knoxville reached a high of 105°F (40.6°C), while Chattanooga reached 107°F (41.7°C), an all-time high, on both June 30 and July 1. And, although not officially verified by the National Weather Service at this time, Smyrna, Tennessee, recorded a reading of 113°F (45.0°C) on the 29th, which would in fact be the highest recorded temperature in the state.[22]
In Fort Good Hope, Northwest Territories, there was a streak of five consecutive days above 30°C (86°F) from June 21 to June 25 peaking at 35°C (95°F), quite possibly the longest heat wave in Canada at that time.[23] Further south, on June 19, 20 and 21, Toronto experienced its first official early season heat wave (In Canada, a heat wave is defined as three or more consecutive days with temperatures at or above 32 °C (89.6 °F)), with temperatures ranging between 33.4 °C (92.1 °F) and 34.5 °C (94.1 °F) and the minimum temperature on June 20 not dropping below 24.4 °C (75.9 °F).[23] On both July 4 and July 6, Toronto reached 36.3°C (97.3°F)[23] and on July 17, the city hit 36.8°C (98.3°F),[23] making this the hottest day of the year in the city and the 5th record daily high of the summer.
The Mid-Atlantic States did not escape the heat. On June 29, Salisbury, Maryland, recorded a monthly record high of 101 °F (38.3 °C),[26] while Baltimore (DMH) reached 106 °F (41.1 °C) on June 29,[27] setting a similar month of June record.
Northeast and Midwest
Chicago's O'Hare International Airport tied its all-time 4th of July record of 102°F (38.9°C) which was set back in 1912. Not far from O'Hare, the official measuring station for the city of Chicago, the villages of Park Ridge, Niles, Norridge as well as much of the Chicago metropolitan area recorded a temperature of 104°F (40°C). Some places north of Chicago got even hotter. Caledonia, Wisconsin, just south of Milwaukee reached 107°F (41.7 °C). Actual air temperatures were close to 110°F (43.3 °C) in and around the city of Allegan, Michigan. St. Louis endured a string of ten straight days with temperatures above 100°F (38 °C), ending on July 7.[28] As of July 7, three deaths in St. Louis were attributed to the heat.[29]
As of July 6, Chicago has had four official 100°F (38°C) or higher temperature readings, one on June 28, along with three in July, culminating with an official near-record shattering high of 103°F (39°C) at O'Hare on both July 5 and 6, reaching 106°F (41.1°C) near Chicago, the following day reaching 98°F shortly before 11am at O'Hare International Airport, but much of the Chicago metro area west and south of the airport reached or exceeded 100 degrees, marking the fourth consecutive day of 100-degree heat across the Chicago area. The city proper tied the old record of three consecutive 100-degree days which was set back in August 1947. Normally, the highest temperature recorded in a typical Chicago summer is around 95°F (35°C), a streak of 3 days above 90°F (32°C) constitutes a "heat wave", and the thermometer reaches or surpasses 100°F (38°C) only once every five to ten years. The Chicago temperatures exceeded the 1995 Chicago heat wave, which claimed over 750 lives, although humidity and registered dew points were higher during that heat wave.[30] Through the first five days of July, the mean temperature in Chicago averaged 86.4°F (30.2°C), 13.2°F (7°C) above normal, the hottest since 1911.[31] Two deaths were confirmed from the heat in Cook County, and two other people died in a train derailment blamed on the heat.[32] An additional death in Rock County, Wisconsin, has been noted.[33]
After a brief respite from the extreme heat, the Mid-Atlantic States resumed observation of record highs by the end of the first week of July. Maryland has been particularly hard-hit, with eight deaths, including four on July 5.[36]Cumberland, Maryland, recorded a monthly record of 104°F (40.0°C) on July 8. Bremo Bluff, Virginia, recorded an astounding 109°F (43°C), which is an all-time-record high on July 8.[37]
The Northeastern United States suffered the worst of the heat wave on July 7–8. Even normally cool plateau regions experienced highs over 90°F. Laurel Mountain, Pennsylvania, near Johnstown, reached 95°F (35.0°C) on July 8, beating the previous all-time-record high by 2°F (1.1 °C). Similarly, on July 7, daily record highs were broken in several cities in eastern Pennsylvania, including Harrisburg, Lancaster, and Chambersburg, which each reached 101°F (38.3°C).[38]Pittsburgh reached 98° on July 7, which, while not a daily record (101° in 1988), was the hottest temperature recorded there since it reached 100° on July 15, 1995. Cleveland, Ohio reached 101°F on July 21. Akron-Canton airport said that it was its warmest year on record with an all time July record of 101°F on July 7.[39] On July 8, the heat eased across the east as the high pressure center shifted west, causing hot weather once again build in the mountain states and the southwest U. S.[7][8][40]
Heat continues in Great Plains, spreads into New England
After some modification in the heat during the past week over the Midwest and Northeast, the jet once again moved further north into Canada allowing intense heat to build across eastern North America. On July 15, Temperatures reached 109°F (42.8°C) in Pierre, South Dakota.
On July 17, the temperature at Detroit, Michigan Metro Airport climbed to 102°F (38.9°C), the third plus 100 degree day thus far in July. The average July maximum temperature is 83°F (28.3°C). On the same date Toronto, Ontario, Canada reached 36.8°C (98.2°F), by July 23 it recorded its fourth daily record high temperature for the month.
The Northeastern states also experienced a second round of heat, with temps again returning to the 90's. Atlantic City, New Jersey, reached 101°F (38.3°C) on July 18, a daily record high. The same day, Newark, New Jersey, reached 104°F (40.0°C), a daily record.[37]Teterboro Airport, NJ recorded a monthly record high of 103°F (39.4°C). Philadelphia, PA hit a temperature of 108°F (42.2°C). Triple-digit temperatures even reached Hartford, Connecticut, where, on July 18, the city reached 100°F (37.8°C), which was a monthly record high.[37]
As of July 25, St. Louis, Missouri endured its 16th straight day of plus 100°F (37.8°C) heat with 27 of the past 28 days exceeding this temperature, with high 90s forecast over the next few days. 24 deaths have been attributed to the heat in St. Louis metro area.[41]
Heat wave continues in the Southwest
As of August 13, 90 to 100-degree plus heat was still occurring in the desert Southwest and in many western states, associated with the same upper-level ridge of high pressure. The heat wave continued at one location or another within the Contiguous US for over two months' worth of consecutive days. A major jet stream dip and associated upper-level trough of low pressure brought rain, storms, and cooler weather to parts of the eastern and central US, slightly lessening drought impacts in some areas.[42]
Other impacts
Wildfires raged across the western United States during the time of the heat wave,[43] in part attributable to the dry conditions caused by the heat. The Waldo Canyon fire in Colorado attracted the most attention after spreading into Colorado Springs and charring hundreds of homes (investigators determined it to be human caused, rather than from "the heat"), but large wildfires also burned throughout Utah, Wyoming, Montana, New Mexico, Arizona and Idaho.[12]
The heat wave also contributed to the record-shattering 2012 North American drought, which caused massive crop failures throughout the Midwest. The drought affected 80% of the contiguous US as of July 24, and was considered the worst drought since the 1950s but not yet on the scale of devastation endured during the Dust Bowl of the 1930s.[44]
On June 29–30, 2012, the heat and humidity from the heat wave caused a small thunderstorm in Iowa to develop into a violent and unprecedented derecho, which tracked across the Midwest and Mid-Atlantic regions of the United States while causing 80 miles per hour (130km/h) or higher winds, doing hundreds of millions of dollars in damage, and downing trees and power lines, leaving four million people in the eastern U. S. without power.[45]
A heat wave or heatwave, sometimes described as extreme heat, is a period of abnormally hot weather. Definitions vary but are similar. A heat wave is usually measured relative to the usual climate in the area and to normal temperatures for the season. Temperatures that humans from a hotter climate consider normal, can be regarded as a heat wave in a cooler area. This would be the case if the warm temperatures are outside the normal climate pattern for that area. High humidity often occurs during heat waves as well. This is especially the case in oceanic climate countries. Heat waves have become more frequent, and more intense over land, across almost every area on Earth since the 1950s, the increase in frequency and duration being caused by climate change.
The July 1995 Chicago heat wave led to 739 heat-related deaths in Chicago over a period of five days. Most of the victims of the heat wave were elderly poor residents of the city, who did not have air conditioning, or had air conditioning but could not afford to turn it on, and did not open windows or sleep outside for fear of crime. The heat wave also heavily impacted the wider Midwestern region, with additional deaths in both St. Louis, Missouri and Milwaukee, Wisconsin.
The 1980 United States heat wave was a period of intense heat and drought that wreaked havoc on much of the Midwestern United States and Southern Plains throughout the summer of 1980. It was among the most destructive and deadliest natural disasters in U.S. history, claiming at least 1,700 lives. Because of the massive drought, agricultural damage reached US$20 billion. It is among the billion-dollar weather disasters listed by the National Oceanic and Atmospheric Administration.
The climate of Chicago is classified as hot-summer humid continental with hot humid summers and cold, occasionally snowy winters. All four seasons are distinctly represented: Winters are cold and often see snow with below 0 Celsius temperatures and windchills, while summers are warm and humid with temperatures being hotter inland, spring and fall bring bouts of both cool and warm weather and fairly sunny skies. Annual precipitation in Chicago is moderate and relatively evenly distributed, the driest months being January and February and the wettest July and August. Chicago's weather is influenced during all four seasons by the nearby presence of Lake Michigan.
The Summer 2006 North American heat wave was a severe heat wave that affected most of the United States and Canada, killing at least 225 people and bringing extreme heat to many locations. At least three died in Philadelphia, Arkansas, and Indiana. In Maryland, the state health officials reported that three people died of heat-related causes. Another heat related death was suspected in Chicago.
The 2006 European heat wave was a period of exceptionally hot weather that arrived at the end of June 2006 in certain European countries. The United Kingdom, France, Belgium, the Netherlands, Luxembourg, Italy, Poland, the Czech Republic, Hungary, Germany and western parts of Russia were most affected.
A cold wave is a weather phenomenon that is distinguished by a cooling of the air. Specifically, as used by the U.S. National Weather Service, a cold wave is a rapid fall in temperature within a 24-hour period requiring substantially increased protection to agriculture, industry, commerce, and social activities. The precise criteria for a cold wave are the rate at which the temperature falls, and the minimum to which it falls. This minimum temperature is dependent on the geographical region and time of year.
The 1936 North American heat wave was one of the most severe heat waves in the modern history of North America. It took place in the middle of the Great Depression and Dust Bowl of the 1930s and caused more than 5,000 deaths. Many state and city record high temperatures set during the 1936 heat wave stood until the 2012 North American heat wave. Many more endure to this day; as of 2022, 13 state record high temperatures were set in 1936. The 1936 heat wave followed one of the coldest winters on record.
Minnesota has a humid continental climate, with hot summers and cold winters. Minnesota's location in the Upper Midwest allows it to experience some of the widest variety of weather in the United States, with each of the four seasons having its own distinct characteristics. The area near Lake Superior in the Minnesota Arrowhead region experiences weather unique from the rest of the state. The moderating effect of Lake Superior keeps the surrounding area relatively cooler in the summer and warmer in the winter, giving that region a smaller yearly temperature variation. On the Köppen climate classification, much of the southern third of Minnesota—roughly from the Twin Cities region southward—falls in the hot summer zone (Dfa), and the northern two-thirds of Minnesota falls in the warm summer zone (Dfb).
The 2007 North American heat wave started at the end of July and lasted into the first weeks of August. It was associated with severe drought over regions of the southeastern United States and parts of the Great Lakes region.
North Dakota's climate is typical of a continental climate with cold winters and warm-hot summers. The state's location in the Upper Midwest allows it to experience some of the widest variety of weather in the United States, and each of the four seasons has its own distinct characteristics. The eastern half of the state has a humid continental climate with warm to hot, somewhat humid summers and cold, windy winters, while the western half has a semi-arid climate with less precipitation and less humidity but similar temperature profiles. The areas east of the Missouri River get slightly colder winters, while those west of the stream get higher summer daytime temperatures. In general, the diurnal temperature difference is prone to be more significant in the west due to higher elevation and less humidity.
The 2010 Northern Hemisphere summer heat waves included severe heat waves that impacted most of the United States, Kazakhstan, Mongolia, China, Hong Kong, North Africa and the European continent as a whole, along with parts of Canada, Russia, Indochina, South Korea and Japan during July 29, 2010. The first phase of the global heatwaves was caused by a moderate El Niño event, which lasted from June 2009 to May 2010. This lasted only from April 2010 to June 2010 and caused only moderate above-average temperatures in the affected regions, but it also set new record high temperatures for most of the area affected in the Northern Hemisphere.
The 2011 North American heat wave was a deadly summer 2011 heat wave that affected the Southern Plains, the Midwestern United States, Eastern Canada, the Northeastern United States, and much of the Eastern Seaboard, and had Heat index/Humidex readings reaching upwards of 131 °F (55 °C). On a national basis, the heat wave was the hottest in 75 years.
In March 2012, one of the greatest heat waves was observed in many regions of North America. Very warm air pushed northward west of the Great Lakes region, and subsequently spread eastward. The intense poleward air mass movement was propelled by an unusually intense low level southerly jet that stretched from Louisiana to western Wisconsin. Once this warm surge inundated the area, a remarkably prolonged period of record setting temperatures ensued.
The 2013 extreme weather events included several all-time temperature records in Northern and Southern Hemisphere. The February extent of snow cover in Eurasia and North America was above average, while the extent of Arctic ice in the same month was 4.5% below the 1981–2010 average. The Northern Hemisphere weather extremes have been linked to the melting of Arctic sea ice, which alters atmospheric circulation in a way that leads to more snow and ice.
The 2018 Britain and Ireland heatwave was a period of unusually hot weather that took place in June, July and August. It caused widespread drought, hosepipe bans, crop failures, and a number of wildfires. These wildfires worst affected northern moorland areas around the Greater Manchester region, the largest was at Saddleworth Moor and another was at Winter Hill, together these burned over 14 square miles (36 km2) of land over a period of nearly a month.
The 2021 Western North America heat wave was an extreme heat wave that affected much of Western North America from late June through mid-July 2021. The heat wave affected Northern California, Idaho, Western Nevada, Oregon, and Washington in the United States, as well as British Columbia, and in its latter phase, Alberta, Manitoba, the Northwest Territories, Saskatchewan, and Yukon, all in Canada. It also affected inland regions of Central and Southern California, Nevada, and Montana, though the temperature anomalies were not as extreme as in the regions farther north.
In 2022, several areas of the world experienced heat waves. Heat waves were especially notable in East Asia, the Indian subcontinent, Australia, western Europe, the United States, and southern South America. 2022 heat waves accounted for record-breaking temperatures and, in some regions, heat-related deaths. Heat waves were worsened by the effects of climate change, and they exacerbated droughts and wildfires.
From late spring to late summer heat waves in 2022 smashed many records in North America between May and September of that year. Dozens of temperature records were surpassed in the United States.
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