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 and caused temperatures to approach or even surpass 110 °F (43 °C) for the next several days, breaking many records for the area. 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. 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.
Hill City, Kansas, was the warmest point in the
United States on June 26, with the thermometer climbing to 115 °F (46.1 °C). Thousands of records were again broken on June 28.
Fort Wayne, Indiana, tied its all-time record high with 106 °F (41.1 °C) while
Indianapolis broke its monthly record at 104 °F (40 °C). More monthly records that day included
St. Louis, Missouri, at 108 °F (42.2 °C) and
Little Rock, Arkansas, at 107 °F (41.7 °C). The heat resulted in two boys from
Bradley County,
Tennessee, dying of
hyperthermia. 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 . In
Bowling Green, Kentucky, the same day witnessed , 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 , while
Chattanooga reached , 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 on the 29th, which would in fact be the highest recorded temperature in the state. 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. 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). On June 30,
Atlanta, Georgia, set a new all-time record high temperature of 106 °F (41.1 °C). A statewide record high was even set across the entire state of
South Carolina. 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), while
Baltimore (
DMH) reached 106 °F (41.1 °C) on June 29, 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. As of July 7, three deaths in St. Louis were attributed to the heat. As of July 6, Chicago has had four official or higher temperature readings, one on June 28, along with three in July, culminating with an official near-record shattering high of at O'Hare on both July 5 and 6, reaching near
Chicago, the following day reaching 98 °F shortly before 11 am 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 , a streak of 3 days above constitutes a "heat wave", and the thermometer reaches or surpasses 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. Through the first five days of July, the mean temperature in Chicago averaged , above normal, the hottest since 1911. Two deaths were confirmed from the heat in
Cook County, and two other people died in a
train derailment blamed on the heat. An additional death in
Rock County,
Wisconsin, has been noted. The heat caused highways to buckle in
Illinois,
North Carolina, and Wisconsin. 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.
Cumberland, Maryland, recorded a monthly record of on July 8.
Bremo Bluff, Virginia, recorded an astounding , which is an all-time-record high on July 8. 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 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 .
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. 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.
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 in
Pierre, South Dakota. On July 17, the temperature at
Detroit,
Michigan Metro Airport climbed to , the third plus 100 degree day thus far in July. The average July maximum temperature is . On the same date
Toronto, Ontario, Canada reached , 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 on July 18, a daily record high. The same day,
Newark, New Jersey, reached , a daily record.
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.
Other impacts Wildfires raged across the western United States during the time of the heat wave, 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. 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.
Severe storms moved from Indiana to Virginia. 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 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. ==See also==