Millions under heat alert in the U.S.

It is so hot in the United States that corn is sweating. Derek Van Dam reports from Atlanta where a PGA golf tournament is using new technology to beat the extreme heat.

Breaking Heat Records: Phoenix Registers Hottest Month in U.S. History. Hottest Month in U.S. History: The summer of 2023 witnessed a historically intense and prolonged heatwave that swept through the South and Southwest regions of the United States, bringing dangerous triple-digit temperatures to over 70 million Americans.

At the epicenter of this blistering heat was Phoenix, Arizona, which just logged its hottest month on record, setting a new milestone in U.S. weather history. In July, Phoenix experienced an average temperature of a scorching 102.7 degrees Fahrenheit, marking the hottest month ever observed in any U.S. city.

A Record-Shattering Month in Phoenix

Phoenix’s July 2023 will be etched in the history books for the extreme heat it endured. The city’s average temperature of 102.7 degrees Fahrenheit for the entire month was a staggering 3.6 degrees higher than the previous record of 99.1 degrees set in August 2020.

This marked a significant margin for an already lofty record. The relentless heatwave resulted in 31 consecutive days of temperatures at or above 110 degrees, making it the longest streak of 110-plus-degree highs in Phoenix’s recorded history. The previous longest streak was 18 days, set in June 1974.

Notable Temperature Milestones: Hottest Month in U.S. History

The intense heatwave brought several other remarkable temperature milestones during Phoenix’s record-breaking July:

  • Daily Record Highs: Twelve days saw daily record high temperatures, including July 19, 20, and 25, when the mercury soared to a staggering 119 degrees Fahrenheit.
  • Most 115-Degree Days: July experienced a record 17 days with temperatures reaching 115 degrees or greater. The previous record was seven such days in August 2020.
  • Warmest Overnight Lows: The morning low on July 19 was 97 degrees at Sky Harbor International Airport, setting a new record for the warmest overnight low ever recorded in the city. On five nights in July, temperatures failed to fall below 95 degrees, surpassing the previous record of two such nights in any given year.
  • Longest Streak of High Overnight Lows: Phoenix did not experience a temperature drop below 90 degrees from July 10 to July 26, setting a new record for the longest streak of overnight lows at or above 90 degrees. The previous record was seven days in 2020.

Understanding the Factors Behind Extreme Heat

The extreme heat experienced in Phoenix during July can be attributed to a combination of natural and human-caused factors:

  • Natural Variability: Weather patterns play a significant role in temperature fluctuations, and some months are naturally hotter than others due to the inherent randomness of weather. In this case, a stagnant ridge of high pressure, known as a “heat dome,” dominated the weather pattern, bringing in hot, dry, sinking air that suppressed cloud cover and prevented the Southwest monsoon from providing relief.
  • Human-Caused Climate Change: Rising concentrations of heat-trapping greenhouse gases in the atmosphere, primarily from human activities, have intensified the frequency, intensity, and duration of heat events. Since the mid-1890s, Phoenix has warmed by approximately 7.9 degrees during July, reflecting the impacts of climate change.
  • Urban Heat Island Effect: The expanding urban area of Phoenix, characterized by concrete, pavement, and infrastructure, creates an urban heat island effect, wherein cities are notably hotter than surrounding rural areas. This effect contributes to higher temperatures, especially during nighttime.


Phoenix’s record-breaking July of 2023 serves as a poignant reminder of the escalating challenges posed by extreme heat events, and the pressing need for collective action to mitigate the impacts of climate change. As we continue to experience hotter and longer heatwaves, understanding the interplay of natural variability, human-caused climate change, and the urban heat island effect is crucial for developing effective strategies to combat rising temperatures and protect the well-being of communities. As we move forward, concerted efforts to reduce greenhouse gas emissions, promote sustainable urban planning, and prioritize climate resilience will be essential in confronting the impacts of the hottest month ever recorded in U.S. history.

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