The History of Extreme Heat in Phoenix: Revisiting the Summer of 1990

Phoenix, Arizona, recorded an all-time high temperature of 122 degrees Fahrenheit on June 26, 1990, according to the National Weather Service (NWS). While anecdotal reports often cite higher figures, official meteorological data confirms this 122-degree reading remains the city’s highest temperature since record-keeping began at Sky Harbor International Airport in 1895. This event serves as a historical benchmark for extreme heat in the American Southwest.

How the 1990 Heatwave Compares to Modern Records

The 1990 record stood as the undisputed peak for three decades before being tied during a severe heatwave in 2017. On June 19, 2017, the NWS again confirmed a high of 122 degrees at Sky Harbor. The proximity of these two events highlights the persistence of extreme heat patterns in the Sonoran Desert. Prior to 1990, the previous record was 118 degrees, set in 1905 and tied several times throughout the mid-20th century. The jump to 122 degrees represented a significant shift in the intensity of regional summer weather events.

Why Phoenix Experiences Such Extreme Temperatures

The geography of the Salt River Valley, combined with the urban heat island effect, contributes to the city’s high temperature readings. According to the Environmental Protection Agency (EPA), urban heat islands occur when cities replace natural land cover with dense concentrations of pavement, buildings, and other surfaces that absorb and retain heat. In Phoenix, the reliance on concrete and asphalt prevents the ground from cooling effectively at night. This creates a cumulative effect where daily minimum temperatures remain high, preventing the body from recovering from daytime heat exposure.

The Impact of Historical Heat on Public Policy

The 1990 heat event prompted changes in how municipal authorities manage extreme weather. The Maricopa County Department of Public Health now tracks heat-associated deaths with increased granularity, noting that the combination of high humidity and high overnight lows poses the greatest risk to public health. Unlike the 1990s, when heat alerts were less frequent, the city now utilizes a sophisticated heat-monitoring network to trigger cooling centers and public health warnings when forecasts predict temperatures exceeding 110 degrees for multiple consecutive days.

Key Data Points on Phoenix Heat

• All-time record high: 122°F (June 26, 1990; June 19, 2017)
• Primary driver: High-pressure “heat domes” that trap air over the Southwest
• Risk factor: Urban heat island effect increasing nighttime baseline temperatures
• Monitoring agency: National Weather Service, Phoenix Office

What Happens During Prolonged Heat Events?

When temperatures reach 120 degrees or higher, infrastructure and human physiology face significant stress. The Centers for Disease Control and Prevention (CDC) notes that at these levels, the body’s ability to cool itself through sweat is severely compromised. Beyond the human impact, regional power grids experience increased demand for air conditioning, and aviation operations may be restricted. In 1990, extreme heat led to the cancellation of flights at Sky Harbor, as the air density at high temperatures reduced the lift required for aircraft to take off safely—a protocol that remains standard practice for major airlines operating in the region today.