Unlike most desert locations which have drastic fluctuations between day and nighttime temperatures, the urban heat island effect limits Phoenix's diurnal temperature variation. As the city has expanded, average summer low temperatures have been steadily rising. Pavement, sidewalks, and buildings store the Sun's heat and radiate it at night. The daily normal low remains at or above for an average of 74 days per summer. On July 19, 2023, at the height of an unprecedent heatwave that caused daily highs to top or higher that lasted for 31 days straight, Phoenix set its record for the warmest daily low temperature, at .
unlike most desert locations which have drastic fluctuations between day and nighttime temperatures the urban heat island effect limits phoenix's diurnal temperature variation as the city has expanded average summer low temperatures have been steadily rising pavement sidewalks and buildings store the sun's heat and radiate it at night the daily normal low remains at or above for an average of 74 days per summer on july 19 2023 at the height of an unprecedent heatwave that caused daily highs to top or higher that lasted for 31 days straight phoenix set its record for the warmest daily low temperature at 