Rising Overnight Lows and Dangerous Heat Wave Grip Southwest U.S.

Phoenix, Arizona is experiencing an increase in overnight low temperatures, primarily due to the urban heat island effect. The number of consecutive days hitting 110 degrees has also been on the rise, with the ongoing heat wave ranking fourth between 2007 and 2020. Daily lows between June 1 and July 9 have been trending up since temperature recording began in 1896. The increase in lows has had a significant impact on heat waves, with last year's extended wave of over 110 degrees having a daily average of 100.8 degrees.