Phoenix heat sets records day and night. Is relief on the way?

Earlier in the morning, the overnight low dropped only as far as 97 degrees in Phoenix, tying the warmest low ever recorded, also set back in 2023, on July 19.

Those are the only two times it's been that warm at night since observations began in 1895.

In fact, temperatures Thursday night were only below 100 for three hours, recorded between 4:25 a.m. and 7:30 a.m. Friday morning. The average nighttime temperature at this time of year is 85 , so that's far above the mark.

With Saturday expected to be the hottest day of this weekend's heat wave, Phoenix faced the risk of nearing the nighttime record again.

Some forecasts for Saturday predicted up to 118 degrees. The record for July 25 is 119. 

Is a 100-degree low that far off? While temperatures are pushing record highs this weekend, it would require a lot of daytime heat to reach that point and not cool off enough overnight — we're not quite there yet.

Extreme heat warnings remain in effect in metro Phoenix and southwestern Arizona through Monday evening for the aggressive temperatures.

The heat itself is due to the proximity of upper-level high pressure to Arizona, which brings subsiding air that suppresses thunderstorm activity by limiting instability, along with some drier air.

Temperatures remain so warm at night because of the urban heat island effect — metals, glass, concrete and other materials hold onto the high heat built up during the day and dominate our landscape at night.

The good news is that this pattern is not long-lasting. That high pressure will slowly lift up toward Colorado, allowing for increasingly better easterly flow that will allow isolated storm activity in southeastern Arizona and other nearby higher elevations.