A friend pointed out to me that some remarkably large dewpoint depressions have been reported McCarran International Airport in Las Vegas (KLAS) the past few days. The dewpoint depression is the difference between the temperature and the dewpoint. Yesterday, the dewpoint depression at KLAS reach 101ºF at 1500 PDT when the temperature was 102ºF and the dewpoint only 1ºF. That's a relative humidity of 2.3%.
Impressive, although if you look at the graph above you can see that on May 29 there was an observation with a dewpoint depression of 104ºF when the temperature was 93ºF and the dew point -11ºF.
Inspection of the minimum dewpoints over the past 24-h shows that KLAS is the big winner for the lowest in the Las Vegas area, although there is a site on the slopes of Mount Charleston that bottomed out at 2ºF.
How trustworthy the dewpoint observations are at these very low relative humidities is unclear, but the saying "but it's a dry heat" applies pretty well this week.