The Las Vegas National Weather Service office posted this today (this is a weather record that I don’t think I have ever heard of!):

.. All-time record dew point depression set at Las Vegas today…

At 432 PM PDT today the dew point depression at McCarran International Airport in Las Vegas reached 129 degrees. The dew point depression is defined as the difference between the air temperature and the dew point temperature. In the case of today the air temperature was 107 degrees at 432 PM and the dew point temperature was -22 degrees. This made for a relative humidity of 1 percent at the time. The previous all-time record dew point depression for Las Vegas was 120 degrees set on July 2nd 2007.

The above information is preliminary and is subject to a final review before being certified by the National climatic data center.

I couldn’t find how this compares with other dry spots or what the world record is for dew point depression. However, a very good explanation on dew points and relative humidity (and why anyone saying it it was 90° with 90% humidity is most likely lying unless they just came back from Eritrea or the Middle East) can be found here.

Interestingly, the most humid it ever was in Las Vegas was a dew point of 73° set on 7/2/2007 and 7/8/1999. Link.

Wait a second. Hmm. The most humid and driest day. On the same day. That must be an error as it is unlikely the driest and wettest days in Las Vegas history were the same day. Let’s look at Weatherspark’s history for Las Vegas (a very cool weather visualization site where you can compare history, currently conditions, forecasts, and averages graphically).

Yep, looks like that was a very dry day. It didn’t have a dew point of 73°. It was well below zero that day. Here is the graph for the really humid day — 7/8/1999. That’s better. Horribly humid with a thunderstorm and rain. But correct.

I never thought I’d see an error on the Internet. I’ll notify the authorities.