2011-06-27 - Driest day in recorded U.S. history

The National Weather Service in Las Vegas, Nevada issued a statement yesterday saying they had reached a record "dew point depression" of 129 degrees (or: low humidity of below 1%) when the local temperature was 107 with a dew point of -22 F.

They explain on their webpage:

"Las Vegas' largest dew point depression ever recorded was set on June 27, 2011 at 129 degrees. The dew point depression is the difference between the air temperature and dew point temperature. At this time the relative humidity was 1%. The previous record dew point depression was 120 degrees set on July 2, 2007. This makes June 27, 2011 the driest day ever recorded based on the dew point depression"

You can't see the maximum depression on the official data graph above, where data only updates once an hour, but they posted a picture of the 1-minute data on their Facebook Page:

Relative humidity readings below 10% were widespread over the Southwest on June 27th 2011, though the KLAS airport was the driest on the Mesonet map.