Based on the average temperatures over
the past 30 years, much of the United States, and indeed the Northern
Hemisphere, has now entered, or is close to entering, the hottest
time of the year. This was especially the case 107 years ago on July
10, 1913 when the temperature in the shade reached an astounding
134°F in Death Valley, CA. Until just a few years ago, the old world
record for the hottest shade temperature ever recorded was 136.4°F
measured at El Azizia, Libya on September 13, 1922. However, a
special panel of experts from the World Meteorological Organization
(WMO) Commission of Climatology have more recently deemed the Libya record invalid, recognizing the Death Valley all-time high as the
true world record.
The panel of experts from the WMO examined the daily temperature records from El Azizia from 1922 and determined that factors including an inexperienced weather observer, combined with a replacement thermometer, called a Bellani-Six-style thermometer, which is both hard to read and prone to introducing errors, led to the previous world record of 58°C (136.4°F), and because of that, the Libya world record should be deemed invalid.
Death Valley owes much of its record-hot temperatures to the surrounding topography. As described in a previous article, the mountains to the west of the valley squeeze out almost all of the Pacific moisture such that Death Valley is also the driest place in the United States. The long, narrow, below-sea-level valley, surrounded by relatively steep mountains on either side, also serves to reinforce the desert heat. The dry sand and salt flats on the valley floor can heat up to 200°F on the hottest summer days. As this heat rises and cools slightly, it gets trapped from rising completely out of the valley by the surrounding mountains and sinks again, warming even further due to compressional warming. Thus, Death Valley's topography creates a local effect similar to a convection oven.