12:10 PM | *Hottest temperature ever recorded took place on July 10th, 1913 in Death Valley, California – but there is an interesting twist to the record*

Actual observations at Death Valley, CA in the days surrounding the hottest temperature ever recorded; Source: http://docs.lib.noaa.gov/rescue/mwr/050/mwr-050-01-0010.pdf

Overview
The forecast for the high temperature in Death Valley, California for the next couple of days is a rather pedestrian 108 degrees or so. One hundred and three years ago – on July 10th, 1913 - the weather observer at Greenland Ranch in Death Valley recorded a high temperature of 134 degrees. This is the highest air temperature ever reliably recorded on Earth, but it didn’t get that distinction until just recently. The Greenland Ranch weather station was located across the street from what is known today as the Furnace Creek Ranch and it is about 180 feet below sea level.

View of Death Valley National Park, CA from asphalt road

Discussion
Death Valley National Park is the largest national park in the continental US and is located in the Mojave Desert of southeast California. It contains a vast range of elevations and landscapes and is known for being a land of extremes including its climate. In fact, the depth and shape of Death Valley contribute greatly to its extreme heat. Specifically, the extreme heat is due to a combination of several factors including the elevation below sea level, the lack of vegetation especially on the lowest part of the valley floor which allows sunlight to directly heat the desert surface, the narrow width of the valley and its north-south orientation which traps air in the valley allowing it to be recycled back down to the valley floor, radiation of heat from the rocky surfaces of the mountains that surround the valley, and the low humidity as dry air heats at a much quicker rate than moist air. Temperatures in Death Valley normally reach or exceed 100 degrees from Mid-May until early October.

During July of 1913, Death Valley endured an intense stretch of hot weather from the 5th through the 14th when the high temperature reached 125 degrees or higher each and every day. In fact, this 10 day stretch still ranks as the hottest stretch of weather ever recorded in Death Valley. The hottest days in this stretch occurred from the 9th through the 13th when the high temperature reached at least 129 degrees with the hottest being on July 10th when the record-breaking 134 degrees was measured.

Twist to the record
And now for an interesting recent twist to the story. The Death Valley record of 134 degrees was less than a decade old when it fell to a new record. On September 13, 1922, a temperature of 136 degrees was recorded at El Azizia, Libya and this was indeed cited by the World Meteorological Organization (WMO) for nine decades as the world’s highest temperature ever recorded. However, on September 12th, 2012, the WMO officially re-certified the 134 degree reading of July 10th, 1913 at Death Valley as the all-time highest air temperature ever recorded on Earth after evidence surfaced suggesting the Libya record of 136 degrees was based on a reading from a bad thermometer which was placed in the wrong place (near asphalt) and, in addition, read by an untrained observer.

This particular example of the rewriting of weather history actually cites the many difficulties of comparing high temperature records of today to those from decades ago. One important problem has to do with the fact that many official weather stations have had significant growth in development (housing, roads, etc.) in the immediate regions surrounding the stations. Materials such as asphalt and concrete that are generally connected with urban development are known to have an (warming) impact on temperature readings. This “urban heat island” effect has become an increasingly important problem in the analysis of long-term temperature trends. In the Southwest US, for example, where populations have doubled or tripled in the past 50 years near official weather stations (e.g. Las Vegas, Phoenix), the problem has become quite serious making record high temperature records of today somewhat dubious in certain locations. Even the inhospitable region of Death Valley has had some development in the area surrounding the Furnace Creek weather station with asphalt roads now leading to the nearby visitor’s center - all of which makes this long-surviving 103-year old record of 134 degrees very impressive indeed.

Meteorologist Paul Dorian

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