World’s Hottest Nights/Highest Minimum Temperatures Yet Measured

Published: 21:31 GMT le 21 novembre 2016

World’s Hottest Nights/Highest Minimum Temperatures Yet Measured

One of the interesting facets of global warming has been how, over the past several decades, nighttime minimum temperatures have become warmer relative to daytime maximum temperatures. There are several scientific explanations for this. A recent study (published in the International Journal of Climatology in February 2016 by Richard Davy et al at the Bjerknes Centre for Climate Research posits that the primary reason is that “night-time temperatures are inherently more sensitive to climate forcing”. See for more about this hypothesis and this for the full article. The focus of this blog, however, is simply an attempt to correlate a list of the extremes for record maximum-minimum temperatures from available data.

The blog consists of the figures of record daily maximum-minimum temperatures observed in the world and particularly the U.S. I should note, of course, that there is a difference between the ‘hottest night’ and ’the ‘warmest daily minimum’ temperatures since the temperature may, during the evening fall lower than the previous morning’s low temperature. It is difficult to determine just what the ‘hottest night’ on record may be for any given location. Temperature data is formatted and published to measure ‘calendar days’ rather than ‘24-hour periods’ since Excel files can’t handle more than one figure per column (at least that is the reason I’m given by those I’ve asked about this). That story is for a future blog. The statistics provided in this blog are for ‘daily record maximum-minimum temperatures’.

World Records for Highest Daily Minimum Temperature

Global average temperature trends over the past 50 years as researched by Richard Davy et al in the recent study (published in the ‘International Journal of Climatology’ in February 2016. For the northern hemisphere the most pronounced effect was during the winter months: +0.18°K whereas the summer months saw about a 0.11°K rise. Graph from ‘International Journal of Climatology’ February 2016.

It would appear that two sites in the world more or less tie for the warmest daily minimum temperature yet measured: Death Valley in the U.S. with 107°F (41.7°C) on July 12, 2012 and 41.7°C (107.1°F) at Khassab Airport, Oman on June 27, 2011. Since the conversions between F° and C° can make a difference of 0.1°F it is a statistical tie between the two sites. It should also be noted that since the NWS in the U.S. rounds down minimum temperatures and up maximum temperatures to the nearest 1°F, the actual temperature measured in Death Valley could have been anywhere from 106.6°F to 107.5°F (41.4°-41.9°C).

Below is table of the highest daily minimum temperatures measured by continent:

Record maximum-minimum temperatures so far observed by continent. This information is courtesy of Maximilliano Herrera.

Aside from the U.S. and Australia, it is difficult to pin down max-min temperature records for other individual nations or cities. Most national weather service web sites do not provide this information. From gleaning information I’ve found on the internet (words of caution there!) here are a few contenders.

United Kingdom: 23.9°C (75.0°F) at Brighton on August 4, 1990.
Netherlands: 24.1°C (75.4°F) at Limburg on July 2, 2015.
Germany: 26.7°C (80.1°F) at Weinbeit bei Neustadt on Aug. 7, 2003
Greece: 35.8°C (96.4°F) at Paleochora on June 27, 2007

It is frustrating that I am unable to find what Canada’s record for this might be. Toronto’s record is 26.6°C (79.9°F) on July 21, 2011, but it is likely other locations (probably many) have seen warmer lows elsewhere in the country, especially in southern Saskatchewan and Manitoba during the intense summer heat waves of the 1930s (Bismarck, North Dakota had a minimum of 83°F/28.3°C in July 1936). Hopefully, one of the readers of this blog knows the answer.

The national weather service for France, Meteo France, maintains an excellent web site full of weather-record information but not so far as record high minimums. These most likely would have occurred during the deadly heat wave of August 2003 (see national record for Germany above). Apparently, Paris endured its hottest night ever on August 12, 2003 when the temperature failed to fall below 25.5°C (77.9°F), but just what the national record for France might be escapes me. Perhaps Jerome or Max can answer this.

U.S.A Records for Highest Daily Minimum Temperature

The trend in the U.S. also reflects (to a smaller degree) the global increase in daily minimum temperatures versus daily maximum temperatures over time, as reported in Davy’s article.

The top graph(s) shows how on an annual basis (in this case the 12-month period from November-October, 2016) the maximum temperatures have been rising by an average of +0.13°F per decade whereas the minimum temperatures by +0.15°F per decade. In the bottom graph(s) we see the temperature changes, since 1901, broken down into winter and summer seasons. In these cases there is a pronounced bias toward warmer summer temperature minimums relative to warmer summer temperature maximums: +.14°F per decade for minimums versus +.07°F for maximums, in other words the summer nights are warming twice as fast as the summer days in the U.S. The winter months show very little difference in this regard. Note that this does not correlate with the Davy report. However, the Davy report was for hemispheric observations and with a 50-year POR baseline. The NOAA report has a 100-year POR baseline. So the two graph’s are not comparable all things being equal. Graphs from NOAA: Climate at a Glance.

Researching this subject for individual sites in the U.S. is relatively easy using the NCDC’s ‘NOW Data’ available for thousands of weather stations (including COOPs) across the country. The biggest problem is that there are some quality control problems with this database; some obvious.

Nowhere in the country (and perhaps the world) has nights as hot as Death Valley where, on a few days some summers, the temperature fails to fall below 100°F. The only other 100°F+ minimum site I can find is Bullhead City, Arizona which claims a low of 102F° on July 26, 2006 (this according to NOW data, WU has the 102° figure occurring on July 22nd). Death Valley’s world-tying low of 107°F on July 12, 2012 does not include a pair of very dubious reports from Greenland Ranch in August 1924 of lows of 110°F (43.3°C) on Aug. 25 and 26 and again on July 5, 1918 (equally dubious). Looking at the COOP form for August 1924 one can see a number of irregularities: extremely small diurnal temperature spreads of only 6° on Aug. 19th, a twelve-day continuous stretch of minimums of 100° (and 110°). In the modern history (since 1934) of Death Valley’s weather record the longest stretch of consecutive days above 100°F has only been three.

The COOP form for Greenland Ranch in Death Valley for August 1924. Two nights reportedly had minimum temperatures of 110°F (43.3°C). However, a close examination of this form shows a number of irregularities. The two 110°-figures cannot be considered genuine. Similar scrutiny of the COOP form for July 1918, when another minimum of 110° was reported, is also suspicious.

Outside of the desert Southwest the highest daily minimum temperatures I’ve found so far were 92°F (33.3°C) at Leavenworth, Kansas on Aug. 10, 1934 and 91°F (32.8°C) at Lincoln, Nebraska on July 25, 1936.

One of the hottest nights ever endured in the U.S. outside of the desert Southwest occurred on the night of July 25, 1936 at the unlikely location of Lincoln, Nebraska, when the temperature fell to only 91°F (32.8°C). The citizens of the city spent the night outdoors trying to sleep on the lawn of the state capitol. Photo from the archives of the Nebraska State Historical Society.

On the other side of the coin, the U.S. site (including Alaska) with the record coolest highest minimum summer temperature on record is 51°F (10.6°C) at Leadville, Colorado on July 20, 2010. Leadville is located at an elevation of 10,152’ (3094 meters) and is the highest incorporated city in the entire country. It should be noted, however, that the POR (period of record) for Leadville only goes back to 1976. Eureka, California has the coolest record daily max-min for any first-order site with a long POR: a 63°F reading last set on January 18, 1981! There were two other occasions with a daily record max-min of 63°: Feb. 26, 1980 and Aug. 27, 1894. In Alaska, Barrow holds this record (for a first order site) with a 53°F record (see table below)

Below is a table of the highest minimum temperatures on record for most major cities in the U.S., arranged by both temperature and date of occurrence. Most of these sites have POR’s dating back to the 19th century. Although one can see a plethora of post-2000 records. However, many of these were tied with earlier dates and, in addition, this is too small a sample of sites to draw any conclusions from, although one could argue there is a trend here. The summer of 2016 was a great example of how record high minima made all the difference so far as the summer’s ranking as the fifth hottest on record (it was the warmest summer on record so far as minimum temperatures were concerned. See this blog posted by Bob Henson on WU in September for more details.

NOTES ABOUT THE TABLE ABOVE: NOW data for Anchorage, Alaska only goes back to 1953, thus I did not include this significant site on the table. Since 1953 the max/min temperature record for Anchorage is 63° on July 10, 2005.

A minimum of 76° on June 26, 1915 reported in NOW data for Fairbanks, Alaska is suspicious.

Denver, Colorado NOW data has two highly suspicious minimums of 77° and 76° both set in the summer of 1881. No other year since then (or before) has seen a daily minimum warmer than the 73° reading in 2003.

Indianapolis has two suspicious minimums of 85° and 84° both reported during the summer of 1874.

Hopefully, some readers of this blog can suggest new data (especially for non-U.S. sites) to build on this initial effort.

KUDOS: Thanks to Mark Stroud of Moon Street Cartography for the table production above, and Maximilliano Herrera for the continental highest minimum temperatures.

Christopher C. Burt

Weather Historian

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Christopher C. Burt is the author of 'Extreme Weather; A Guide and Record Book'. He studied meteorology at the Univ. of Wisconsin-Madison.

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