Weatherdem's Weblog

Bridging climate science, citizens, and policy

Hottest July on Record for Denver, CO


As expected, July 2012 went down in the history books as the hottest July in recorded history (140+ years) for Denver, CO.  A large number of cities echoed this theme throughout the High Plains and Midwest.  I will cover some of those places in future posts.  This post is all about the capital city of Colorado.

The average temperature in Denver during July, 2012 was 78.9°F.  That value is 4.7°F above normal – so Denver regularly experiences rather warm Julys: 74.2°F.

July 2012 is also very likely to go down in the books as the hottest month ever in Denver’s history.  I posted this information recently and here it is again: the confirmed hottest month in Denver history prior to July 2012 was July 1934 – during the middle of the Dust Bowl years – with an average temperature of 77.8°F:


77.8 1934 #
77.7 2005
77.6 2008
77.3 1936
77.1 1939
76.9 1966, 2003
76.8 1954
76.7 2000, 2001
76.6 1901
76.4 1980

Beating a monthly average temperature record by 1.1°F is significant.  It is even more significant when you consider June 2012 was also the warmest June on record at 75.0°F, which was an astounding 7.6°F warmer than normal!  June 2012 beat June 2004 for the warmest June on record by an also significant 1.5°F.  To put it in a nutshell: 2012 has been extremely warm.

July 2012 missed another top-10 listing – this one for precipitation.  With the weak return of monsoon flow near the end of the month, 0.06″ of rain fell, which pushed July 2012’s precipitation total all the way up to … 0.48″.  That is 1.68″ below average.  But it was enough to rank July 2012 as the 11st driest July on record, missing the top-10 by 0.03″ (1920).

Consecutive 90°F-day streak

I have also recently written about the long strings of 90°F+ days Denver has experienced (suffered?).  Through the end of July, Denver has recorded 21 straight days of 90°F+ maximum temperatures.  That is the 2nd longest such streak in Denver’s recorded history (the longest so far is 24).  There was another long streak from late June through early July: 15 consecutive days.  2012 will be only the 4th year that 2 separate 10+ day streaks occurred during the same calendar year.  The longest streak could be seriously challenged this year: today and the next two days’ high temperatures are predicted to be 90°F+.  Saturday could end the streak as the upper-level ridge of high pressure shifts to the east slightly and a weak cool front moves over Denver from the north: Saturday’s high is expected to be 85°F, then return to 90°F+ Sunday.

The total number of 90°F+ days so far in 2012 is now 46: 2 in May, 17 in June, and 27 in July.  Those 27 90°F+ days in July also set another record.  The previous record was 26, set in 2000 and 2008.  In Denver’s recent climatological period, an average of 32 90°F+ days occur.  8 more days of 90°F+ temperature need to occur in 2012 to get into the top-9 list with 50 days.  The year with the most 90°F degree days was 2000 with 61.  Given the extensive heat that has occurred so far in 2012, I would not be surprised to see that record challenged.  Of course, it will take at least 2 more weeks to see how realistic such an event might be.

The seven days of 100°F+ in July 2012 ties the record set in 2005.  Of course, the six 100°F+ days in June 2012 set its own record.  The combination of 100°F+ days in June and July (13 days) also set a significant record by almost doubling the record set in 2005.

Lastly, this summer could be a really bad anomaly that is mostly natural or it could be caused in part by our changing climate.  Tying specific events such as the 2012 heat wave and drought to climate change is an extremely difficult proposition given the relative lack of robust observational data.  It is further challenged by the occurrence of multi-decadal droughts and heat waves that occurred in the geologically recent past (i.e., within the past 2000 years).  Clearly, those events were not anthropogenic in nature.  Discerning the influence of anthropogenic forcing on current and recent droughts is not straightforward.  As with many other phenomena, we might have to wait decades still before such signals are identified in the observational record.  Suffice to say, this year’s North American heat wave and drought are severe and anomalous.  It remains to be seen how much resilience and capacity is possessed by affected societies.  One bad year is easily survived given the state of technology we possess.  How many bad years might be necessary to challenge that technological state?  How robust are our agricultural and water resource policies, to name just a couple?  How much of a shock can our economic system handle given current weaknesses that remain unaddressed?


3 thoughts on “Hottest July on Record for Denver, CO

  1. Pingback: Denver’s Temperatures Continue March To Records « Weatherdem’s Weblog

  2. Pingback: Denver Ties Record For Most 90°F+ Days « Weatherdem’s Weblog

  3. By Any Chance, do you have even more posts like the following 1 titled, Hottest July on Record
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