Weatherdem's Weblog

Bridging climate science, citizens, and policy

Graphical History of 100 Degree Days in Denver & Possible Warmest July/Month


After a little bit of digging, I found the local NWS Office’s list of 100 degree days in Denver since 1872 – a 140 year history.  I’ve graphed number of occurrences by year:


The data is valid through the 28th of July, 2012.  As I’ve stated in previous posts, the previous yearly maximum number of occurrences took place in 2005 with 7.  So far this year, the temperature has exceeded 100°F 13 times.  At this point, I do not expect the NWS to record another 100°F day during the rest of this year.  While it has been warmer than normal in Denver, the North American monsoon season has kicked into gear, which suppresses daily maximum temperatures due to cloud formation.  The afternoons cannot get as warm with widespread, thick clouds as they could prior to the monsoon when the sun warmed the ground throughout the day.

Note that while 100°F day incidence appears to be increasing, I am not making any claim as to the statistical significance of such a development.  The linear trend (not shown) over the entire dataset is slightly positive, but these events are too rare from which to draw robust conclusions.

That said, the average temperature through the 28th of July in Denver is 78.9°F.  The Denver/Boulder NWS Office has the top-10 warmest Julys list:


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

With only three days remaining, July 2012 has a very legitimate shot at the hottest July in 140 years’ of record-keeping.  If the average temperature remains near 78.9°F, 2012 will also beat out 1934’s 77.8°F by over 1°F!!  And while the 1930s were a very warm decade, note further that 5 of the warmest Julys on record occurred during the 2000s.

What is the `#` symbol in the table?  The NWS notes this:

# Warmest Month in Denver History.

If July remains anomalously warm from today through Tuesday, July 2012 will be the warmest month in Denver history.  This follows on the heels of the hottest June on record: 75°F, which beat the old record of 73.5°F (June 1994).


6 thoughts on “Graphical History of 100 Degree Days in Denver & Possible Warmest July/Month

  1. Do you ever blog about S Hemisphere weather? I ask because I follow a WP blog called oceanicexplorer, which is from Australia, and today it’s got me thinking that we in the N Hemisphere may not be the only ones getting weird weather.

    • Unfortunately, I don’t usually blog about S. Hemispheric weather. The exception is the state of sea ice around Antarctica and the occasional major scientific study dealing with Antarctica itself. I know Australia suffered under extreme drought conditions through the 2000s, which got very little publicity. They also saw massive flooding in a couple of different episodes within the past year or so. I agree that increasingly anomalous conditions are not confined to weird weather.
      Thanks for the heads-up – I’ll go look for oceanicexplorer!

  2. Reading your blog from St.Petersburg, Russia.
    Today we have around 96°F (34°C).
    The first difference to Denver is that we are much higher in latitude: around 60°. The second difference is that we are much lower in altitude – around 3-5m above the sea level. That means that if more Greenland and Antarctic ice melts – there is no more St.Petersburg in its normal shape.Most likely I am not going to see it, but my kids will.

    • Good grief, that’s warm for 60°N! How anomalous is that temperature – does St. Petersburg see many 90°F+ (or 30°C+) days in summer?
      I didn’t realize St. Petersburg’s altitude was so low. I think you’re correct: by the end of the century, the population in that area will have to do something about rising sea levels. Is there any discussion of such adaptation measures at this time?

  3. To be correct, 34°C=93°F, though not a big difference. The previous two years were also abnormally hot, but 90°F+ we have only in the peak days. Can’t tell for sure – may be 3-5 days through the summer.
    In fact, there is no discussion at all. During the last 30 years they have built only a protection against occasional floods, when a wave comes from the Baltic sea for several hours. The rise of 2+ meters is annoying, 3+ – disastrous.
    That protection would not work against the permanent growth of sea level: we have a big river Neva that has no other way to the sea. May be there is a way to build a channel from the lake to the Gulf – about 40 miles long, and close the river, add some huge pumps…
    I heard of the future melting of Arctic ice – it would open new opportunities to get the oil from the sea shelf. Nothing is spoken about the methane emission, etc. And it was really surprise for me that the sea Ice can disappear by Spetember 2014th or 2015th. And then it could be the Greenland ice turn to melt.

  4. Pingback: Hottest July on Record for Denver, CO « Weatherdem’s Weblog

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