So I know this is more just Front Page-related that car-related, but I sort of fell into a bit of a wormhole on weather data in Phoenix, AZ after seeing the article on Jalopnik and I wanted to share some of what I found.

Lets start with the question: Is it normal for it to be 119°F in Phoenix? In a word, no. While it may get even hotter than that out in the desert, the fact is 119 is the fourth highest temperature ever recorded in Phoenix. Now, to preface the following averages, I was looking at the last 20 years of data, so 1997 to 2017. The average temperature for the entire month of June in Phoenix is a balmy 91.7 degrees. Of course that doesn’t tell the whole story because it includes the temperate a night and spikes during the day and averages it all out. Now, the average daily high for the month of June is a toasty 104.5°. That may seem hot to most of us, but a 119 degree day is not only one of the hottest on record, it’s also 15 degrees hotter than the average high temp for a day in Phoenix in June. So this was nearly a record-setting day and is certainly way above average.


But what about very hot days in general, how uncommon are they? Well, there are two answers to the question and they depend on whether you mean historically or recently. Of all the years between 1895 and 2017, in thirty-three of those years has a temperature greater than 115°F been recorded. This suggests that about one in every four years the temperature exceeds that, and usually then for only one day. Again, this statistic would mean a day over 115 is quite uncommon occurance, especially considering that most days in June or July it doesn’t pass 105.

However, 15 of those years on record with these high temps were between 1987 and now. This means that in the last 30 years, half have seen the temperature exceed 115° at least once. Moreover, 8 of the last 10 years have seen temperatures reach that high, including every year since 2011. So while it is not normal for any one day to be that hot in Phoenix, it is increasingly common.

Looking more into it, in most years with a recorded temperature that high, it is usually only on one day. Years with two or more days recording over 115° include 1989, 1990, 1994, 1995, 1998, 2003, 2006, 2011, 2013, 2016, and 2017. Meanwhile, there are only 3 years with more than one day over that temp in the near 100 years of records before that.

Also incase you were wondering, the hottest day on record was June 26 1990 at a scalding 122°F.


Also this is almost unrelated, but someone also asked the hottest nights (the max lowest temp for any given 24 hour period) in Phoenix, so I dug info up on that as well. From my comment:

So it seems like average maximum low temperature taking every year from 2000-2017 is 93. So basically the lowest temp recorded on the hottest night of each year from 2000-2017 averages to 93. The hottest low on record was July 15, 2003 and the lowest temp for that day was 96°F! There isn’t any record from 1900-2017 of the overnight low ever being over 100 degrees.

Now I’m sure it’s maybe hotter or colder than that out in dessert or at an some random air force base or something, but this is just in Phoenix we’re talking here.

Now more interstingly, when you factor in historical data, it does paint a picture of very hot nights being increasingly more common and hotter than ever. The average hottest low temp per year from 1900 to 1999 is only 87 degrees, so 6 degrees cooler than the average for the hottest nights in the last 17 years! A year with a nightly low over 90° used to come around only once per decade for most of the 20th century, but now its done that every year since 1991. What was once an extreme oddity, a night where it never drops below 90° in Phoenix, is now something that happens up to several times every year.


I don’t know if any of you found this as interesting as I did, but I’m still playing with the weather data. Usually with climate science its hard to see change in maximum and minimum temperature data because it can be all over the place, so I guess it can be interesting to be able to identify trends in anything but slowly moving averages. I’m sure a full statistical analysis could be done on the hottest days and hottest nights in Phoenix, but I’ve already spent enough time just casually perusing the data. Since I picked a specific cutoff for my “very hot day” criteria, that method of selection isn’t entirely statistically sound. If someone is insistent on analyzing hottest days by year, what would be better is if the yearly max temps were placed on a bell curve (just glancing at the data I’m sure it’s some multiple of a standard deviation) and the deviations of more recent years were compared to every historical hottest day. I’m not going to take the time to do that...also the raw data from the source I was using isn’t downloadable as an excel spreadsheet.

Full disclaimer, I suppose I’m not technically a scientist and I’m definitely not a climate scientist. It’s safe to say I knew what I was doing and I knew what I wasn’t doing though.


Here’s the source for everything:

And here’s some very, very hot Lamborghini exhaust flames:

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