July 2011 in the Running for One of the Hottest...If Not THE Hottest...Month in Detroit ! t!

With just a few more days to go, July 2011 is shaping up to be THE hottest month in recent memory across Southeast Lower Michigan and one of the hottest, if not THE hottest, on record (depending on location and records).  As you can see by the table below, Detroit hottest month is shared by July from two different years: 79.0 degrees in both 1955 and 1921.  Flint's hottest month on record comes in at 78.0 degrees, also back in 1921, while Saginaw is at 77.5 in again, 1921.  So basically, the hot July of 1921 is the beast to beat at all three sites.  Ironically, this is nearly a century ago and not in recent records (something to think about).  It just adds credence to statement I've made several times in the past when the media or general public say, "this has never happened before" or "this is unprecedented"!  Most of the time, I just answer:  "yes it has" (or something close to it).  This, along with interest and fascination on my part, are the reasons I wrote so many articles on weather history and events in Southeast Michigan...to satisfy that curiosity.

Back to 1921,  the urban expansion and heat island at Detroit was much less than in 1955 or today.  Still, was it enough to influence the temperatures since Detroit's climatological station was downtown in the City?  Probably a bit, but a check of overnight lows and daily temperature ranges that month (compared to Flint and Saginaw) would clear the picture some.  What is needed is a comparison of July's highs and lows for both 1921 (and let's not forget 1955) with this year (and I don't have the detailed data in front of me).  An educated assumption on my part is that Detroit's climate back in 1955 had more of a urban influence than 1921 since as it was still downtown (at DET, Detroit City Airport) and there was quite the urban sprawl between 1921 and 1955. Even stronger evidence for some urban heat influence back in 1955 at Detroit is that both Flint and Saginaw placed lower that month in 4th and  5th place, respectively (see below) for hottest month.  The most important fact is that July of 1921 comes up as the hottest month at all three sites, strong verification it was"THE" hottest of times in old Southeast Michigan

Another important fact (especially with public perception) is what type of heat engulfed the region in both 1955 and 1921? Were they hot and humid months or hot but somewhat "drier air months" (so to speak, meaning less humidity and similar to that of June of 1988). The dew points and subsequent humidities along with overnight lows in both months would tell the story. If one or both were a "drier air months", the residents of Southeast Michigan would at least get some relief from the heat, especially at night.  In addition, did the drier trend prevail or was it only a few nights.

In any event, when just comparing apples to apples (temperatures), July of 2011 is fast going to down in climate history books as the record or near record hot month. This will depend on what happens between now and the end of the month (which looks to be accommodating with more heat and above normal temperatures).

Detroit as of 7/25/11 has an average temperature of 79.5 /79.0-1955 & 1921 record/ and thus, now sits in first place for hottest month!  The average high temperature for July thus far is an incredible 89.6 /90/ degrees while the average low is sitting at 69.3 degrees.  Flint is averaging an even 77.0 degrees /3rd-place, 78.0-1921 record/  for hottest month.  Flint's average high is nearly as hot as Detroit with 89.2 but with a substantially cooler average low coming in at 64.8 degrees (4 1/2 degrees lower than Detroit).  This could be the result of a number of factors: the lack of urban heat influence (it's still relatively rural around the site) along with cloud cover and rainfall.  Detroit has been notably wetter than Flint up to this point with 3.23" falling at Detroit compared to Flint's meager .45" (and this would, at times, tend to inhibit overnight lows from falling as much at Detroit).  Finally at Saginaw with an average temperature of 76.3 degrees /3rd-place, 77.5-1921/ and an average high of 86.6 and low of 66.0 (note, a bit higher than Flint) is also sitting at the 3rd hottest month, thus far.  

Stay Tuned.

Rank Detroit Area* Flint Bishop** Saginaw Area***
Coldest Warmest Coldest Warmest Coldest Warmest
Temp Year Temp Year Temp Year Temp Year Temp Year Temp Year
1 12.2 Feb-1875 79.0 Jul-1955 10.9 Jan-1977 78.0 Jul-1921 9.4 Jan-1912 77.5 Jul-1921
2 12.8 Jan-1977 79.0 Jul-1921 12.8 Feb-1979 77.7 Jul-1935 10.4 Jan-1918 76.8 Jul-1916
3 13.1 Jan-1912 77.9 Jul-1916 13.1 Jan-1963 76.7 Jul-1934 11.6 Jan-1963 76.2 Jul-1935
4 13.2 Jan-1918 77.7 Jul-1931 13.4 Feb-1978 76.5 Jul-1955 11.7 Feb-1904 76.0 Jul-1931
5 14.8 Feb-1934 77.1 Aug-1995 13.8 Jan-1994 76.1 Jul-1931 12.1 Jan-1994 75.9 Jul-1955


  1. Update!!
    Preliminary average temp for Detroit in July 2011 is 79.3 degrees and this makes July 2011 the hottest July and MONTH on record (see earlier write up above).

    Also we had 14 days it reached 90 degrees or better. This was NOT the record for July. That honor belongs to July of 1955 with 17 days of 90 or better. We now have a three-way tie for second place for the number of 90s+ in July with 14 days. July 2011 ties with July of 1977 and 1934. By the way, back in that July of 1977 we had a July monthly max of 102 (one of two 100s in the month). The Summer of '77 followed the brutal winter of 1976-77.

    It also was the second wettest July on record at Detroit with
    7.66" (second to 1878 with 8.76").

  2. The similarities between July 1955 and 2011 were uncanny temp-wise. The only notable difference that July 1955 is the 9th driest July (1.10") and July 2011 is the 2nd wettest (7.66"). (Had a whopping 8.77" in Wyandotte in July, my wettest month since I started records in 2000).

    ................JULY 1955...........JULY 2011
    Avg temp..........79.1.................79.3
    Avg high...........89.6.................89.3
    Avg low............68.5.................69.3
    85F+ days.........27....................27
    high 89F days.....3......................6
    90F+ days........17....................14
    95F+ days.........5......................5
    100F days.........1......................1
    low 70F+ days....17...................15
    low 75F+ days....2......................4