Don't Panic! You'd Never Know it by the Weather But Climatological Summer is Already Half Over; Now What about the Second Half?

The first six weeks of summer are in the books (and you couldn't prove it by me) but where have been all the typical hot days of summer? Even though June averaged around normal; the notably cool July thus far with temperatures averaging 2 - 4 degrees below normal has certainly taken a bite out of the heat! In addition, only ONE 90 degree day has been officially registered at Detroit - in June no less; (none, officially at Flint nor Saginaw). This has made it seem like we have been in a perpetual June pattern for weeks, not dead-center summer or what if typically called the Dog Days of summer.

"Dog Days of summer is the name for the most sultry period of summer, from about July 3 to Aug. 11. Named in early times by observers in countries bordering the Mediterranean, the period was reckoned as extending from 20 days before to 20 days after the conjunction of Sirius (the dog star) and the sun."

The expected upper wind pattern across the country discussed in the Summer Outlook has verified extremely well for the first half of the summer with the two moderately strong jets (Polar and Pacific) occasionally phasing and vying for dominance.

A good example of the prevailing jets expected this summer (see further below); also shows on the map below, taken from a recent model prog panel. Note the persistent oscillating North American pattern thus far this summer (as described in the Summer Outlook). The Pacific jet continues sending shortwaves into the mid part of the country, which flatten the summer ridge only to occasionally phase with the Polar short waves digging south into the eastern half of the country. There has been no shortage of storms and severe weather this warm season where one, or both of these jets pass over the country. Though occasionally getting clipped with severe weather in Southeast Lower Michigan (most notable June 22-23rd), we have missed the bulk of the severe weather to a large extent as heat and humidity bubbles up across the Midwest and Ohio Valley; only to be shunted east many times just south of the Lakes Region. This has been courtesy of our friendly Polar Jet which also has made summer temperatures quite tolerable (see maps below). Looking ahead to the second half of the summer in this regard, I would expect the upper ridge to give more equal showing than the first half, providing Southeast Lower Michigan more summer-like temperatures and resulting storms. At the same time, the Polar jet shows she's here to stay; routinely visiting through the rest of summer.

From the Summer Outlook:

Summer 2015

Glancing at the upper wind projection for the Summer of 2013 show similarities to this summer and differences. The difference noted for this summer 2015 projection is the better subtropical jet projected and thus, a more variable upper ridge strength. This is a result of building and flattening ridging in response to short waves riding in and through the region from the west. This is depicted on both maps with the first a computer generated 500 Heights and my interpretation of active areas of surface patterns. The second map, my interpretation of summer dominant and placement of air masses. 


Broadening this summer discussion out a bit, the first half of summer (or the first six weeks); temperatures across Southeast Lower Michigan have averaged a "comfortable" 69 at Detroit; 68 1/2 at Flint and 68 at Saginaw. A quick average and rounding gives us an average for the first half of the summer of ~ 68 1/2. Delightful temperatures none-the-less if you like a comfortable summer; which is just so happens what the analogues called for in the Summer Outlook.

Analogues favor the cooler side of normal which seems reasonable considering upper wind patterns over Canada and El Nino trends. The analogue summers were extremely variable but with definite trends within with four cooler than normal, six normal and two warmer with a generally a comfortable summer projected. Not surprising, the average temperature while in the normal range, leaned a bit toward below normal - makes perfect sense with twice as many cooler than warmer summers. This is not surprising as El Nino Summers lean toward the cooler side of average. Also, the chances of long hot spells are less than average and subsequently; average to below average /8-12/ so too are the amount of 90 degree days.  

In defense of the summer weather thus far, looking at the actual statistics and norms it may also surprise you that even though the summer's been on the cool side, the summer hasn't been all that terribly cool, statistic-wise. While temperatures have averaged around 68 1/2 across the ENTIRE region, it's the departure from normal at Detroit which makes it seem much cooler. Detroit's normal are skewed UP about 1 1/2- 2 degrees higher than the normals at either Flint or Saginaw due to the heat island. June norms are as follows: 69.4/ 66.5/ 67.2 respectively and July normals include the following; 73.6/ 70.5/ 71.0 for Detroit, Flint and Saginaw. Those stats alone show the preference for a metro Detroit warmer heat island. Realistically speaking if no heat island existed at Detroit, the normal at Detroit IMHO should be only about a degree or so warmer than Flint and Saginaw.  Therefore; the average temperature across Southeast Lower Michigan for the first six weeks is running roughly a degree below normal when all three locations are averaged together and separately; Detroit ~ -2.2, Flint and Saginaw area ~0.4 degrees

If we briefly scan the 20 coolest summers list at all three locations and even if we continued to average right where we are now for the rest of the summer; only Detroit just nicks the top 20 list of all three locations. If we average just near normal the rest of the summer, temperature averages would rise some.

                                  Again Detroit's at about 69, Flint's 68 1/2 and Saginaw 68 thus far

                                  Top 20 Coldest/Warmest Summers in Southeast Lower Michigan

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 66.5 1915 74.8 2012 65.4 1992 74.2 1933 64.8 1915 73.0 1931
2 67.0 1992 74.8 2005 66.1 2009 74.0 1934 65.1 1992 72.9 1933
3 67.3 1927 74.5 1995 66.2 1958 72.7 1936 65.5 1982 72.5 1955
4 67.5 1875 74.5 1955 66.3 1960 72.6 1939 65.8 1945 72.3 1995
5 67.6 1903 74.4 2011 66.5 1969 72.6 1931 65.9 1950 72.1 1930
6 67.8 1985 74.4 2010 66.6 2004 72.6 1921 65.9 1924 72.1 1921
7 67.9 1912 74.2 1988 66.7 1985 72.3 2010 66.1 1985 72.0 2012
8 67.9 1907 74.0 1933 66.8 1972 72.3 1949 66.4 2009 72.0 2010
9 68.1 1982 73.8 1949 66.8 1967 72.2 1955 66.4 2004 72.0 1937
10 68.2 1972 73.7 1921 66.9 1962 72.0 1935 66.4 1979 71.9 1988
11 68.3 1979 73.6 1952 66.9 1927 71.9 2011 66.5 1977 71.9 1936
12 68.3 1902 73.5 1991 67.0 1982 71.9 1938 66.6 1951 71.7 1998
13 68.3 1891 73.5 1959 67.0 1950 71.8 1988 66.8 1946 71.5 1934
14 68.4 1889 73.5 2002 67.1 1965 71.7 2012 66.9 1965 71.5 1932
15 68.5 1883 73.5 1931 67.1 1945 71.7 1995 66.9 1962 71.4 2011
16 68.7 1917 73.2 1944 67.2 1997 71.7 2002 66.9 1917 71.4 1959
17 68.8 1924 73.0 1987 67.4 1951 71.7 1987 67.0 1958 71.2 1973
18 68.8 1904 73.0 1919 67.4 1957 71.6 2005 67.0 1926 71.2 1949
19 68.9 1967 72.9 1953 67.4 1924 71.6 1983 67.2 1972 71.2 1919
20 69.1 1897 72.9 1930 67.5 2000 71.3 1944 67.3 1981 70.9 2005
* Detroit Area temperature records date back to November 1874.
** Flint Bishop temperature records date back to January 1921.
*** Saginaw Area temperature records date back to January 1912.


Average Temperature Departure maps


 JULY 1-14


While heat has been lacking this summer thus far, rainfall has NOT; especially across the southern counties of Southeast Lower Michigan!


Location                                 Amount                                 Norm    Dep
Detroit:   SINCE JUN 1      6.25                      4.95   1.30
FLINT:    SINCE JUN 1      7.64                      4.44   3.20  
SAGINAW   SINCE JUN 1      5.74                      4.11   1.63

To maintain the integrity of my Summer Outlook; the second half of the summer should be drier across the Saginaw Valley and Thumb region while normal to above rainfall continues across the southern two thirds, since all areas are now above.



I look for rainfall to be quite variable as mixed data presents conflicting results and where and how much may also be exasperated more than what is typical for many summers. Taking all data (past and present) into account; rainfall is expected to be above normal over the southern sections of Southeast Lower Michigan and normal to possible even below across the Saginaw Valley and Thumb Region. As with temperatures, timing of the wettest and driest periods will be quite variable - not unlike the spring. 

Also; This is similar to 2013 where heavy amounts were seen over the south and lighter, below normal amounts were observed in the Saginaw Valley and Thumb.


Rainfall Totals Departure maps:

The wet June stands out like a sore thumb, a subtly drier pattern has begun to emerge in July - and mainly in the Thumb/Saginaw Valley region - BUT it is too early to call it a trend and we'll stick by the original forecast. I'll give my original summer forecast time to hopefully work out for all areas.


And with that, this brings me to my Outlook for the Remainder of the Summer

And, to that - little overall change to my original call with Temperatures averaging 1 1/2 below to 1 1/2 above normal while rainfall is above across the southern sections (Flint area to Port Huron south the Ohio border) and normal to below across the Saginaw Valley and Thumb Region. Most areas should see adequate rains this summer if past and future is any guide.

Temperatures overall (and this should balance out the first half some), I look for warmer temperatures on average with more normal to above normal the second half of the summer as upper ridging gains some ground - so don't count the summer out just yet!

Making weather fun while we all learn,
Bill Deedler -SEMI_WeatherHistorian


  1. I am really glad that I came across your blog. Its nice to have one dedicated to southeast Michigan. I'll be checking back often. Thanks.

  2. Thanks for your kind words. I started the blog just as I retired to keep the work I did while with the NWS, going. I received many encouraging kudos while with the NWS and notes like yours makes my time worthwhile in "retirement". lol!