Summer 2004 Review For Southeast Lower Michigan
(Including an Outlook Into Autumn)

Written by: William R. Deedler, Weather Historian
National Weather Service Detroit/Pontiac, MI
September 10th, 2004

Additional section added 9/21/2004:
The First Day Of Summer, Correction, Fall, Will Be What The First Day Of Summer Should Have Been

Quick jumps on this page:

Note: Dark red and italicized text is taken directly from the 2004 Summer Outlook issued June 1st, 2004.

The Summer of 2004 will definitely go down as one of the cooler summers in recent memory across Southeast Lower Michigan. While we did experience some warm (even a few hot) summer days over the region, there were nearly as many cool, fall-like days to match. Each summer month (June, July, August) averaged below normal at the three major climate stations (Detroit, Flint and Saginaw) in Southeast Lower Michigan. Several outstanding things accompanied the cool summer weather: its persistence, its strength and its timing. The following Fig-1 lists the standard facts and figures for the summer months at Detroit, Flint and Saginaw. Strangely enough, with all the cool weather this summer, many are surprised to find out Detroit, with a summer average temperature of 69.1, never even placed in the top 20 coolest summers. The 69.1 degree average just missed the 20th position /68.9-1967/ by two tenths of a degree. Perhaps it is more than just a bit of co-incidence that the summer of 1967 pops up here (keep a watch out for it, and others, in this report). Arguably, the main reason Detroit did not place in the top 20 coolest summers list is, in two words, heat island. Overnight lows are mainly affected by heat island around cities and several overnight lows, like any month, were warmer at Detroit Metro than surrounding areas. There is strong evidence with the building and expansion of the Detroit Metro area (not to mention at the airport, itself) the urban heat island has spread out somewhat and frequently encompasses Metro Airport. The four degree difference in summer average temperatures between the NWS at White Lake and the Detroit Metro Airport may also reflect that somewhat, along with the obvious higher elevation and further north location of White Lake.

At Flint and Saginaw, where heat islands are little, if any problem, both cities placed well up in the top 20 coolest summers list. At Flint, with an average temperature of 66.7 degrees, a fifth spot placement was achieved (but just barely). In our top 20 listings for season temperatures, the average temperature is carried out to the hundredths for a more accurate placement. Flint's average temperature this summer came to 66.66 (rounded off - 66.7) which just placed this summer in front of the summer of 1985 which had an average of 66.70. At Saginaw, with an average temperature of 66.40 /66.4/ this summer, placed in ninth place for coolest summers.

                            SUMMER 2004 STATISTICS                
LOCATION….....JUNE..........JULY.........AUGUST......SUMMER.......SUMMER NORMS
          Temp / Pcpn   Temp / Pcpn   Temp / Pcpn   Temp / Pcpn   Temp / Pcpn
Detroit   67.1 / 2.86   71.8 / 2.85   68.5 / 4.52   69.1 / 10.23  71.4 / 9.81 
Depart    -1.9 / -.69   -1.7 /- .31   -3.3 /+1.42   -2.3 / + .42     
Flint     66.0 / 2.63   68.4 / 3.78   65.6 / 2.96   66.7 /  9.37  68.4 / 9.67
Depart    - .2 / -.44   -2.2 /+ .61   -2.9 / -.47   -1.7 / - .30  
Saginaw   65.1 / 2.97   68.5 / 1.14   65.6 / 2.37   66.4 /  6.48  68.9 / 8.94 
Depart    -1.7 / -.09   -2.7 /-1.36   -3.1 /-1.01   -2.5 / -2.46 
White Lk  63.4 / 3.94   67.5 / 5.43   64.4 / 2.94   65.1 / 12.31               
             (Departures based on standard 1971-2000 30yr norms)                 


Glancing up at Fig-1 and down at Fig-2 gives one an idea how persistent the cool weather was during the entire summer. Not only did all three summer months average below normal at all stations, but the number of days below normal each month was fairly consistent with about two-thirds of each month, below normal. Reviewing the Temperatures through the summer, it could be said that the "summer" was frequently like two seasons, summer and fall, interchanging one another. Checking out the below normal temperature days for each month and Summer 2004 total does help to confirm that, note that each month contained a majority of below normal daily departures, rather than normal or above normal days. Occasionally these below normal departures were extraordinary large (sometimes, 10-15 degrees below normal) for a summer day.

             Below Normal Days and Percentage of the summer 
             June   July   August   7/23-8/22      Summer   
Detroit       19     19      23     28/31=90%    61/92= 66%
Flint         17     19      22     27/31=87%    58/92= 63%
Saginaw       18     18      22     27/31=87%    58/92= 63% 

Perhaps nowhere was strength of the cold air intrusions more represented than the mid July to Mid August time-frame when normally, some of the warmest and nicest summer weather occurs (or one could say, at the "heart of summer"). Looking more specifically at the intra-month time period of July 23rd - August 22nd reveals some chilly facts for this heart of summer. All of Southeast Lower Michigan saw nearly continuous below normal days for that intra-month period! Detroit registered 28 out of 31 days that were below normal, and Flint and Saginaw, 27 days! This is noteworthy for a winter season but for a summer, it's exceptional. The average temperature at Detroit during this period came to 67.6 degrees, about six degrees below the normal /73.5/ for that time period. In fact, the remainder of Southeast Lower Michigan averaged about 5 - 7 degrees below normal for the same time-period!

The last time a summer was as cool or cooler than this summer across Southeast Michigan on the whole was back in the "Cold Summer of 1992". The average 1992 summer temperature in Detroit came in at an even 67.0 degrees which made it the second coldest summer on record since 1870. A 65.4 degree average made it the coldest summer on record since 1942 in Flint and an average temperature of 65.1 placed Saginaw in second place for coldest summer. The Summer of 1992 aside, this past summer actually had more in common with last summer, especially regarding general patterns and upper flow. Note last summer's pattern description written in the Summer of 2003 Review:

"The Summer of 2003 was relatively short but a nice summer in Southeast Lower Michigan. It seemed like it took forever to get going and then when some hot summer days would arrive, the overall progressive upper air pattern would usher in another cold front, knocking temperatures back down. One of results of this progressive upper air pattern was an active storm track which frequently produced heavy convective rains at several locations sometime during the summer".

Basically, this weather pattern description held true this past summer except this summer's cool air masses were more aggressive, especially in August which was considerably cooler than normal. This past summer had some stronger cold fronts that brought fall-like but still refreshing temperatures (sometimes for days after), especially in that mid July into mid August period when ironically, we usually have our warmest weather. Rather than growing weaker as the summer aged, some of these cold outbreaks remained unusually strong for the mid July to mid August time-period. The coldest of these air masses originated as far north as the Arctic, with their original strength and cold more typical of mid fall. Several days saw temperature rise only into the mid 60s to mid 70s, which are normals for mid September to mid October across Southeast Lower Michigan. These fall-like air masses were directed unusually far south by unseasonably large and deep upper low pressure systems over Eastern Canada.

The chilly mid-late summer period also reveals itself by way of the scarceness of 90s. Only three 90 degree or better days were felt in Detroit (for those who like a cooler summer, whose complaining?) with just one at both Flint and Saginaw. The 90s occurred at all three locations early in June, and again in mid July at Detroit, just before the cool down.

Reviewing the below normal temperature days for each month and the Summer as a whole, just underlines the cool summer. Note that each month contained a majority of below normal departures rather than above (or even normal) days. Occasionally, these below normal departures were extraordinary large (some 10-15 degrees below normal) for the summer day.


It should be stressed, again, that though the summer was cool, it still contained many delightfully pleasant sunny days with highs in the 70s and 80s and relatively low humidity’s. Still, there were enough contenders for miserable summer days also and one in particular stands out, July 27th.

Not only did the high temperatures fail to rise above the lower to mid 60s, but many of those highs occurred in darkness, after midnight in the early morning hours of the 27th! Now, while this does occasionally occur during the colder months of the year, this is a rare bird indeed for a summer day, especially in the peak of summer, in late July! During the afternoon of the 27th, as a chilly steady rain fell and stiff northeast breeze blew, temperatures hovered between the mid 50s to around 60. To show how rare it is to have 50s during a July afternoon in Southeast Lower Michigan, never at Detroit has a record low maximum temperature been below 60 during July. In other words, high temperatures have always hit 60 or better in Detroit since 1870 /134 years/ in July but that almost changed this July. The same holds for Flint, with the exception of one record day (7/14/67-58 deg) when the temperature failed to rise above 60.

The steady, sometimes heavy, cool rainfall left over an inch at many locations in extreme Southeast Michigan (or south of a Flint – Lapeer - Port Huron line to the Ohio Border). Comparatively speaking, that late July's afternoon weather was more typical of late October or early November, not the height of the summer.


While on the subject of cool afternoons, this is a good time to list /Fig-3/ the daily record low maximums and the record lows that occurred during the summer. Also, believe or not, there was actually one record high this past summer, on June 8th at Flint with its only 90 degree day of the summer.

Detroit                       *M64 / 27th

Flint        H90 /  8th        M65 /  8th     M64 / 11th
                               M72 / 24th     L43 / 22nd
                               M63 / 27th     
Saginaw      L42 / 25th                       L43 / 15th

M=Record Low Maximum (N/A for Saginaw)
H=Record High
L=Record Low
* Afternoon high was only 62

Also, Looking back at the number of 60s, 70s, 80s and 90s during June through August in Detroit, Flint and Saginaw reveals the following:

Number of Days in Detroit/Flint/Saginaw with temperatures in the:

Temps     June         July       August     Summer       Norm  Days
        D/ F/ S      D/ F/ S      D/ F/ S     D/ F/ S 
60s -   4/ 5/ 7      1/ 2/ 2      1/ 6/ 5     6/13/14     
70s -  15/13/13     10/13/12     19/18/16    34/44/41    
80s -   9/11/ 9     19/16/17     11/ 7/10    39/34/36     40/-/-
90s -   2/ 1/ 1      1/ 0/ 0      0/ 0/ 0     3/ 1/ 1     12/7/7

At Detroit, while there were many 80 degree days, almost normal /40/ with a total of 39 days. As far as 90 degree days, however, they were almost non-existent with just 3 days this summer at Detroit and only one at both Flint and Saginaw. Generally, Detroit has about 12 days of 90 degrees or higher for the year, while Flint and Saginaw have about 7. Therefore, the lack of 90s, not 80s, was the trend seen during the summer. Since we totaled near the normal amount of 80s, we basically traded 90s for an increase in 70s and 60s.


If it seems like to you there have been more thunderstorms and severe weather the past few years you are right. The thunderstorm numbers for both years, up through August, indicate both years superseded the annual normal of 33 by the end of August. Also like last year, this severe weather season was again active, especially early-mid season. An active storm track brought several rounds of thunderstorms this past spring right into summer. May was the particularly active severe weather month this year, containing several rounds of severe thunderstorms which brought damaging winds, record rainfalls (and subsequent flooding) along with isolated tornadoes. In fact, there were 14 days that contained thunderstorms in May alone which broke the old record for May thunderstorms days /11-1896/. Before May, however, one had to look way back to July 1902 and June 1892 to find a month with 14 days of thunderstorms. Therefore, it took over a century /102 yrs/ to again record 14 days of thunderstorms in a month. So, by logical deduction, there is yet to be a month containing 15 days of thunderstorms in Detroit since the record months of May /2004/, June /1892/, July /1902/ all contained 14. It is also interesting to note that just last August /2003/, 12 storm days were recorded, while not a record for August /13-1876/, it was the first time August had that many storm days since 1947!

                       STORMY YEARS - BACK TO BACK        ANNUAL
2003      3     3     5     5     8     12     36           33
2004      1     2    14     7     6     10     40           33

Records going back to 1871 indicate normally we see on average 33 days with thunderstorms for the entire YEAR! The record amount of thunderstorm days for an entire year occurred back in 1917 with a whopping 53 days of storms. While last year was rather stormy, this year has already superseded that with 40 storm days (as opposed to 36 at the end of last August). The total amount of storm days in 2003 came to 44 by years end...plenty, but still 9 shy of the record.

These rounds of storms this season, frequently intensified into severe limits and resulted in numerous severe weather warnings. In fact, since warnings began at DTX /1995/ with the inception of the 88-D Doppler Radar, the 2004 severe weather season has produced the most warnings issued in a season already, with the 2000 season now number two. In addition, last year (2003 season) we set an all-time record for severe weather events with 199 reports of severe weather. Guess what? That record has now been broken for the second year in a row with the current severe weather season having 222 reports of severe weather through August.


Like most summers, rainfall across Southeast Lower Michigan varied depending on location. Most areas, however, seemed to have sufficient rain through the summer with maybe a dry spell or two, especially in July into mid August. Drier conditions were most notable in the Saginaw Valley and Thumb Region during July into early August. Saginaw reported just over an inch /1.14"/ of rain in July, while most other areas in Southeast Lower Michigan received 2 - 3 inches.


Some Monthly/Summer Rainfall Amounts from Southeast Lower Michigan
Detroit /DTW/          Wayne        2.86    2.85    4.52       10.23
Flint   /FNT/          Genesee      2.63    3.78    2.96        9.37
Saginaw /MBS/          Saginaw      2.97    1.14    2.37        6.48 
White Lake /DTX/       Oakland      3.94    5.43    2.94       12.31 


When comparisons were drawn with last winter's successful parallels (winters researched for the Winter 2003-04 Outlook) and recent spring trends, the following forecast for Summer of 2004 was stated in the Summer Outlook:


“While the data reviewed is extremely variable, look for temperatures to average around normal to above normal. This is not to say there will not be intermittent cool periods during the summer as the upper wind flow occasionally backs to the northwest. In fact, of particular concern is the persistently cool and aggressive upper air pattern that continues to hold over Eastern Canada with only some weakening likely. At the same time, however, strong ridging across the southern/central U.S. should routinely push heat and humidity back into the area. In the end, it is expected that the above normal temperatures will at least offset the below normal temperatures, leading to the near normal to above normal readings”.

What Happened to the Heat?

Ironically, the above pattern expected for the summer was observed but the aggressive cool upper wind pattern over Eastern Canada remained unusually strong, especially in August, which was even more atypical. The summer upper air ridging pattern and resultant heat mentioned above, was very evident over the Southwest and Southern Plains but it was not strong enough to offset the predominance of the unseasonably cool (several times of Polar origin) air invading the Lakes Region from Canada. While the expected upper air pattern materialized, being "sandwiched" between the two upper air features meant any subtle deviation of either would cause a substantial influencing pattern change. In the case of this summer over Southeast Lower Michigan, the stronger and colder upper low pressure system over Eastern Canada was basically responsible for the cooler than expected summer.


"The pattern of relatively tranquil weather followed by a notably wet and stormy period that commenced last winter has persisted strongly into the spring. This was evidenced recently by one of the driest Aprils on record being followed by the wettest and stormiest Mays! Overall, this pattern is expected to persist into the summer but hopefully not as extreme. Therefore, while significant dry and wet periods will persist, it is felt that overall, rainfall will average near normal to above. Several of the springs - summers researched displayed this feast/famine rainfall pattern. Because of the extreme variability found with the summer storm patterns, areas with below normal rainfall would not all be a surprise either."

Variability is what the research expected, and variability is what we got. This worked well over the entire region. We indeed had most areas seeing near normal to above normal rain, but portions of the Saginaw Valley and Thumb Region had locally deficit rainfall. Nearer the extremes, bouts of heavy rain this summer pushed White Lake's total over a foot /12.31"/ for the summer, while at the same time, Saginaw reported about half that amount with under 6 1/2" /6.48/.

Like most summers, rainfall across Southeast Lower Michigan varied depending on ones location. Most areas, however, seemed to have sufficient rain through the summer with maybe a dry spell or two, in July or August. Along with the majority of the region seeing normal to above normal rainfall, our monthly summer guidance for the Detroit area suggested August had the best chance to be the wettest month, which it was with over 4 1/2".


Below are the summers that were selected and referenced for the summer outlook issued June 1st

Figure - 6


 Temp/ PcpnTemp/ PcpnTemp/ PcpnTemp/ Pcpn 
30 Year
71.4/ 9.8169.0/ 3.5573.5/ 3.1671.8/ 3.10 
100 Year
71.0/ 9.50 

Summer ofTemp/ PcpnTemp/ PcpnTemp/ PcpnTemp/ PcpnOverall Summer
1901+ 72.5/10.78 +68.9/ 2.08-7- 76.8/ 5.50 (15)71.9/ 3.20/20th Warmest/
1920- 69.4/13.34 ++69.1/ 5.49 (11)69.7/ 3.6569.5/ 4.20/15th Wettest/
1933+ 74.0/ 5.90 ---1- 74.6/ 1.19 -8--18- 75.4/ 2.4772.0/ 2.24/4th Warmest/
/17th Driest/
1942+/- 71.1/ 9.78 +/-69.0/ 2.3173.6/ 3.3570.6/ 4.12 
1953+ 72.9/ 7.26 ---17- 70.9/ 3.0973.5/ 2.65-13- 74.3/ 1.52/15th warmest/
1959+ 73.5/ 9.35 +/-70.1/ 1.01 -3-74.1/ 1.27 -17--3- 76.3/ 7.07 (5)/9th Warmest/
1967- 68.9/ 9.09 -70.4/ 4.2369.0/ 2.85(8)67.3/ 2.01/20th Coolest/
1975+/- 71.2/12.20 ++69.0/ 2.3972.2/ 1.9872.3/ 7.83(2) 
1978- 69.8/ 6.39 --66.8/ 2.69(17)70.6/ 1.9771.9/ 1.73/20th Driest/
1979- 68.3/11.99 ++66.6/ 4.04(14)70.4/ 4.96(13)67.9/ 2.99/13th Coolest/
1981- 70.1/ 9.94 +/-68.0/ 3.3372.4/ 4.2970.0/ 2.32 
1993+ 72.5/ 9.82 +/-67.5/ 6.05 (8)-17- 75.5/ 2.17-10- 74.5/ 1.60 
2001+ 72.4/ 7.49 --69.6/ 3.4173.6/ 1.16 -11--15- 74.1/ 2.92/Just Below
20th Warmest/

Mean:71.3/ 9.5269.3/ 3.2172.8/ 2.9471.7/ 3.37 
(  ) Monthly Coldest or Wettest Ranking
-  - Monthly Warmest or Driest Ranking
+   above normal++ well above (2.00"+)
-   below normal-- well below (2.00"+)
+/- normal (within .5 degree or .50" precipitation)

The following was stated in the outlook:

“Reverting back to the winters that contained some similar traits to this past winter (1958-59, 1966-67, 1978-79, 1980-81 and 2001-01) and a bit of temperature trend evolves for the summer. Three out of the five summers: 1967, 1979, 1981 all contained cooler than normal temperatures. Therefore, does this help tip the scales toward a cooler than on average summer? This, of course, is assuming the overall cooler than normal trend hasn't changed - or has it? Reviewing more recent surface and upper air data/trends from the spring /Mar-May/ argues it has and suggests a warmer pattern of above normal temperatures may be in the works”.

As it turned out, the best indicator for the summer was indeed the trend suggested by the previous winters (and trend that is normally followed and given more credence in this study) along with the residing upper air pattern. The assumption (or error) made was putting too much faith into what turned out to be a "temporary" upper wind change, even though the above normal temperature pattern did persist for about three months. Looking a bit closer at the chosen and more anomalous winters and subsequent summers of 1967, 1979, 1981 shows that these three summer trends had a very good handle on what this summer would be like. Not only the below normal temperatures but the near normal to above normal rainfall! In fact, in regard to temperature, the summer's average temperature of 69.1 just missed tying the 20th coolest summer spot by two tenths of a degree /.2/! Again, had it not been for the general heat island around Detroit in the present, a placement further up in the top 20 coldest summers list with 1967 or 1979, would have been assured. Actually we had a fourth summer that was similar (or anomalous) to the Summer of 2004 and that was the Summer of 1920. While it was wetter at Detroit in 1920 (but remember now, White Lake did have quite a bit more rain than Detroit with 12.31") the summer mean /69.4/ was, like 1981, just a bit warmer.


DETROIT      SUMMER          June            July          August
Summer    Temp / Pcpn                                                  Overall Summer
1920    - 69.4 /13.34 ++  69.1 / 5.49(11)  69.7 / 3.65   69.5 / 4.20   /15th Wettest/
1967    - 68.9 / 9.09 -   70.4 / 4.23      69.0 / 2.85   67.3 / 2.01   /20th Coolest/ *
1979    - 68.3 /11.99 +   66.6 / 4.04      70.4 / 4.96   67.9 / 2.99   /13th Coolest/ *
1981    - 70.1 / 9.94 +/- 68.0 / 3.33      72.4 / 4.29   70.0 / 2.32

2004    - 69.1 /10.23 +   67.1 / 2.86      71.8 / 2.85   68.5 / 4.52

-   Below normal
+/- Near Normal
+   Above normal
++  Well Above

Autumn Trends and Outlook:

Like the past several seasons, with the lack of any significant El Nino or La Nina, the trend for the upcoming fall season is more variable and less discernable. Despite this lack of influence, there are other patterns to research.

As with recent seasonal research, the wide variability in the autumn periods, ironically (or maybe not) lead to an average temperature within a half degree or so of the normal. There were some notable wide ranges in temperature and rainfall amounts found in particular years, as the saying goes, the averages are the sum of the extremes. Note the following (all data is in reference to Detroit):

September normal... 63.9
October normal... 51.9
November normal... 40.7
Autumn Average... 52.2 !
13 Septembers researched... 63.6
13 Octobers researched... 52.5
13 Novembers researched... 40.4
13 Autumns Average... 52.2 !

The above stats, however, do not tell the story at all, as monthly temperature ranges were incredible, some as much as 10 to 12 degrees. The same thing can be said about the precipitation, especially seasonal totals. Precipitation totals varied from as much as 13.39" as recent as 2001 to over ten inches less with 3.26" in 1953 (talk about a range)! In this case and, as the saying goes, the averages are the sum of the extremes.

Emerging Patterns in the Rough?

Since there such a range in our data, it is best to look at present trends, upper wind patterns and best past performance. The best past performance brings up our recent summer list of years, 1920, 1967, 1979 and 1981 and comparing that to our present pattern.

DETROIT      Autumn         September      October      November
Summer    Temp / Pcpn
1920    + 54.8 / 5.92 -    65.7 / 1.37   59.5 / 2.26   39.1 / 2.29
1967    - 48.8 / 9.60 +    60.4 / 1.96   50.7 / 4.87   35.2 / 2.77
1979    - 50.7 / 6.37 -    62.6 / 0.94   50.1 / 1.24   39.5 / 4.19
1981    - 49.9 /10.65 +    60.9 / 5.47   47.6 / 3.92   41.1 / 1.26
Ave     - 51.1 / 8.14 +/-  62.4 / 2.44   52.0 / 3.07   38.7 / 2.63
Norm      52.2 / 8.16      63.9 / 3.27   51.9 / 2.23   40.7 / 2.66

September into early October:

The 13 Autumns, along with 4 best performance summers (above) and most importantly, recent trends, indicate the early fall weather will have temperatures average generally above normal, while rainfall averages normal to below normal (minus any hurricane remnants). Look for any cool air masses (or below normal temperatures during September into early October), to moderate fairly quickly with temperatures returning to normal or above. Interestingly, none of the September's averaged within a half degree of normal, the stats indicate either it would be above normal or below. In fact, out of the three months, September had the best chance of the autumn months for temperatures to average above normal with six out of the original 13 research autumns above normal - with three of those six substantially above (2-5 degrees)!

October into November:

As mid October approaches. look for upper air/weather pattern to once again become more turbulent with more aggressive cold air masses, resulting temperatures averaging around normal to below. Killing Frost/Freezes look to be around their average dates. Similar to last fall, the chances for an Indian Summer or two, look better than average, coming after the killing frost.

October, specifically, contained a mix of data but was strongly indicated to be our transition month (which is normal) but with the overall temperature trend toward normal to below. The timing of the "fall-parade" of cooler air-masses from Canada during the month will ultimately dictate the resultant average temperature. A large number, (ten out of 13 years), indicated normal to below normal temperatures (5 years each).

November's proved to have the best chance to average below normal with six years below normal, four near normal and only three, above normal. Also (and similar to last year), the risk of an early or above normal snowfall is noted mid to late fall. We shall see.

In any event, it looks like there will ample time to enjoy the autumn weather in the next month or two, so make the most of it!

Dates of Interests for the Autumn (all data based on Detroit data base):

Autumn arrives all areas: September 22nd at 1230 pm EDT
Average date of the first killing frost/freeze (not light frost): October 21st
Earliest killing frost/freeze in Detroit: September 22nd, 1974
Average first date of snow (Trace): Approximately Halloween (or last week of October)
Earliest appearance of snow recorded in Detroit (Trace): October 1st, 1974 is the U.S. government's official web portal to all federal, state and local government web resources and services.