Summer 2003 Review for Southeast Lower Michigan

Written by: William R. Deedler, Weather Historian
National Weather Service Detroit/Pontiac, MI
September, 2003

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Unless otherwise noted, dark red and italicized text is taken directly from the 2003 Summer Outlook issued in June, 2003.

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. It was not unusual to see an area get "dumped on" by storms in one week, only to be left "high and dry" weeks later. By nature, this "feast or famine" scenario is not atypical of convective season rains, it just seemed a bit more pronounced this past summer.

Stormy Weather

The active storm track brought several rounds of thunderstorms this spring right through summer with only the occasional break in the action. Through the end of August, 36 thunderstorm days were totaled up at Detroit Metro Airport so far this year. Records going back to1871 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 thunderstorms.

August was an exceptionally busy month in terms of number of thunderstorm days at Detroit. A total of 12 days in August had thunderstorms, well over twice the norm /5/ and just below the record for August (13 days - which occurred way back in 1877)! The 12 thunderstorm days tied with 1925 and 1947 for second place in August. So, August 1947 (56 years ago) was the last time 12 storm days for August (or any month for that matter) was seen. The record amount of storm days for any month is 14 which occurred back in July of 1892 and 1902.

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 /1994/ with the inception of the 88-D Doppler Radar, the 2003 severe weather season so far has produced the second most warnings issued in a season, with the 2000 season number one.

What a Difference a Year Makes

The relative coolness (and pleasantness) of this past summer was even more pronounced since it followed the hot and humid Summer of 2002 and inevitably, comparisons are bound to be made. The Summer of 2002 was one of the hottest in history across Southeast Lower Michigan, ranking the 11th hottest in Detroit (out of 133 summers since 1870, it placed in the top 8% hottest summers)! At Flint, it was the 7th hottest summer on record (out of 61 summers since 1942, placing in the top 11% hottest summers). An abundance of 90 degree or higher days were chalked up in last summer, while this year there were few (see below). Not only was the Summer of 2002 hot, it was overall drier than this past summer. The period of mid June into mid July last summer was hot and exceptionally dry.

The Summer of 2003 will go down as a comfortable summer with near normal to below normal temperatures and really, just a hand full of miserably hot and humid days. Basically, the area south of a Lansing - Flint - Port Huron line (or south of I-69 to the Ohio border), saw temperatures average right around normal. Further north in Southeast Lower Michigan (or north of I-69), temperatures overall, averaged around a degree below normal.

June was by far, the coolest summer month with all of Southeast Lower Michigan averaging below normal. In fact, with an average temperature of 64.6 degrees, Flint had its 12th coolest June on record since 1942 (Fig-1). Some warmer (or even hot) days began to make more of an appearance during July but still there were some relatively cool days. While temperatures averaged closer to normal over much of the area during July, generally below normal readings still could be found over portions of the Saginaw Valley and Thumb Region. August, by far, turned out to be the warmest month across the entire region as evidenced by both Detroit and Flint averaging around a degree or two above normal. Ironically, Flint recorded its 13th warmest August (Fig -1) on record while Saginaw's average temperature crept slightly above normal. Here at the NWS White Lake (and over 1000 feet elevation) we had the coolest average summer temperature of the four stations with just 67.1 degrees. We have yet to establish normals here at DTX, but that 67.1 degree average temperature leaves little doubt that it would have placed below normal.

The daily high temperature at Detroit hit 90 degrees or better on just four days this summer as compared to 25 hot and sticky 90 degree or better days last year. Granted, it is still possible we may register 90 or better sometime in September (or even in early October, by record high temperature standards), but at least through the summer months of June-August, four is the total. Flint also recorded four days this summer with temperatures at 90 degrees or better, while Saginaw came in with five. Last summer Flint had 24 days that reached 90 or better, while Saginaw totaled up 13. In any event (and maybe not surprising), all areas had considerably below the normal days of 90 degrees or better for the warm season. Detroit typically can expect about 12 days during the warm season that temperature hits 90 or better, while Flint and Saginaw average about seven.

Rainfall amounts for the summer varied considerably across Southeast Lower Michigan. One can see a fine example of that when comparing all rainfall reports in Figs 1 and 2, where rainfall totals ranged from less than six inches /5.74/ - and the 16th driest summer on record - at Saginaw to more than double that with over twelve inches /12.16/ in the city of Monroe. While rainfalls varied considerably from one place to the next, a few subtle trends were identified. Heavier rains tended to be over portions of the Saginaw Valley and Thumb Region in July, and over the extreme southeast corner of Lower Michigan near the Ohio border in July and/or August. Then, ironically much of that same region (Saginaw Valley and Thumb Region) saw significantly drier weather develop later this summer. In these areas, it truly was "feast or famine" in regards to rainfall (sometimes in the same county)! Another good example of the summer "feast or famine" rainfall regime, while Saginaw had its 8th driest August on record with just one inch of rain, Flint had its 17th wettest August with 3.79 inches!

Drought Monitor, September 9, 2003; Click on image for full map The return to dry weather across this region as of late, has just exacerbated the dry/drought conditions already plaguing this area for sometime. As of early September, the Saginaw Valley and Thumb Region has been placed in a moderate drought (current data). However, if one had to determine the region with the least rainfall this past summer, it appears to have been the middle part of Southeast Lower Michigan. This area extends roughly from portions of Livingston - Oakland - Macomb and St Clair counties northward into Shiawassee - Genesee - Lapeer and Sanilac. As a result, in early September this area too had been deemed abnormally dry or in a moderate drought.

Regarding this summer rainfall pattern, in the Summer Outlook Update issued mid July the following was stated:

It should be noted, however, we have yet to see our " normally" (87% of the time) occurring summer dry spell, when in a two to four week span, less than a half inch of rain falls. In another in-house study, it was found that the best chance for a dry spell historically is approaching and is from mid August into early September with mid July to early August a close second (for more information, check our earlier study titled "Summertime dry spells in Southeast Lower Michigan are more common than you might think".

Those areas drying out (see Figs-1&2) since mid or late summer just mentioned above, now seem to be in the process of having that dry spell by the looks of the rainfall totals in August into early September (and also is reflected in the drought index update).While there were locally above normal rainfall amounts this past summer, the majority of the region received normal to below normal rainfall. When taking the summer rainfall normals of Detroit, Flint and Saginaw, the normal (or average) for all of Southeast Lower would be 9.47 (coincidently, that amount was Detroit's exact 2003 summer rainfall /9.47/ and it just .03 shy of Detroit's 100 year average summer rainfall /9.50/).

SUMMER 2003 (Fig-1)

(See Legend under Fig-2)
Detroit66.6 / 2.5172.6 / 2.5972.9 / 4.3770.7 / 9.47
Departures-2.4 / -1.04-.9 / -.57+1.1 / +1.27-.7 /-0.34
Flint(12) 64.6 /2.15 -16-  70.8 / 1.70 -12-  -13- 70.9 / 3.79 (17)  68.8 / 7.64 -16- 
Departures-1.6 / -.92.2 / -1.47+2.4 / +.36+.4 / -2.03
Saginaw64.5 / 2.10(18) 69.4 / 2.6469.5 / 1.00 -8-67.8 / 5.74 -16-
Departures-2.3 / -.96-1.8 / +.14+.8 /-2.38-1.1 / -3.20
NWS White Lake63.1 / 3.2468.8 / 2.7269.5 / 3.0867.1 / 9.04
(Departures based on standard 30yr norms)

Some Selected Monthly/Summer Rainfall Amounts from NWS Cooperative Observers (Fig-2)

Bad AxeHuron2.983.31.927.21
Port HuronSt Clair2.712.671.657.03
Mt ClemensMacomb3.211.161.796.16
Ann Arbor /UOM/Washtenaw2.272.931.146.34
Grosse Pte FarmsWayne3.240.723.257.21

mid to late summer dry spell

Reflecting on the Summer Outlook issued at the open of the summer regarding temperatures:

Referring back to the 13 summers researched (Fig-3) and temperature forecast issued in the Summer Outlook at the open of the summer season.


Summer ofTemp/PcpnJuneJulyAugust
1882- 69.4 / 9.78 +/-  66.6 / 3.70  70.3 / 1.65  71.4 / 4.43 
1886- 70.1 / 8.67 - 67.9 / 2.4571.6 / 2.0270.8 / 4.20
1914- 70.7 / 8.89 - 68.0 / 3.2572.7 / 1.8071.4 / 3.84
1924- 68.7 / 5.64 -12- 65.6 / 3.1569.9 / 0.7870.7 /1.71
1932+ 72.3 / 8.48 - 70.3 / 1.3573.0 / 3.1173.7 / 4.02
1940+/- 71.4 /11.95 + 67.6 / 3.2773.4 / 1.1773.1 / 7.51
1954+/- 71.1 / 7.05 - 71.3 / 2.9771.8 / 2.0170.3 / 2.07
1964+/- 71.6 /10.59 + 69.6 / 2.3576.0 / 2.3769.1 / 5.87
1973+/- 71.8 /11.19 + 69.9 / 4.8672.6 / 4.6672.9 / 1.67
1978- 69.8 / 6.39 -20- 66.8 / 2.6970.6 / 1.9771.9 / 1.73
1988 -3-+ 74.2 / 6.53 - 70.4 / 0.9777.1 / 2.4375.1 / 3.13
1992 (2)- 67.0 /10.76 + 65.5 / 2.3568.8 / 5.9166.7 / 2.50
1995 -1-+ 74.5 / 8.66 - 71.6 / 1.5574.7 / 3.4077.1 / 3.71
Mean:71.0 / 8.81 - 68.5 / 2.68 -  - 72.5 / 2.56 -  + 71.9 / 3.57 + (Means of study summers)
200370.7 / 9.47 - 66.6 / 2.51 -  - 72.6 / 2.59 -  + 72.9 / 4.37 + (Means for Summer 2003)
100 Year Average-71.0 / 9.50
30 Year Normals-71.4 / 9.8169.0 / 3.5573.5 / 3.1671.8 / 3.10
( ) Coldest or Wettest Ranking 
- - Warmest or Driest  Ranking                                                 
 +  above normal
 -  below normal
+/- normal (within .5 degree or .50 precipitation)
    (30 year norm)

Based on Detroit's data from selected summers and recent trends, the following was noted and predicted for the Summer of 2003 in the outlook.

"One of the first things that strikes the observer when looking at the above summer data (Fig-3) is the dominance of cool to near normal summers. Out of the 13 summers in the study, six averaged below normal and four averaged near normal, therefore, ten of the 13 summers averaged near normal to below. Only three of the 13 had temperatures that produced a warmer than normal summer.

The local data suggests the summer's average temperature is expected to fall within the normal range. The best chances of normal to above normal temperatures will come mid to late summer. Generally, the coolest weather (or best chances for below normal temperature departures) was in June or in some cases, even into early July, where the dominant cool upper flow persisted the longest. The warmest weather (or best chances for above normal temperature departures) was generally seen in July and/or August. Still, this summer is not expected to be as warm as last summer nor contain as many ninety degree days."

The temperature pattern found in many of the previous summers in the study was also very evident this past summer in Southeast Lower Michigan. When one looks at Fig- 3 (above) and compares Detroit's summer averages in the study to this past summer, note the similar trend. Our coolest or below normal temperatures did indeed come early to mid summer, while the warmest (near normal or above) came in August. August was the only month that averaged around normal in the study. Both June and July not only averaged below normal in the study but also during this past summer. Overall, the same "cooler to warmer trend" found in the monthly averages in the study, was well represented during this past summer (it was just a bit more exaggerated). While this past June turned out to be cooler than the June average in the study, this past July's average temperature was almost a dead ringer for the July average in the study. Typically, Southeast Lower Michigan experiences its warmest weather of the summer during July. August's average temperature turned out to be warmer than the August average in the study.

Another interesting similarity in the summer study versus Summer of 2003 is when one compares Detroit's 2003 summer average temperature to the projected average in the study. This past summer's average temperature of 70.7 was just a few tenths of a degree lower than the 71.0 projected by the13 summer average temperature.

Reflecting on the Summer Outlook issued at the open of the summer regarding precipitation and severe weather:

The convective rainfall pattern this summer still reflected the busy winter and spring storm track into the Ohio Valley and Southern Great Lakes. Though seasonally weakening this summer, the storm track continued impressively active. Several systems brought rounds of heavy convective rains into the Northern Ohio Valley and occasionally further north, into Southeast Michigan. Based on the spring and summer research earlier this year, it was anticipated that the Severe Weather Season of 2003 would be active due to the expected only gradually weakening of the northern jet stream and an active storm track in the Great Lakes and Northern Ohio Valley:

Severe Weather Season:

"The severe weather seasons proved to be rather early/active in the majority of the springs checked, and especially in the 1970s (the two in the study, 1973 and 1978 and others). Like the past winter, this spring also followed the trend of the two "70s" winters with a rather active/early severe weather season. One explanation for this past spring (and in some of the researched springs) was the persistence and relative strength of the southern jet stream and subsequent storm track into Southern and Central Great Lakes.

The dominant storm track still favors the Northern Ohio Valley (wet conditions have dominated across the Ohio Valley). As a summer pattern establishes itself, it is likely this pattern will retreat further north into the Great Lakes (similar to that of 1973). This would support rainfall across the region to continue to more generous (but more scattered) into the summer months...unlike the past few summers. This, along with more intermittent and weaker northwest upper flow (that would still supply the occasional clashing of air masses) and this would point to a normal, if not locally above normal, rainfall scenario"

While the summer pattern did remain active, the heaviest rains remained over the extreme southeast corner of Lower Michigan (as evidenced by the 12.16 inches at Monroe). Only temporarily (July) did the heavier rains materialize further north in Southeast Lower Michigan. The projected rainfall amounts for both June and July at Detroit and the actual amounts for those two months this summer complimented one another nicely. Although this August's rainfall was somewhat more than the average found for Detroit in the study, it still was in keeping with idea that August would likely be the wettest month in Detroit. Storms with the heaviest rains continued to batter the Northern Ohio Valley throughout the summer, occasionally producing flooding conditions rather than lifting and staying north in Lakes. The rainfall pattern of August across our region reflects this activity best with heaviest rains remaining over the extreme south where Monroe reported over six inches /6.22/ of rain..

Summers of 1973 and 1978 versus 2003

During the past several seasons, similarities to both 1973 and 1978 (temperatures and rainfall patterns) have been mentioned in past outlooks and subsequent reviews - and this past summer was no exception. This time, however, the summer patterns of each year were more opposite of each other with the Summer of 1973 being warmer and wet (stormy), while the Summer of 1978 was cooler and drier. Curiously, this past summer's pattern actually did reflect trends of both summers with the normal to below normal temperatures of 1978 and the stormier pattern of 1973. In addition, even with the active storm pattern this summer, the drier weather pattern of 1978 was still quite evident, especially late this summer in the areas mentioned above (though Detroit itself had a wetter August). Like the 70's summers, this past summer also displayed its warmest weather late in the season (August) along with that drier weather.


Ironically, when comparing the 100 year normal temperature /71.0/ (the best representation of a normal summer average temperature for Detroit), the Summer of 2003 pretty much fit the bill at 70.7! Even in regards to the100 year normal rainfall, we were almost an idea match with 9.47 of the 9.50 falling.

An overall near normal summer was expected for Detroit, while ten out of 13 previous summers in our research suggested a normal to below temperature biased for all of Southeast Lower Michigan. While convective rainfall is harder to predict due to the simple nature of the rains (feast or famine genre), overall rainfall across Southeast Lower Michigan was normal to below normal (with pockets of above normal rain). In the study, eight out of the 13 summers contained normal to below normal rainfall. Rainfall overall, however, was still more generous than the Summer of 2002. When conversing with several inhabitants of Southeast Lower Michigan (including several gardeners and a few farmers), the Summer of 2003 will be remembered containing pleasant temperatures and sufficient rainfall which lead to a good growing season until late summer, when a good portion of the region dried out.

Autumn Trends and Outlook:

While more definitive trends were discovered while researching for the past several seasons, the trend for the upcoming fall season is more variable and less discernable. Despite this lack of "visibility", a few subtle but noteworthy items surfaced.

Overall, temperatures early to mid autumn tended to average normal to above with rainfall normal to below. As the season progressed, temperatures and rainfall trends were more variable.


While September's pattern tended to be mixed as far as temperatures (warmer, cooler), rainfall generally was below normal (eight out of 13 were drier than normal). September of 1973 and 78 were both warmer and drier than normal, and ironically, both recorded 1.82 inches of rainfall. Only three Septembers in the study were wet, 1886 with 4.20 inches, 1932 with 4.05 and 1992 with 5.55.

A somewhat stronger temperature trend was seen in October with eight out of 13 Octobers averaging above normal. This offers some encouraging signs for Indian Summer weather this fall, unlike last fall when we went from summer-like to winter-like weather in mid October. Rainfall varied considerably from just .47 in 1924 to a whopping 7.80 inches in 1954.

November's weather was more mixed again with equal chances of above or below normal temperatures and rainfall (and snowfall).

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

Autumn arrives: September 23rd at 647 am 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.