Certainly one of the more comfortable summers than in recent years was enjoyed across Southeast Lower Michigan in 2013. Projected temperatures in my Summer Outlook of around normal readings came to fruition along with why we would see a less hot and humid summer (see upper air pattern discussion). Careful, that above average temperature for the summer is misleading.
*Summer
2013
|
Average Temperature (Departure from Normal)
|
Normal
|
Immediate Detroit Area
|
71.9 / +1.1*
|
70.8*
|
Flint
|
70.5 / +1.1*
|
69.4*
|
Saginaw
|
69.7 / +0.7*
|
69.0*
|
* Data from NWS DTX - Summer Normals are computed based on each site's period of record, which is different than the 1981-2010 period used to compute individual monthly statistics
Comparing this summer's temperature averages to the past several shows one of the main reasons this summer felt cooler!
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
|
2005
|
65.4
|
1992
|
74.2
|
1933
|
64.8
|
1915
|
73.0
|
1933
|
2
|
67.0
|
1992
|
74.5
|
1995
|
66.1
|
2009
|
74.0
|
1934
|
65.1
|
1992
|
73.0
|
1931
|
3
|
67.3
|
1927
|
74.5
|
1955
|
66.2
|
1958
|
72.7
|
1936
|
65.5
|
1982
|
72.5
|
1955
|
4
|
67.5
|
1875
|
74.4
|
2010/11
|
66.3
|
1960
|
72.6
|
1939
|
65.8
|
1945
|
72.3
|
1995
|
5
|
67.6
|
1903
|
74.2
|
1988
|
66.5
|
1969
|
72.6
|
1931
|
65.9
|
1950
|
72.1
|
1930
|
6
|
67.8
|
1985
|
74.0
|
1933
|
66.6
|
2004
|
72.6
|
1921
|
65.9
|
1924
|
72.1
|
1921
|
7
|
67.9
|
1912
|
73.8
|
1949
|
66.7
|
1985
|
72.3
|
2010
|
66.1
|
1985
|
72.0
|
2010
|
8
|
67.9
|
1907
|
73.7
|
1921
|
66.8
|
1972
|
72.3
|
1949
|
66.4
|
2009
|
72.0
|
1988
|
9
|
68.1
|
1982
|
73.6
|
1952
|
66.8
|
1967
|
72.2
|
1955
|
66.4
|
2004
|
72.0
|
1937
|
10
|
68.2
|
1972
|
73.5
|
1991
|
66.9
|
1962
|
72.0
|
1935
|
66.4
|
1979
|
71.9
|
1936
|
11
|
68.3
|
1979
|
73.5
|
1959
|
66.9
|
1927
|
71.9
|
1938
|
66.5
|
1977
|
71.7
|
1998
|
12
|
68.3
|
1902
|
73.5
|
2002
|
67.0
|
1982
|
71.8
|
1988/11
|
66.6
|
1951
|
71.5
|
1934
|
36th warmest 71.9 2013 25th warmest 70.5 2013 36th warmest 69.7 2013
Perhaps no month displayed the temperature difference between this past summer and several previous summers than July. Note the marked contrast in temperatures and rankings this past July when compared to the past several Julys.
July 2013 Actual Normal Departure
Detroit 74.0 73.6 +0.4
Flint 73.0 70.5 +2.5
Saginaw 71.7 71.0 +0.7
Rank & Average
Temperature Records for July
Detroit
38TH
74.0 2013
|
Flint
22ND 73.0 2013
|
Saginaw
36TH 71.7 2013
|
Digging Deeper into the Summer Temperatures
Ok, so all these statistics show why this summer was considerably cooler and more comfortable when compared to the past several. While it's a given the average temperatures for the cities/summer were still a bit above normal, one must deep a bit deeper to really get the full picture. Where all temperature statistics really above normal over the region? And if not, what statistic wasn't above?
Looking across ALL of Southeast Lower Michigan paints a bit of a more complete picture. Note, average highs this summer actually averaged below normal. So it wasn't the highs that were above normal...and another reason it felt cooler this summer. During the day (where summer is typically measured by the public) on average, it was actually cooler than normal. It was the average low temperatures that came in above average for the summer. Enough above normal to push the summer averages just above normal statistical threshold when computed.
Even with the heat island influencing Detroit Metropolitan Airport temperatures, check out each monthly average high temperature compared to normal at Detroit. Every month failed to make its normal high. The average high for the summer comes out to be 80.6, nearly a full degree below normal. And, what does this say about areas away from the city?
Location June July August Summer
Detroit Ave High 78.5 82.5 80.9 80.6
Normal 79.3 83.4 81.4 81.4
Departure -.8 -.9 -.5 -.8
Another way people judge the summer is how many 90 degree days occurred? Normally Southeast Lower Michigan "feels" about 8-12 ninety degree days (depending on location). Here's another reason why it felt cooler than the statistics might want you to believe. Detroit had only five 90 degree days less than half its 100 year normal of 12. In addition, those 90s occurred all in one week in July when it was hot and humid. There were no 90 degree days in June nor August...highly unusual, especially August. Flint fared better with twice as many 90s /10/ than Detroit...which looks a bit strange at first glance but then add Saginaw's number of 90s to the mix /8/ and maybe not. (Just for the record, I do believe Flint's ASOS temperature runs about a degree or so hot when compared to surrounding sites). There is another reason Flint and to a lesser extent Saginaw chalked up more 90s than Detroit...moisture in the ground due to wide variances in rainfall between the cities. Simply put; Detroit had heavy amounts of rainfall this summer (see rainfall) whereas Flint just crept up to near normal while Saginaw was substantially below normal. Wet grounds tend to hold temperatures in the summer down a bit...not to mention the increased cloud cover due to more rain.
Number of 90s This Summer
City M J J A
Detroit 0 0 5 0
Flint 1 2 6 1
Saginaw 1 1 5 1
*Hot Spell - Detroit *Cool Spell - Detroit
July Hi Lo Av Dep Aug Hi Lo Av Dep
15 93 75 84 10 12 74 65 70 -3
16 90 77 84 10 13 69 55 62 -10
17 94 75 85 11 14 72 51 62 -10
18 94 75 85 11 15 75 51 63 -9
19 95 73 84 10 16 79 56 68 -4
*There were other hot & cool spells during the summer but these two were two of the most notable.
Summer Rainfall Tallies
Summer 2013 /Rainfall/ /Norm/ /Depart/ /Summer 2012/
Detroit 16.13 9.89 +6.24 3rd wettest summer
Flint 8.83 9.57 -0.73
Saginaw 6.53 8.94 -2.34 27th driest
The vast majority of the region saw suitable amounts of sunshine along with generous to abundant amounts
of rainfall during the summer. I say the vast majority since there were still some notable pockets of below
normal rain creating a minority of drier regions. All in all, good weather for gardens and vegetation was had
across the majority of the region with limited areas having rainfall deficiencies, those being mainly in portions
of the Saginaw Valley into parts of the Thumb (see second map; departure map). Ok then, how about too
much rain?
If anything; the occasional circumstance brought too much rain from thunderstorms with heavy to torrential rains which led to briefly saturated grounds. Heavy rains across extreme Southeast Lower Michigan brought predominately wet conditions to the far corner of the state. There was quite a difference in rainfall across Southeast Lower Michigan this summer! Totals (first map) ranged from only four to six inches over portions of the Thumb (mainly Bay and Tuscola Counties) to as much as 15 to 20 inches over parts of Monroe County. Note the departures above normal (second map below; based on radar rainfalls) of up to a foot, mainly over Monroe County. Heavy rains led to Detroit's third wettest summer on record. This summer was a classic example of where rainfall projections of below to above normal are most suitable (see Outlook performance)
SUMMER RAINFALL AMOUNTS - Radar Estimated
The last few heavy rainfall events were near the close of the summer with heavy rains on August 27-28th and again on the 30-31st. See maps below;
June Rainfall & Departure Map
June rainfall is one of the most important monthly rainfall for vegetation; note the wide variance this past June!
Upper Air Patterns of the Summer
The upper air pattern of the summer consisted of strong summer sub-tropical ridge that dominated over the Southern Plains and Desert Southwest which occasionally built east into the Upper Mississippi Valley and Great Lakes Region. This ridge oscillated as far east as the East Coast at times connecting with the summertime Bermuda High. Just as as important the ridge was the other main feature of the summer; a strong, below normal height upper low pressure system that dominated over northeast and eastern Canada. This upper low occasionally retrograded or redeveloped over south-central Canada. It was the interaction of these two patterns that created our comfortable summer.
In my Summer Outlook it was these two features I spoke about and why I thought this summer would turn out cooler than the past several. From the outlook;
Hemispheric Patterns
As the summer ridge builds into the center part of the country, I look for it to oscillate over the Great Lakes and the East, routinely bringing warm to hot weather to the region. However; it should be duly noted that the distinct upper air pattern that has been a key player since mid winter into spring, albeit naturally weakening with time and becoming less frequent, shows no signs of leaving during the summer. I'm speaking of the occasional blocking across the northern latitudes in which I expect to play a distinctive role this summer. By occasionally phasing with weaker mid continental impulses, troughing will dive into the Great Lakes and points east and thus, intermittently deliver enough cooler spells of weather to balance out somewhat the heat and humidity we do get, for a more normal and comfortable summer than the past several.
Based on the above upper wind pattern and analogue discussions below, my temperature forecast read as follows.
Temperatures
Recent hemispheric patterns and analogue summers (discussion below) suggest to me a more comfortable summer than the past several. In fact, temperatures should average closer to normal or average between 1.0 degrees below normal to 1.5 degree above.
Analogue Performance
Again from my outlook after researching other analogue summer;
Analogue Trends Seen
Temperatures
The Neutral analogue summers are really
quite mixed on the temperature front this time which is hardly
surprising given the hemispheric and SST environment. Even though
Detroit’s summer data
favors normal to below normal temperatures, one must closely compare
this data to
Flint and Saginaw. The reason being, the normals at Detroit were
increased in the
past few data sets (1971-2000 & also 1981-2010) due to mainly the
effect of
the local heat island that now encompasses the Detroit Metro Airport;
whereas Flint
and Saginaw saw little change in their normals. This would logically
then, skew
Detroit’s departure temperature data down somewhat. In any event; analogues suggest normal temperatures will prevail.
Rainfall and Severe Weather
Dominant trends past (previous analogues) and recent (past few months)
suggest variability in rainfall trends. April was wet while May was dry
relative to normal or average rainfall. While the majority of analogue
summers lean toward the dry side; a minority were especially wet!
We've already seen this wider range variability recently and it looks
like it will continue. When speaking of summer's total rainfall; I look
for a range of below normal to above normal given the present and past
trends
In Summary
The resultant Summer 2013 statistics reflect well my forecast for the summer including the projected upper air pattern and consensus of analogue data. Temperatures across Southeast Lower Michigan were kept in check which led to a more typical summer than recent summers due to the aforementioned upper air projections. Not to be outdone; projected rainfalls across Southeast Lower Michigan of below normal to above normal also materialized, mainly as a result of the forecasted macro-scale pattern, down-scaled for Southeast Lower Michigan.
Overall one could say it was a normal summer but with some hidden abnormalities (temperatures) and not so hidden (third wettest summer on record at Detroit and possibly worse points south).
Next Up; What's the Autumn Look Like??
Fall Color Time
Fall leaf color is basically caused by lack of sunlight and to a lesser extent is influenced by the late summer weather. However; drier than normal weather for the entire summer into early fall tends to accelerate the leaf changing process, causing the leaves to fall prematurely. Likewise, a wet late summer into September and October will tend to produce fewer vivid colors and the leaves may also fall earlier due to the rain, wind and storms.
The prime weather conditions which are conducive for brilliant fall colors are warm, sun dominant days and cool, crisp nights but without frosts or freezes; such as high temperatures in the 60s and 70s with lows in the upper 30s to lower 50s. These sharp, daily temperature swings and more importantly, the decrease in sunlight, play vital roles in the development of the leaf color. This combination of weather and lack of sunlight, creates a blocking effect on the sugars which are manufactured in the leaves and keeps them from reaching the root system. Eventually, these sugars convert to pigments that produce the vivid and brilliant colors seen on many trees in the fall. Evidently, the green chlorophyll in the leaves begins to fade during the shorter fall days with subsequently, less sunlight. Thus, the other color pigments already in the tree leaves are exposed, come out and produce the fall color splendor. The yellow color seen in some leaves is created by the xanthophyll pigment, while the orange-red color is caused by the carotene pigment and the red-purple color can be attributed to the anthocyanin pigment.
While color peak may vary season to season across Southeast Lower Michigan, generally the maximum leaf color occurs during the second and third week in October.
Making weather fun while we all learn,
Bill Deedler - SEMI_WeatherHistorian
