Cool Summer To Persist?

WILL THE SECOND HALF OF THE SUMMER BE ANY WARMER THAN THE FIRST?

By; Bill Deedler, Weather Historian - National Weather Service, White Lake Mi

A quick answer to the headline question might be…Well, it wouldn’t take much!  The persistence of cooler than normal weather this July (and summer as a whole), has been exceptional!  Meaning, not that it’s been great (but there are some who would argue that point), but the summer sure has been unusually comfortable in regards to heat and humidity.  If the July average was calculated for the first half of the month /thru 15th/ at the three climate locations, the average temperature would place at/or second for coldest July on record.   See below:  top 5 coldest/warmest Julys on record and where we stand this July at Detroit, Flint and Saginaw. 

Top 5 Coldest/Warmest Julys
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
67.1
1891
79.0
1955
64.0
2009
78.0
1921
64.5
2009
77.5
1921
2
67.9
2009
79.0
1921
66.9
1992
77.7
1935
66.2
1992
76.8
1916
3
68.8
1992
77.9
1916
67.3
1967
76.7
1934
67.1
1924
76.2
1935
4
68.9
1967
77.7
1931
67.3
1962
76.5
1955
67.2
1920
76.0
1931
5
69.6
1971
77.1
1988
67.4
1971
76.1
1931
67.3
1945
75.9
1955
 

It’s interesting to note that the coldest July on record at Detroit was in the first summer /1891/ of our analogue years (table further down and let’s hope history doesn’t repeat itself). Not only has the magnitude of the cool weather been notable this summer, but so has its persistence.  

Looking back on the first half of the summer /six weeks/, temperatures across the region have averaged a fairly large below normal departure (for the summer months). On the rainfall and storm front, in spite of the heavy rains and scattered storms in June and early July, some areas are beginning to dry out. The Saginaw Valley area has seen less rain than the Flint region. It must be mentioned however, much of this rain at Flint was due to exceptionally heavy rain on June 17th when 3.46” deluged the area.

 

Summer 2009 Statistics for the first half /six weeks/.

CITY
 
Temp
Depart
Rainfall
Depart
DETROIT
67.8
-2.5
5.28
0.14
FLINT
64.9
-2.6
6.57
1.93
SAGINAW
65.3
-2.8
3.60
-0.68

 

Checking out our coolest summers on record (see: top 10 coldest/warmest Summers on record below, note where we stand as of mid July, temperature- wise at Detroit, Flint and Saginaw). 

 
Top 10 Coldest/Warmest Summers
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
64.9
2009
72.3
1949
64.8
1915
73.0
1933
2
67.0
1992
74.5
1995
65.4
1992
72.2
1955
65.1
1992
73.0
1931
3
67.3
1927
74.5
1955
66.2
1958
71.8
1988
65.3
2009
72.5
1955
4
67.5
1875
74.2
1988
66.3
1960
71.7
1995
65.5
1982
72.3
1995
5
67.6
1903
74.0
1933
66.5
1969
71.7
2002
65.8
1945
72.1
1930
6
67.8
2009
73.8
1949
66.6
2004
71.7
1987
65.9
1950
72.1
1921
7
67.8
1985
73.7
1921
66.7
1985
71.6
2005
65.9
1924
72.0
1988
8
67.9
1912
73.6
1952
66.8
1972
71.6
1983
66.1
1985
72.0
1937
9
67.9
1907
73.5
1991
66.8
1967
71.3
1944
66.4
2004
71.9
1936
10
68.1
1982
73.5
1959
66.9
1962
70.8
1952
66.4
1979
71.7
1998

 

So how does this relate to our past analogue summers used in the local Summer Outlook for Southeast Lower Michigan? The first half of the summer has aggressively played out as discussed in our outlook (see below). 

 "With the Southeast Michigan being so close to the Eastern Canadian trough (with ridging support over northwest Canada), it is thought a more pronounced Eastern Canadian upper low will continue to be a main influence in our weather. Actually, the main features (red arrows) I feel that are worth watching this summer are nicely displayed in the present upper air pattern /as of 6/2/09‐200 MB/ these first few days of June (map below).  It is believed that these three players should make for an interesting summer. The aforementioned strong blocking pattern remainingover Canada late this spring routinely delivered some impressive cold shots south into the northern third of the country”

 “Our selected analogue years do tend to imply a building ridge axis over the center part of the country, shifting from west to east and flattening with some of the more potent cold shots from Canada. Therefore, something’s got to give. While some seasonal weakening of the Canadian trough can be expected, it still should be a competent competitor much of the summer.”

Below was the map example used:

This pattern, in varying degrees, has been the case much of the first half of the summer. The Canadian blocking pattern has dominated, to a large extent, and has resulted in a parade of strong and fairly cold upper low pressure systems dropping southeast into southeast Canada.  Periodically, when the ridge (also mentioned above) has built into the lakes, it has routinely been flatten by the Canadian trough. This has been the main reason why our summer thus far has been so cool. As of mid July, all stations are averaging 2 ½ to nearly 3 degrees below normal.  While it was forecast that our coolest part of summer would come the first half (from the Outlook), what can be expected the remainder of the summer?

“there are still a few trends to watch for this summer; one being the warmest weather (relative to normal) will come mid to late summer (July and/or August). The stubbornness of the trough in Canada along with some of the cold June’s found gives a little more credence to the warmer temperatures mid‐late season.

Note in the Detroit table below, the June months at all three stations were fairly mixed, However, in not one July did the temperatures average warm enough (>+1.0 degrees) to be placed in the above normal category (all were normal or below). In fact, the average temperature departure overall the analogue July temperatures came in 1.4 degrees below normal. As one can also see in the table below, five summers averaged below normal (better than a degree), eight averaged within a degree of normal and only two averaged above. Moving into August shows more mixed results (like June) but there were still a good number of normal to below. 

 

 

Remainder of the Summer:

Temperatures

Keeping one eye on our upper air pattern and the other on our analogue Augusts, even if we do warm some, the overall summer should average lower than the normal category (-1.0 to 1.0) used for the analogues.  Simply put, it was expected the warmer second half of the summer would offset some or most of the below normal departure established the first half.  While the forecast of below normal has materialized the first half of the summer, due to the magnitude of the cool weather, the aforementioned tenacity of the upper low (and associated pattern) in Canada and the mixed data of the analogue Augusts, I’m looking for below normal departures to prevail in the neighborhood of one to three degrees for the entire summer in the end.

I feel it’s reasonable to still stick with a warmer second half of the summer over the first as discussed (and, asked at the beginning of the article) so don’t give up and put away the bathing suits just yet. 

Rainfall

On the rainfall front, normal to locally above normal rainfall was forecast and that has played out thus far. It was discussed early-midsummer was expected to be the wettest with dry spells more prevalent mid-late summer. Under wet summer scenarios discussed (especially early-mid summers), the following was written and tagged in the Outlook for this summer.

The upper air pattern seen late spring could easily evolve into one of these patterns as the summer heats up and the trough in Canada holds somewhat tough, somewhere a confluent zone will likely set up. At the same time, a dry or drier spell this summer looks just as likely and there‐in‐lies the problem (between dominant dry summers and less dominant wet). Therefore, and going with the trend seen, rainfall looks to be heaviest early to mid summer with drier weather later.

 We’ll check and compare the first half of the summer versus second half in the Summer Review/Autumn Outlook due early September.

 

 

 

 



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