Strong Dominant Hot Ridge and Occasional Deep Upper Low in Eastern Canada Responsible for Very Warm and Dry Pattern Thus far This Summer /Updated 90 stretch - DTX/

The Summer of 2012 has started just like the past few summers with plenty of heat with above normal warmth across Southeast Lower Michigan. Now with the last day of June recorded in the record books; June of 2012 will go down as the 9th warmest June on record placing a smidgen ahead of 1994's 72.2 (originally 9th place) with an average of 72.3. This places it right smack dab between 1994 and 1991.

Interestingly; neither Flint nor Saginaw placed in the top ten warmest Junes. In fact, Flint did not even place in the top 20 warmest Junes; while Saginaw placed down at 17th. Flint's June average temperature was 69.2 degrees, while Saginaw's average was 69.8 replacing 1987.

Top 20 Coldest/Warmest Junes 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	62.8	1985	74.6	1933	60.1	1969	75.0	1933	60.6	1982	73.9	1933
2	62.8	1903	74.1	2005	60.9	1958	74.9	1934	61.0	1926	73.5	1919
3	63.1	1915	74.0	1919	61.5	1980	72.1	1949	61.5	1915	72.3	1971
4	63.4	1928	73.3	1949	62.5	1985	71.7	1925	61.8	1958	72.3	1934
5	63.4	1926	73.2	1934	62.5	1972	71.5	1921	61.9	1917	71.7	2005
6	63.4	1916	72.8	1943	62.9	1982	71.3	1943	62.1	1980	70.6	1931
7	63.6	1927	72.7	1952	63.1	1977	71.2	2005	62.1	1916	70.5	1976
8	63.7	1980	72.4	1991	63.3	1960	70.3	1952	62.3	1945	70.4	1949
9	63.7	1889	72.2	1994	63.4	1928	70.3	1987	62.7	1977	70.3	1967
10	63.8	1878	71.6	1995	63.6	1945	70.3	1939	62.8	1985	70.2	1932
11	63.9	1958	71.6	1890	63.8	1927	69.8	1931	62.8	1928	70.0	1995
12	63.9	1902	71.5	1944	64.2	1992	69.8	1923	63.2	1947	69.9	2007
13	64.1	1917	71.4	1921	64.5	1947	69.7	1991	63.2	1902	69.9	1923
14	64.2	1982	71.3	2007	64.6	2003	69.6	1954	63.3	1903	69.9	1930
15	64.2	1972	71.3	1954	64.7	1961	69.6	1932	63.5	1969	69.9	1921
16	64.4	1881	71.3	1987	64.9	1986	69.5	1971	63.7	1972	69.9	1911
17	64.6	1935	71.3	1923	64.9	2009	69.5	1944	63.8	1927	69.8	1987
18	64.6	1897	71.2	1895	64.9	1974	69.4	1941	64.2	1978	69.7	1999
19	64.7	1969	70.9	1953	65.1	1978	69.4	1930	64.2	1940	69.7	1901
20	64.8	1907	70.8	2002	65.1	1948	69.3	1976	64.2	1924	69.6	1943
* Detroit Area temperature records date back to January 1874. ** Flint Bishop temperature records date back to January 1921. *** Saginaw Area temperature records date back to January 1900.

 
Why the discrepancy between Detroit, Flint and Saginaw? Again, mainly because of the heat island effect at Detroit Metro Airport. And, not just the overnight lows on the hottest of days but also on the coolest of nights! The reason both Flint and Saginaw placed so much lower in the top 20 hottest Junes (or not at all) was the decidedly, refreshing cool blasts that occasionally occurred during the month. This was due to our friendly cool upper low pressure centered over eastern Canada that plopped its caboose far enough south over the Great Lakes and Northeast, to break the hot spells. Of course, these cooler infiltrations happened at Detroit too but on several occasions; that cooler air was introduced across the region on a north to northeast wind. This is not conducive to the coolest of nights at Metro with the wind flow across the urban and suburban areas into Metro Airport.

With all the heat lately, it is easy to forget the strong cool blasts Southeast Lower Michigan did see in June. As a comparison; Flint's temperatures fell into the 40s for overnight lows ten times during the month and two of those were 42 degrees, ten degrees from freezing! Saginaw saw overnight lows fall into the 40s five times with the lowest; a double 46. Detroit had a lone 49 degree low for the month but still, there were numerous 50s. Take away the heat island effect; and I doubt Detroit would have placed much above the mid teens in the top 20 warmest Junes, like Saginaw. Unfortunately, this micro-climate does affect temperatures (mainly overnight lows) at Detroit and several other major cities...polluting long term records (but don't get me started ;-)).

Last year's hot Summer of 2011; tied with 2010 in Detroit at 74.4 for fourth hottest summer! We also did end up with 23 days where the temperature rose to 90 degrees or better. Thus far we are moving right along on the 90 degree track again with already 11 days of 90 degrees or better at Detroit; average is about 12-14. Even though Flint did not place in the top 20 warmest Junes; there still were 7 days with 90 degrees or better in June and one 100 (8 for the season). This is the best example of the contrasting temperatures during the month! Here Flint has had 7 days of 90 degree or better, including the 100...yet failed to even place in the top 20 warmest Junes! Want more proof? Get a load of Flint's June temperature extremes...100 degrees and two 42 degrees!

Why so hot; yet "so cool" with average temperatures just  2 1/2 degrees above normal? DRY! That's right, the upper wind pattern thus far this summer has been conducive to bring the blistering heat out of the Great Plains and Midwest, east into the Great Lakes. While to a lesser extent, the upper flow over Canada has occasional been impressive enough to break through the hot ridge and back it off further west and  thus keeping the worst of the heat; west and southwest of us until really just this past several days. While this has helped in the temperature department somewhat; it had added to the dry conditions. When these cooler air masses have surged out of Canada, they flow across the relatively, cool and dry continental regions of Canada. This, combined with the prevalence of the strong hot ridge west and over us; has lead to a relatively scant moisture supply being the usual Gulf summer moisture has been cut back some. 

Since the hot ridge has been so dominant over the country; increasingly dry soil conditions are exacerbating the heat and thus, exacerbate the dry conditions. Simply put; they feed on one another!  That's why it's been so easy to pop into the 90s...just look at your yard...it's becoming semi-arid out there in many places! This comes, of course,  at the worse time possible in the growing season. Many areas are at least two to nearly four inches below normal in this years growing season! A season that still has at least two solid months left yet. I feel this dry weather phenomena is just as important as any heat (and there at least so far, we've had some relief).

Check out the latest Drought and Dry Index Map>>>

 This map below, shows the growing season (90 day) precipitation (or really lack of), percent of normal departure.

And this map below, shows the expansion for the below normal rainfall for June (30 day percent of normal).
Note the worsening dry conditions as relayed by the percent of normal rainfall (or really, lack of).

Next up...
With the dominance of the hot ridge of high pressure thus far, I will be updating my Summer Outlook for the region by boosting temperature departures a bit higher anyways than I originally indicated. On the precipitation side of things; drier conditions looked like they'd be most likely from I-69 south; across two-thirds of the region. Preliminary indications here are; I will likely encompass the whole region but want to look at some indicators.

So then; will strong hot upper ridge continue to be the dominant player in our weather or will it begin to be squashed more often by the Canadian Low? And what of severe weather? Thus far, most of the action has been around us, especially south...will this continue?

Look for my mid-summer update within a week or two!

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