"Dog Days of summer is the name for the most sultry period of summer, from about July 3 to Aug. 11. Named in early times by observers in countries bordering the Mediterranean, the period was reckoned as extending from 20 days before to 20 days after the conjunction of Sirius (the dog star) and the sun."
The expected upper wind pattern across the country discussed in the Summer Outlook has verified extremely well for the first half of the summer with the two moderately strong jets (Polar and Pacific) occasionally phasing and vying for dominance.
A good example of the prevailing jets expected this summer (see further below); also shows on the map below, taken from a recent model prog panel. Note the persistent oscillating North American pattern thus far this summer (as described in the Summer Outlook). The Pacific jet continues sending shortwaves into the mid part of the country, which flatten the summer ridge only to occasionally phase with the Polar short waves digging south into the eastern half of the country. There has been no shortage of storms and severe weather this warm season where one, or both of these jets pass over the country. Though occasionally getting clipped with severe weather in Southeast Lower Michigan (most notable June 22-23rd), we have missed the bulk of the severe weather to a large extent as heat and humidity bubbles up across the Midwest and Ohio Valley; only to be shunted east many times just south of the Lakes Region. This has been courtesy of our friendly Polar Jet which also has made summer temperatures quite tolerable (see maps below). Looking ahead to the second half of the summer in this regard, I would expect the upper ridge to give more equal showing than the first half, providing Southeast Lower Michigan more summer-like temperatures and resulting storms. At the same time, the Polar jet shows she's here to stay; routinely visiting through the rest of summer.
From the Summer Outlook:
Glancing at the upper wind projection for the Summer of 2013 show similarities to this summer and differences. The difference noted for this summer 2015 projection is the better subtropical jet projected and thus, a more variable upper ridge strength. This is a result of building and flattening ridging in response to short waves riding in and through the region from the west. This is depicted on both maps with the first a computer generated 500 Heights and my interpretation of active areas of surface patterns. The second map, my interpretation of summer dominant and placement of air masses.
Broadening this summer discussion out a bit, the first half of summer (or the first six weeks); temperatures across Southeast Lower Michigan have averaged a "comfortable" 69 at Detroit; 68 1/2 at Flint and 68 at Saginaw. A quick average and rounding gives us an average for the first half of the summer of ~ 68 1/2. Delightful temperatures none-the-less if you like a comfortable summer; which is just so happens what the analogues called for in the Summer Outlook.
Analogues favor the cooler side of normal which seems reasonable considering upper wind patterns over Canada and El Nino trends. The analogue summers were extremely variable but with definite trends within with four cooler than normal, six normal and two warmer with a generally a comfortable summer projected. Not surprising, the average temperature while in the normal range, leaned a bit toward below normal - makes perfect sense with twice as many cooler than warmer summers. This is not surprising as El Nino Summers lean toward the cooler side of average. Also, the chances of long hot spells are less than average and subsequently; average to below average /8-12/ so too are the amount of 90 degree days.
In defense of the summer weather thus far, looking at the actual statistics and norms it may also surprise you that even though the summer's been on the cool side, the summer hasn't been all that terribly cool, statistic-wise. While temperatures have averaged around 68 1/2 across the ENTIRE region, it's the departure from normal at Detroit which makes it seem much cooler. Detroit's normal are skewed UP about 1 1/2- 2 degrees higher than the normals at either Flint or Saginaw due to the heat island. June norms are as follows: 69.4/ 66.5/ 67.2 respectively and July normals include the following; 73.6/ 70.5/ 71.0 for Detroit, Flint and Saginaw. Those stats alone show the preference for a metro Detroit warmer heat island. Realistically speaking if no heat island existed at Detroit, the normal at Detroit IMHO should be only about a degree or so warmer than Flint and Saginaw. Therefore; the average temperature across Southeast Lower Michigan for the first six weeks is running roughly a degree below normal when all three locations are averaged together and separately; Detroit ~ -2.2, Flint and Saginaw area ~0.4 degrees
If we briefly scan the 20 coolest summers list at all three locations and even if we continued to average right where we are now for the rest of the summer; only Detroit just nicks the top 20 list of all three locations. If we average just near normal the rest of the summer, temperature averages would rise some.
Again Detroit's at about 69, Flint's 68 1/2 and Saginaw 68 thus far
Top 20 Coldest/Warmest Summers in Southeast Lower Michigan
|Rank||Detroit Area*||Flint Bishop**||Saginaw Area***|
|* Detroit Area temperature records date back to November 1874.|
** Flint Bishop temperature records date back to January 1921.
*** Saginaw Area temperature records date back to January 1912.
Average Temperature Departure maps
While heat has been lacking this summer thus far, rainfall has NOT; especially across the southern counties of Southeast Lower Michigan!
Location Amount Norm Dep
Detroit: SINCE JUN 1 6.25 4.95 1.30
FLINT: SINCE JUN 1 7.64 4.44 3.20
SAGINAW SINCE JUN 1 5.74 4.11 1.63
To maintain the integrity of my Summer Outlook; the second half of the summer should be drier across the Saginaw Valley and Thumb region while normal to above rainfall continues across the southern two thirds, since all areas are now above.
I look for rainfall to be quite variable as mixed data presents conflicting results and where and how much may also be exasperated more than what is typical for many summers. Taking all data (past and present) into account; rainfall is expected to be above normal over the southern sections of Southeast Lower Michigan and normal to possible even below across the Saginaw Valley and Thumb Region. As with temperatures, timing of the wettest and driest periods will be quite variable - not unlike the spring.
Also; This is similar to 2013 where heavy amounts were seen over the south and lighter, below normal amounts were observed in the Saginaw Valley and Thumb.
Rainfall Totals Departure maps:
The wet June stands out like a sore thumb, a subtly drier pattern has begun to emerge in July - and mainly in the Thumb/Saginaw Valley region - BUT it is too early to call it a trend and we'll stick by the original forecast. I'll give my original summer forecast time to hopefully work out for all areas.
And with that, this brings me to my Outlook for the Remainder of the Summer
And, to that - little overall change to my original call with Temperatures averaging 1 1/2 below to 1 1/2 above normal while rainfall is above across the southern sections (Flint area to Port Huron south the Ohio border) and normal to below across the Saginaw Valley and Thumb Region. Most areas should see adequate rains this summer if past and future is any guide.
Temperatures overall (and this should balance out the first half some), I look for warmer temperatures on average with more normal to above normal the second half of the summer as upper ridging gains some ground - so don't count the summer out just yet!
Bill Deedler -SEMI_WeatherHistorian