Summertime Temperatures
The Summer of 2017 will go down on average as a typical summer are far as temperature averages with all of Southeast Lower Michigan averaging close to a degree /+0.9/ above normal. In spite of the average temperatures being slightly above normal; the contradictory thing was the lack of 90 degree days during the summer months (which we have made up some in late September). Detroit recorded only 4 days with 90 or above, Flint registered 3 days of 90 or better and Saginaw just 2 - nearly all of the 90s were recorded in June which normally has the least of the summer months.
September's Outstanding Heatwave Changes Things:
As discussed last week in my blog; the upcoming heatwave had the potential to set some record highs and it did, and more....
Additional 90+ degree temperature highs were recorded recently in late September along with many being record highs. As of Sep 26th, Detroit has received 3 more days of 90 or better, Flint - 6 and Saginaw - 6. Therefore for this warm season; Detroit has now had 7 days of 90 of better, Flint has had 9 and Saginaw 8 days. Generally; 8-12 days of 90 or better are felt in SE Michigan during the year; the most generally being at Detroit.
Detroit attained three record highs with the final one of 93 on Sep 26th being the hottest of the records and hottest temperature ever recorded so late in the season. Note: on Oct 7th, 1963 Detroit reached 92 which had been the hottest so late in the season but given it's later in the season (though one degree cooler), to this climate guy - it still has just as much clout! Flint chalked-up an incredible six days of records, the last also being Sep 26th. Besides establishing six record highs, the 94 degrees reached on the 23rd set a record for the highest temperature ever recorded so late in the season. Up at Saginaw; they too had a six day string of record highs and the hottest day on the 24th of 94 also was the hottest so late in the season!
Summer Rains (Feast or Famine)
Rainfall for the entire Summer was quite variable from below normal to much above across the region and is best displayed on the rainfall maps (below). One notable exception to the rather inactive summer pattern occurred in late June over the far northern areas of Southeast Lower Michigan, Persistent, flooding rains fell on June 22nd - 23rd with 4.00" to 8.00" measured from heavy thunderstorms from the Mt Pleasant area, east across Bay City into Midland. Extensive flooding occurred; resulting in pushing-up the Tittibawassee and Chippewa Rivers to record levels. By the end of June; Saginaw reported nearly eleven inches /10.76"/ of rain for the month which established a new heaviest rainfall record for the month of June - and the second heaviest rainfall ever recorded for any month. The record wettest month /16.16"/ occurred during the widespread flooding of mid- Michigan in September 1986. I wrote an in-depth article on the major flood event here.
On the flip side; while flooding rains fell over the extreme north early in the summer; a gradual rain deficit grew over the central and southern areas. As shown in rain statistics at the climate stations in Southeast Lower Michigan below, both Detroit and Flint ended the summer with a deficit in rainfall (see table). The majority of this below normal rainfall occurred from the southern Metro Detroit area, west southwest across Ann Arbor into the Jackson region.
Percent of Normal Rainfall for the Summer of 2017
When rains did fall over the entire region; frequently they were heavy convective rains with long periods between them of little, if any rain. Perhaps no place did this show up more than the drier areas shown where only 50 to 100% of normal rain fell. Meanwhile; sufficient to surplus rains of 100 to 150% of the normal occurred over the far northern areas.
Years ago /1997/; I did a local study for the metro Detroit area researching; the likelihood of dry spells during the summer. As a resident of metro Detroit since birth; one of many things I noticed about our local climate was the frequent occurrences of dry spells in the summer.
Basically I found out the following:
"FIRST...THERE MUST BE SOME GENERAL DEFINITION OF A "DRY SPELL" INCLUDING RAINFALL AND DURATION. HERE...CLIMATIC STATISTICS OF THE AREA SHOULD BE THE GUIDE. THEREFORE...A DRY SPELL IN SUMMER DURING THE PAST 30 YEARS COULD BE DEFINED AS...LIGHT AMOUNTS OF RAIN (.50 OR LESS) FALLING ON ONLY A FEW OF DAYS IN A PERIOD OF GENERALLY 2 TO 4 WEEKS. THIS IS OPPOSED TO THE MORE SEVERE "DROUGHT" WHICH IS MORE PRONOUNCED IN BOTH RAINFALL DEFICIENCY AND DURATION. IN THE PAST 30 YEARS USING THIS DEFINITION...NEARLY 9 OUT OF 10 TIMES (OR 87% OF THE TIME) SOUTHEAST LOWER MICHIGAN EXPERIENCED A NOTABLE DRY SPELL SOMETIME DURING THE SUMMER MONTHS. THUS...IT IS UNUSUAL NOT TO HAVE A DRY SPELL IN THE SUMMER".
As you can see; this is very common and again materialized this summer. The most notable extended from portions of metro Detroit; west southwest across Ann Arbor into the Jackson region. This region had two notable dry spells using Detroit Metro Arpt /DTW/ stats and the map displayed. Not only is the dry spell important but when it occurs; especially for gardeners and farmers. Both dry spells occurred at the arguably the worst times for plant/water interests. Between May 30th to June 22nd (over three week period); less than half inch /.45"/ fell at DTW. Of course, amounts in the area displayed can be more or less but historically, DTW represents the region. I don't have to tell gardeners nor farmers of the importance of adequate rains needed for newly planted seeds, plants and crops. In addition; this coincides with sun riding high in the sky (near or at the solstice). The second dry spell befell the same area from July 16th through August 10th when sufficient rains are certainly needed for proper growth and maturity. During this nearly 4 week period only about a third of an inch /.36"/ of rain fell. This also is generally the warmest time of of the summer. Even at Flint which was closer to normal rains; a distinctive dry period extended from May 25th through June 16th when only a half inch /.49"/ fell. It would be remiss of me if I didn't mention the normal or average rains during each of the summer months are generally around 3.00 - 3.50" for a summer total 9.00-10.00".The mid July to early August dry spell which took place this summer was found to be the second most common in the study. The most common dry period fell from mid August to early September. Thus far, this September continues to dry trend overall with all areas already having a deficit of two to three inches! A reversal of fortunes, so to speak, has occurred with now the far northern areas the driest this month.
Summer Temperatures and Rainfall Statistics
| DTW - DETROIT v | FNT - FLINT v | MBS - SAGINAW v |
| Temp Ave: 72.4/+0.7 | Temp Ave: 68.7/+0.9 | Temp Ave: 69.6/+1.1 |
| Pcpn Tot: 8.37/-1.52 | Pcpn Tot: 9.26/-0.31 | Pcpn Tot:14.52/+5.65 |
| SE MICHIGAN > | AVE TEMP: 70.2/ +0.9 |
SUMMER TEMPERATURE MAPS
SUMMER RAINFALL MAPS
MONTHLY TEMPERATURE AND RAINFALL DEPARTURES
JUNE
JULY
AUGUST
SEVERE WEATHER: LIMITED
While most people will be glad to see this; severe weather buffs already know - severe weather occurrences thus far in 2017 have been pretty limited or scant. Yes, to put it bluntly it's been rather boring. Up through the third week in September; only 50 severe weather warnings have been issued by the NWS DTX in White Lake for all of Southeast Lower Michigan. This is the second lowest thus far this year using the improved Doppler 88-D radar since 1995.. Interestingly; just last year was the lowest since 1995 with only 42 warnings issued (note; this is not events). In addition; only one tornado has occurred in Southeast Michigan thus far this year when a weak, small /EF-0/ tornado formed on August 17th near Kingston in Tuscola County
So why has it been an uneventful year; especially when you note that other areas around us have higher amounts of warning and events? The main reason was timing of potential severe weather which limited instability. Most potential for severe weather was squashed because the pre-frontal storms either had weakened in the overnight hours to our west - or most new storm development just started to juice up for severe weather either over SE Michigan or east of us.
Summer Outlook Performance?
So, looking back to the opening of summer; How did the Summer Outlook perform? Really pretty good on both temperatures & rainfall expectations and pattern recognition.
From the Outlook -
TEMPERATURES
I look for overall normal temperatures during the summer with any "heat waves or warm periods" to be routinely tempered by cooler air pushing south out of Canada. I'm looking for an occasional -NAO to help deliver the cooler weather as discussed in Hemispheric Patterns below and in the Analogue section. On specific temperature departures; I expect temperatures to average from +1.5 to -1.5 of normal.
Departure: +0.9
RAINFALL
Latest model and atmospheric trends agree with Summer Analogues for generally below normal rainfall this summer as heaviest rains generally fall west and southeast/east of the region. Of course; there will be pockets of heavier rains with convective activity but overall, below normal rains are expected.
More than half the region saw less than 100% of their average summer rainfall (see stats and maps). There were indeed pockets of heavier rain over the northern areas as mentioned above.
| DTW - DETROIT v | FNT - FLINT v | MBS - SAGINAW v |
| Temp Ave: 72.4/+0.7 | Temp Ave: 68.7/+0.9 | Temp Ave: 69.6/+1.1 |
| Pcpn Tot: 8.37/-1.52 | Pcpn Tot: 9.26/-0.31 | Pcpn Tot:14.52/+5.65 |
| SE MICHIGAN > | AVE TEMP: 70.2/ +0.9 |
Autumn 2017 Signs and Remainder Outlook:
The Autumn jet pattern has become more active across the country as September's jet evolved into amplified ridges and troughs taking center stage. Abnormally cool weather across the Great Lakes shifted to record heat! Looking out to analogue Neutral-weak La Ninas suggest more of the same. Neutral to weak La Nina falls generally contain normal to above normal average temperatures on the whole but with moderate to strong fluctuations in temperatures...both warm and cold. This is not an atypical pattern with the majority our falls but these changes generally are more exaggerated with the expected pattern since there usually is less effect from the Pacific (as opposed to El Nino). Therefore, meridional jet air masses can "do their thing" without much hindrance from a Pacific zonal jet to diffuse their effects. (The term "meridional is used in meteorology such as "meridional wind flow" (a.k.a. meridian) or "in the north–south direction" as opposed to zonal or west to east flow.
Therefore, for the remainder of Autumn...
Temperatures should average normal to above but with more significant swings.
Precipitation patterns continues to intimate dry and wet periods but with a sided preference for normal to below normal precipitation continuing to hold sway.
Killing frost and freezes which normally arrive by mid-late October should be on time due to the amplified jet. First sight of snow (trace) usually comes around Halloween into early November - with measurable later in November. I don't see any reason to deviate from that at this time.
Notable Dates:
Halloween - Tuesday 10/31/17Thanksgiving - Thursday 11/24/17
Christmas - Monday 12/25/17
New Years - Monday 01/01/18
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