Summer Dry Spells in Southeast Michigan

The latest dry spell affecting some in Southeast Michigan reminds me
of an article I wrote back in the late '90s. While working with the NWS, like anywhere else, I noticed numerous patterns and trends in our weather that would repeat over time.  I researched and wrote about many weather events and trends. The following article (originally written in 1997) was about one such pattern.

...SUMMERTIME DRY SPELLS IN SOUTHEAST LOWER MICHIGAN ARE MORE COMMON 
THAN YOU MIGHT THINK... 

WRITTEN BY: WEATHER HISTORIAN BILL DEEDLER NWS WHITE LAKE MI 

THE RECENT DRY SPELL THAT MOST OF THE AREA HAS SEEN THIS JULY IS
FAIRLY COMMON ACROSS SOUTHEAST LOWER MICHIGAN. IN FACT...IT IS RARE
NOT TO HAVE A NOTABLE DRY PERIOD DURING THE SUMMER MONTHS (JUN-AUG). 
LOOKING BACK AT THE LAST 30 YEARS (1967-96) CLIMATIC STATISTICS IN 
DETROIT SHOWED SOME INTERESTING AND SOMEWHAT SURPRISING DRY SPELL 
TRENDS.

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. THE YEARS THAT SHOWED NO SIGNIFICANT 
DRY PERIOD IN THE SUMMER WERE...1972...1977...1987 AND THE COOL SUMMER 
OF 1992. IT IS INTERESTING TO NOTE...THESE "WET" SUMMERS WOULD HAVE COME 
EXACTLY EVERY 5 YEARS SINCE 1972 IF THE AUGUST OF 1982 HAD NOT HAD A 
PRONOUNCE DRY SPELL. SOME MONTHS DID END UP WITH SIGNIFICANTLY LESS 
THAN NORMAL RAINFALL BUT DID NOT FALL IN THE DRY SPELL CATEGORY BECAUSE 
THE RAINFALL WAS FAIRLY EVENLY DISTRIBUTED.

NEARLY TWO THIRDS OF THE TIME WHEN A DRY SPELL OCCURRED...IT WAS THE 
ONLY DRY SPELL THAT SUMMER. THE OTHER THIRD OF THE TIME...WHEN THERE 
WAS ONE DRY SPELL...ANOTHER FOLLOWED LATER IN THE SUMMER. ONE OF THE 
MORE SURPRISING AND NOTABLE ITEMS TO COME OUT OF THIS BRIEF STUDY WAS 
THE SHIFTING OF THE DRY SPELLS OVER THE YEARS. FROM THE MID 1960S 
THROUGH THE 70S...IT WAS UNHEARD OF TO HAVE A NOTABLE DRY PERIOD IN 
JUNE. AT THE SAME TIME...9 OUT OF THE 13 AUGUSTS (1967-79) HAD ONE OR 
MORE DRY SPELLS WITH JULY ABOUT HALF AND HALF. YET IN THE 1980S AND 
EARLY 90S...THE REVERSE TOOK PLACE. THE DRY SPELLS SHIFTED BACK INTO 
EARLY TO MID SUMMER WITH ONLY TWO YEARS (1982/83) HAVING A DRY SPELL
IN AUGUST. SINCE 1994...DRY SPELLS IN AUGUST HAVE BEGUN TO REAPPEAR. 
AUGUST 1996...FOR INSTANCE...WAS THE FOURTH DRIEST ON RECORD IN
DETROIT SINCE 1872 WITH ONLY .43 OF RAIN FALLING (NORMAL 3.43).

LOOKING AT EACH MONTH INDIVIDUALLY...THE DRY PERIODS IN JUNE HAVE
BEEN ALMOST EXCLUSIVELY MID TO LATE MONTH...WHILE IN JULY THEY
OCCURRED AT ALMOST ANYTIME AND IN AUGUST...THE PREFERENCE WAS AGAIN
MID TO LATE MONTH AND FREQUENTLY LASTED INTO SEPTEMBER. WHILE THESE
DRY SPELLS CAN OCCUR AT ANYTIME DURING THE SUMMER...THE CHANCES 
GRADUALLY INCREASE AS THE SUMMER EVOLVES. THE BEST CHANCE FOR A DRY 
SPELL HISTORICALLY IS FROM MID AUGUST INTO EARLY SEPTEMBER WITH MID 
JULY TO EARLY AUGUST A CLOSE SECOND.

ONE OF THE MORE MEMORABLE EXTENDED DRY PERIODS IN RECENT TIMES
OCCURRED DURING THE HOT SUMMER OF 1988. DROUGHT OR NEAR DROUGHT 
CONDITIONS DEVELOPED LATE IN THE SPRING AND CONTINUED UNTIL MID JULY. 
FROM LATE MAY INTO THE THIRD WEEK OF JUNE ONLY .39 RAIN FELL IN 
DETROIT. THEN ANOTHER VERY DRY PERIOD TOOK PLACE FROM LATE JUNE INTO 
MID JULY WHEN ONLY .04 FELL. THIS DESERT-LIKE ATMOSPHERE...AS MOST 
INHABITANTS OF THE AREA CAN ATTEST...WAS OFTEN ACCOMPANIED BY DESERT- 
LIKE TEMPERATURES. MAY OF 1988 WAS THE THIRD DRIEST MAY (.87) ON RECORD 
IN DETROIT...WHILE JUNE WAS THE SECOND DRIEST JUNE (.97). THIS ARID 
CLIMATE CAME AT THE WORST TIME POSSIBLE...EARLY IN THE GROWING SEASON 
...A TIME WHEN CONVECTIVE RAINS NORMALLY BEGIN.

OTHER DRY MONTHS NOTED WERE...JUNE 1984 (1.04)... JULY 1974 (.59) 
...JULY 1984 (.95) AND AUGUST 1982 (.72). THE LEAST AMOUNT OF RAIN
EVER RECORDED IN DETROIT DURING A SUMMER MONTH WAS A MEAGER .16
IN AUGUST 1894. THE SECOND HIGHEST AMOUNT OF RAIN IN A SUMMER MONTH 
ALSO OCCURRED IN AUGUST...AUGUST 1926 WITH 8.33 INCHES (JULY 1878
WAS THE HIGHEST WITH 8.76). CLEARLY...THE SUMMER MONTHS CAN BE
"FEAST OR FAMINE" WHEN IT COMES TO RAIN.

Dry/Drought map for SE Michigan as of 7/19/11. Note this is a broad scale average and

not fine tuned to a local areas. 

---

Grand Daddy of all Heatwaves!

The Grand Daddy of all Heatwaves in Detroit!
(originally written in the late 1990s)

*Editor's note:
I wrote the above article in the late 1990s. At the time, 1964 looked to be the longest streak BUT an 89 degree high occurred at DET City Arpt during the hot stretch (checked DET to DTW), In 1964, DET WAS the official site...so it can't be used...DTW Metro Arpt became the official site in April 1966. Funny what a problem a digit can cause (and it WAS 90 at DTW so it was hot anyway)!

The 1953 hot and miserable streak IS the longest heatwave with the Grand Daddy of all Heatwaves in Detroit in 1936 with the hottest and most miserable streak of days above 100 degrees. The all time hottest day at Detroit though was 105 back on July 24th, 1934. Back in the hot summer of 1988 we almost tied that with a 104 on June 25th 1988!

Before I retired, I went over all of Detroit's records and caught a few other mistakes...some back to the 1800s. Detroit's observation site moved several times in its history.

Bill Deedler

HOT! HOT! HOT!

The strong hot ridge of high pressure mentioned in the previous blog continues to dominate much of the central and eastern portions of the country as of Sunday 7/17/11. This will be the story for much of the week of what could be our hottest week this summer in regards to persistence (let's hope so). High heat indices are expected over a wide area of the country because of the heat AND humidity. Remember heat indices are what is "feels like" with the temperature and humidity combined. Many people are unaware  that heat is the number one weather-related killer in the United States /NWS/.

For projected heat indices for several periods and days out across the country, you want to look at the HOT FUTURE!

For a narrative of recent, present and future heat indices, HOT TIMES!

For local heat indices write ups and current observations, HOT SE MICH!

For an in important write-up on heat safety, check out, HOT SAFETY!

Try to stay cool.

Mid-Summer Update - Boosting Temperatures but Precipitation Variability Remains Intact

On my original Outlook, I was looking for temperatures to average up to 1.0 degree above normal for the summer as a strong ridge over the south-central US routinely battled for dominance the upper cool Canadian Low over eastern Canada. This pattern was the one mentioned and preferred in the Outlook. The Canadian upper air cool downs have become less frequent and notable with time as the upper ridge strength continues to  be impressive as we enter the hottest part of the climatological summer.

From the original Outlook:

Temperatures:
Overall, I look for summer temperatures to average around normal (-.5 to +1.0). Local analogue data for this summer generally shows normal to below normal averages. At the same time, projections for the upper wind pattern suggest ridging over the south-central part of the country will periodically expand into the Great Lakes bringing more heat into the region. The temperature outlook is a tough call and will mainly depend on the how strong the ridge becomes and its placement. At this time, it looks like the ridge will oscillate from just to our west (Midwest) to the eastern third of the country. This will bring periods of heat and cool downs (while working in conjunction with the upper low in Eastern Canada). Number of 90 degree days should be about average for the summer, 8-12.

The preferred pattern has indeed evolved (and then some) and is why I leaned toward an above normal departure (which was against the dominant analogues). The upper air pattern projections continue to show signs of the hot ridge nosing (as of 7/15/11) routinely into the Great Lakes with heat and subsequent humidity much of remainder of July and this looks good. 

I have decided to up my temperature departure for the summer to 1 1/2 to  3 degrees above normal. As far as 90 degree days, I originally went 8-12 days for the entire region. I will also boost that to 11-15 for the Detroit and Flint areas but remain with the original projection for the Saginaw Valley region

Further Out>>>
It will be interesting to see if the pattern of the analogues which showed the cooler (relative to normal) part of the summer coming in the second half. If that does occur, and usually the analogue projections are better at the overall pattern than their numerical departures, then August should contain closer to normal or possibly below temperatures. We shall see. 


Rainfall:
I see no need for precipitation changes as strong variability remains dominant. Some areas have had more than enough rain while others are dry and this is very similar to 2008.
 

Drier pattern becoming more pronounced in some areas

Many areas have not seen any appreciable rain for at least a couple of weeks. While portions of Metro Detroit got clobbered by heavy rains and severe weather on July 2nd (DTW included), other areas remained bone dry. Portions of the northern suburbs, including White Lake /DTX-NWS/, have not seen any decent rain since June 24th. This is NOT the time to go dry and we've seen this problem before. Gardens and crops are hurting for rain in many areas of Southeast Michigan. Here in northern Livonia, we've had a trace of rain since the 24th and the lawns (or should I say hay) where not watered, are reflecting that. The high solar angle and heat have quickly exacerbated the problem.

More heat is on the  docket into early next week with the next chance of rain not looking that promising /11-12th/ as a back door cold front slides out of Canada. These fronts are notorious for wind shifts, cooler more comfortable air but little, if any rain. Our only hope will be if enough moisture can pool ahead of the front and she slides south to encourage instability and rain...but I'm not too hopeful.

Check out this past14 day rainfall map of SE Michigan. Note how some areas have been doused with rain while other have had little or none.

June follows expected overall trend well...warm...dry and wet (depending on location)

All of Southeast Lower Michigan averaged above normal for June and like many other months, it's mainly due to a handful of days. The month on the whole was actually normal to below with a third of the month containing below normal departures. The really uncomfortable heat came from the 4th - 8th with temperatures popping into the 90s three of the five days. The record day of the mini-heatwave came on the 7th when a high of 95 /record/ was attained (Saginaw matched an old record that day with 93). The temperature at Detroit hit 96 on the 8th but this was not a record.

The other thing notable for the month was drier weather surfaced and became much more predominant around metro Detroit south to the border (a big change from the spring). In fact, with just under an inch /.94"/ falling at Detroit Metro, that made it the second driest June on record (and actually a bit drier that the hot and dry June of 1988)!  Severe weather across the region was limited to just a few noteworthy events considering it was June.

Areas from Flint east to the Port Huron and north into Saginaw and Thumb, however, saw normal to above rains. Flooding rains were the big headlines for portions of northern St. Clair county (N-NW of Port Huron).

My call for June was an above normal temperature departure. The average for the selected above normal analogue Junes came in at 70.6 for Detroit. The actual for June 2011 was right on the money...70.6 degrees. 

AVERAGE MONTHLY: 70.6   TOTAL FOR MONTH:   0.94    
DPTR FM NORMAL:   1.6   DPTR FM NORMAL:   -2.61    
HIGHEST:    96 ON  8    GRTST 24HR  0.38 ON 10-10  
LOWEST:     54 ON 15,14

From the Outlook,..

Most striking of the analogue trends is the likelihood of a warmer June (or warm first half of the summer).

 

Taking the average temperature for the above normal Junes in the study (and this was my forecast preference) left an average of 70.6 (see below) In fact, that 70.6 occurred three other times in the five warm Junes! It was the mean, the mode and median...outstanding (and it will never happen again ;-)!

 

1925 70.6
1939 70.2
1971 70.8
1976 70.6
2008 70.6


Rainfall at Detroit was well below normal but that did not tell the whole story across Southeast Lower Michigan. As mentioned above, well above normal rainfalls were seen at isolated locations across the northern half of Southeast Michigan. Notable drier trends were noted over the southern third of the region.

From the Outlook...

The drier part of the summer showed up at different times and not necessarily mid-late which is more common. Overall, I look for near normal  rainfall (locally above in heaviest storms) as the storm track remains active but with a trend toward rainfall events being less often.
One trend that does show up is a somewhat drier pattern materializes  from the wetter springs. I feel we will see both patterns (dry/wet) this summer and thus, around normal in the general call. 
 

July's analogues were decided normal to below in temperatures while precipitation amounts were variable (keeping the June rainfall trend).