Don't Panic! You'd Never Know it by the Weather But Climatological Summer is Already Half Over; Now What about the Second Half?

The first six weeks of summer are in the books (and you couldn't prove it by me) but where have been all the typical hot days of summer? Even though June averaged around normal; the notably cool July thus far with temperatures averaging 2 - 4 degrees below normal has certainly taken a bite out of the heat! In addition, only ONE 90 degree day has been officially registered at Detroit - in June no less; (none, officially at Flint nor Saginaw). This has made it seem like we have been in a perpetual June pattern for weeks, not dead-center summer or what if typically called the Dog Days of summer.

"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:

Summer 2015

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***
	Coldest		Warmest		Coldest		Warmest		Coldest		Warmest
	Temp	Year	Temp	Year	Temp	Year	Temp	Year	Temp	Year	Temp	Year
1	66.5	1915	74.8	2012	65.4	1992	74.2	1933	64.8	1915	73.0	1931
2	67.0	1992	74.8	2005	66.1	2009	74.0	1934	65.1	1992	72.9	1933
3	67.3	1927	74.5	1995	66.2	1958	72.7	1936	65.5	1982	72.5	1955
4	67.5	1875	74.5	1955	66.3	1960	72.6	1939	65.8	1945	72.3	1995
5	67.6	1903	74.4	2011	66.5	1969	72.6	1931	65.9	1950	72.1	1930
6	67.8	1985	74.4	2010	66.6	2004	72.6	1921	65.9	1924	72.1	1921
7	67.9	1912	74.2	1988	66.7	1985	72.3	2010	66.1	1985	72.0	2012
8	67.9	1907	74.0	1933	66.8	1972	72.3	1949	66.4	2009	72.0	2010
9	68.1	1982	73.8	1949	66.8	1967	72.2	1955	66.4	2004	72.0	1937
10	68.2	1972	73.7	1921	66.9	1962	72.0	1935	66.4	1979	71.9	1988
11	68.3	1979	73.6	1952	66.9	1927	71.9	2011	66.5	1977	71.9	1936
12	68.3	1902	73.5	1991	67.0	1982	71.9	1938	66.6	1951	71.7	1998
13	68.3	1891	73.5	1959	67.0	1950	71.8	1988	66.8	1946	71.5	1934
14	68.4	1889	73.5	2002	67.1	1965	71.7	2012	66.9	1965	71.5	1932
15	68.5	1883	73.5	1931	67.1	1945	71.7	1995	66.9	1962	71.4	2011
16	68.7	1917	73.2	1944	67.2	1997	71.7	2002	66.9	1917	71.4	1959
17	68.8	1924	73.0	1987	67.4	1951	71.7	1987	67.0	1958	71.2	1973
18	68.8	1904	73.0	1919	67.4	1957	71.6	2005	67.0	1926	71.2	1949
19	68.9	1967	72.9	1953	67.4	1924	71.6	1983	67.2	1972	71.2	1919
20	69.1	1897	72.9	1930	67.5	2000	71.3	1944	67.3	1981	70.9	2005
* 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

JUNE

 JULY 1-14

 

While heat has been lacking this summer thus far, rainfall has NOT; especially across the southern counties of Southeast Lower Michigan!

RAINFALL                         

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.

 

Rainfall:

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!

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

NICE AND BRIGHT TO BLACK AS NIGHT; THE 35th ANNIVERSARY OF THE JULY 16TH, 1980 DERECHO

Step back in time on the 35th anniversary of one of the most notable derechos ever to clobber Southeast Lower Michigan from Ann Arbor into Metro Detroit; The July 16th 1980 Derecho! With the numerous severe weather outbreaks along with the severe winter weather of the mid 1970s to early 80s; I was fast becoming a seasoned veteran to rough weather in Southeast Lower Michigan during my formative years with the National Weather Service.
 

NICE AND BRIGHT TO BLACK AS NIGHT!

THE JULY 16TH, 1980, DERECHO

Written by: William R. Deedler, Weather Historian

Originally written:
July 22nd, 2005/Updated July 2015

 

The word "derecho" may sound unfamiliar or its use in meteorology relatively recent in nature, but the word actually was brought into meteorological vernacular way back in 1888. Dr. Gustavus Hinrichs, a physics professor at the University of Iowa, was given that credit when he used the word, derecho, in a paper he had published in the American Meteorological Journal in 1888. Dr Hinrichs chose this terminology for thunderstorm induced straight-line winds as an analog to the word tornado. Derecho is a Spanish word which can be defined as "direct" or "straight ahead" while tornado is thought by some, including Dr. Hinrichs, to have been derived from the Spanish word "tornar" which means "to turn". This definition and other derecho facts are taken from the Storm Prediction Center's About Derechos web page, which contains many interesting facts and background studies about derechos.

Even though the term "derecho" dates back well over a century, it has only been relatively recent (since the 1980s) that more investigative studies and research has greatly increased our knowledge about these types of storms. Derechos are associated with a line of showers or thunderstorms that are often "curved" in shape on radar and satellite. These bowed out storms are called "bow echoes". A derecho can be associated with a single bow echo or multiple bow echoes. By definition winds in a derecho must meet the National Weather Service criterion for severe wind gusts (greater than 57 mph) at most points along the derecho path. In the stronger derecho events winds can exceed 100 mph.

Southeast Lower Michigan has had several derechos in the past, but certainly one of the more memorable ones plowed through extreme Southern Michigan during the forenoon hours of Wednesday, July 16th, 1980.

Summer of '80 starts out on a chilly note

The Summer of 1980 actually hadn't been much of a summer as far as warm temperatures and dry weather were concerned. The summer had been unseasonably cool and soggy into early July. June's average temperature was a relatively chilly 63.7 degrees, making it the eighth coolest June on record at Detroit. To add insult to injury, not only had June been cool, it also had been very wet. June's monthly rainfall totaled up to nearly six and a half inches /6.42"/, making it the sixth wettest June on record, which undoubtedly made the month seem even worse.

While the first few weeks of July averaged a bit below normal, some good ole' fashion summer-time heat finally began to bubble up into the region by mid month. Hot and unstable air pushed its way north into the Great Lakes by the 15th as temperatures surged into the lower to mid 90s. Up until that time, only once before had temperatures pushed up into the 90s that summer. The arrival of the hot and humid air mass set off some scattered showers and thunderstorms on the 15th, but really nothing of consequence compared to what would generate to the west overnight.

Birth of a Hybrid Derecho 

 

The low pressure area with attending warm and cold fronts pushing through the Upper Midwest (see above map) was responsible in igniting the derecho at the surface late on the 15th. Thunderstorms developing over extreme Eastern Iowa and Northern Illinois during the very early morning hours of the 16th, intensified and formed into a squall line that pushed through Northern Illinois between 3 AM and 5 AM EDT. The storms were spawned out ahead of the frontal system as it approached northern Illinois, mainly ahead of the triple point juncture and nearly perpendicular to the warm front. At the same time, a potent mid level short wave and wind max (approx 60-70 knots) surged east across the Upper Midwest toward the Southern Great Lakes.

Nice and Bright to Black as Night

The derecho surged quickly east across Northern Indiana and Southern Lake Michigan with a measured wind gust of 98 mph at the St. Joseph Coast Guard as it blasted onshore in Southwest Lower Michigan! While the sky was relatively bright at sunrise over Southeast Lower Michigan, a band of foreboding clouds advanced in quickly from the west, covering the celestial dome. As the forceful storms and associated hurricane force winds approached the area, several observers remarked about the horrid dark green color the sky took on as the squall moved overhead. In fact, numerous people over the years have commented about the "dark pea green sky" that accompanied the July 16th 1980 storm. The green color in the sky may have been reflective of the low sun angle at the time (the derecho moved through region between 730 and 930 AM EDT) and abundance of moisture in the low clouds. It got so dark that many street lights were triggered and popped on over portions of the region. Severe thunderstorm warnings were issued over the region though some remarked: "it happened so quickly and early in the day, it caught us off guard".

The hardest hit regions across Southeast Lower Michigan were Washtenaw and Wayne counties, extending mainly from the Ann Arbor area east into southern sections of Detroit (or south of the Ford Road /M-153/ corridor). While the wind officially gusted to 71 mph at Detroit Metro Airport, much higher winds were reported in other areas in the strongest core of the derecho.

As one person who witnessed the swath of damage across southern portions of Washtenaw and Wayne counties, the following excerpts from storm data relay the incredible outcome of the storm. In the storm data below, the derecho is referred to as a downburst. In addition, the derecho was accompanied by a small tornado as it exited extreme Southeast Lower Michigan. Tornadoes can occur in isolated thunderstorm supercells ahead of the derecho producing squall line or they may be associated with the squall line itself.

STORM DATA
Counties in SE Mich	Date 7/16/80	Time 830-920AM EDT
Washtenaw Wayne Monroe	"Intense downburst developed just west of Ann Arbor. Path of the most intense damage across southern Ann Arbor then eastward through the Downriver suburbs of Detroit. Winds estimated up to 100 mph in Washtenaw county, up to 150 mph in Wayne County. Innumerable buildings, vehicles and trees destroyed in eastern Washtenaw, central and southern Wayne, and northeastern Monroe counties. Several boats were swamped on the Detroit River. Power off in some areas up to ten days."
Downriver Communities	Date 7/16/80	Time 910 AM EDT
Allen Park, Lincoln Park, and Ecorse, in Wayne county	"Railroad cars blown off track in both directions in Allen Park. Department store roof blown sideways in Lincoln Park. Funnel sighted over Detroit River from Canadian shore. Tornado damage included in, and hardly distinguishable from large area of straight line wind damage. Funnel continued eastward several more miles into Canada".

It's amazing that after reading about the force of the wind and subsequent damage, that only one person - a woman - was reported injured in sort of a freak accident when the wind forced her into a revolving door! Note the following that was taken from "Derecho Hazards in the United States" by Walker S. Ashley, Climatology Research Laboratory at the University of Georgia, Athens, Georgia. It gives an interesting account of the July 16th,1980 Derecho storm damage relative to other storm damage.

Fujita and Wakimoto (1981) provided extensive documentation of the 16 July 1980 derecho that produced widespread damage across large areas of Michigan, Illinois, Wisconsin, and Minnesota. They indicated that this storm produced approximately $650 million in damage as it traversed the four-state region. Accounting for inflation (to 2003 dollars), this storm produced an estimated $1.3 billion in damage from strictly straight-line winds. This estimate exceeds many damage tallies from U.S. hurricanes and is larger than the inflation-adjusted damage estimates from all major tornadoes that have affected the U.S. since 1890 (Brooks and Doswell 2001). This single event illustrates that derecho damage can exceed the damage from most hurricanes and tornado events affecting the contiguous U.S.

Note the graph above which displays monthly damaging wind events in the U.S. July and June are the top months for wind storms. Many of these wind storms occur as derechos over the Great Lakes states (Johns and Hirt, 1987).


Look for an excellent detailed paper on the Derecho of July 16th 1980 by Dr. Fujita in 1981 here

Detroit Climate Observation for July 16th, 1980

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

Grand Daddy of all Southeast Michigan Heatwaves!

THE "GRAND DADDY" OF SOUTHEAST MICHIGAN HEAT WAVES 

                                             July 8th - July 14th, 1936

 (originally written in the late 1990s with updates 2013)

Written by: William R. Deedler, Weather Historian 

 

Though heat waves or hot spells generally occur nearly every summer, no heat wave compares in intensity nor in duration than the heat wave that occurred across Southeast Lower Michigan in the summer of 1936. For many of us, it was when our grandparents were in their young or middle-age adult years. Little, if any, exaggeration would accompany their tales of the oppressive heat experienced sixty years ago, back in July 1936.

The last week of June into the first week of July 1936 was quite variable with afternoon highs ranging from around 70 to near 90. Evidently, weather patterns were quite progressive. After a day or two of heat build up, a cold front would push through the area and sweep the heat to the south and east on a regular basis. A change in the weather pattern was heralded by a strong but dry warm front that pushed across the area midday on July 6th. Very warm air rushed north into Southeast Lower Michigan, causing the mercury to rise up to near 90 on the 7th, but this was merely a hint of the heat to come.

On the afternoon of the 8th, the temperature soared to just shy of 105 (104.4) degrees and thus, the unprecedented heat was on. For the next seven consecutive days, the mercury would "bubble" above the 100 degree mark (see Table 1). The oppressive heat was compounded by humidity levels generally ranging in the 30s and 40s during the afternoon hours. While those levels are relatively low any other time, when combined with temperatures 100+, the heat index or, how hot it really felt, ranged roughly from 110 to 130 degrees. Little, if any relief was found during the evening hours into midnight with temperatures ranging from the mid and upper 90s at the start (6 to 7 pm) to hovering still in the mid 80s at midnight. For a few hours before dawn, overnight low temperatures "cooled" into the mid 70s. Desert-like conditions were exaggerated by the non-existence of rain. The thirst of the parched land was left un-quenched as not one drop of rain was officially recorded at the Detroit downtown office through the period.

Since this was 1936, the residents of Southeast Lower Michigan did not have the luxury of air conditioned homes, businesses or shopping malls to take refuge from the heat. Most people had to make do with the old standbys such as fans, blocks of ice from the Ice Man (the Ice Man cometh') or maybe by just taking a swim. While other heat waves in Southeast Lower Michigan have lasted longer, none had been longer accompanied by the fierce heat of this one. I was unable to find any documentation of heat related deaths (I'm not sure it was even done at this time), but with this intense of a heat wave, I'm sure there were cases.

The break in this torturous heat wave came without fanfare (storms). Not even a shower was noted in the log. Looking at the observations on the 14th...the wind shifted from the southwest to the northwest and then to the northeast. A lot of the characteristics of a "backdoor" cold front pushing south- southwest out of southern Canada. Occasionally these fronts will come through dry with an abrupt wind shift and falling temperatures. The temperatures fell from 104 at 200 pm...to 85 at 400 pm to a relatively chilly 69 by midnight. The heat wave started with a 104 degree reading on the 8th and ended with the same on the 14th. The first drop of rain was long in coming and not observed until a measly .08 fell on the 23rd.

Table-1 - Summary of the daily highs, lows and resultant means
-------   for July 8th - 14th, 1936 in Detroit, Michigan.
         
           Date          High      Low       Mean
                       
         July  8th       104 *      72        88
                  
         July  9th       102        75        89
                                    
         July 10th       102        77        90 **
                                    
         July 11th       101        77        89 
                                    
         July 12th       100        76        88 
                                    
         July 13th       102        73        88
                                    
         July 14th       104        69        87
                                                        
              *  Second highest all time temp 
              ** Second highest all time mean

Another, very notable heat wave that baked the area for a longer period of time but was not quite as hot, occurred in the late summer of 1953 from August 26th - September 3rd. An eleven day string 90 degrees or better, cooked the area. What's worse, nine of those days were 95 degrees or higher, with two of those hitting the century mark. Those two 100 degree days occurred near the end of the heat wave on September 2nd and 3rd, and with the exception of one other day, were the latest 100 degree days ever reported in Detroit (the latest 100 was also back in the "dust bowl" 1930s, on September 15th, 1939). Still another heat wave, in the Summer of '64, was one day longer (12) than the one in 1953 and has the "honor" of the longest heat wave on record when looking at just consecutive days of 90 degrees or greater. This heat wave extended from July 17th - 28th, 1964. There were no 100 degree days during this period, with the highest temperature being "only" 95.

On a more recent note and better in the memory of Southeast Lower Michiganders, is the hot summer of 1988, when a record amount of 90 degree or better days, 39 to be exact, produced one hot, sultry summer. The previous record was 36 days which again, occurred in "dust bowl 30s" (1934) when also, the hottest temperature of all time, (105 July 24th, 1934), occurred in Detroit. In addition to the record amount of 90 degree days in 1988, we topped the 100 mark 5 times, with the highest at 104 on June 25th. We missed the all time high by just a degree, but for those who remember, a hot, desert-like wind blew across the area that day as dew points dropped into the lower 60s, and humidities fell into the 20s.

That memorable summer of '88 became the seventh hottest summer (Jun-Aug) ever recorded in Detroit with a average of 74.2 (see updated listings below). The fourth hottest summer goes to 1955, with an average of 74.4 degrees. During that hot summer, the month of July set the record for days of 90 degrees or greater in a month with 17. This was the primary reason why July 1955 became second hottest month ever in Detroit, with a average temperature of 79.1. Last July (2012) superseded that temperatures with 79.3 for Detroit's hottest July. We now come to our hottest summers, at least in the last 142 years (1870). The "gold" medals goes to 1995 and again,  just last year in 2012! That's right, just last year during the 3 month summer period (Jun-Aug), Detroit averaged 74.5 degrees helped tremendously by the hottest July. Strangely enough though, back in July 1995 that July didn't even place in the top 10 hottest months. The hot month in the Summer of '95 was August, with an average temperature of 77.1, making it the hottest August on record. June 1995 placed in at the eleventh hottest.

Here is the updated top 7 Hottest/Coldest Summers on record at Detroit, Flint and Saginaw. Several of our recent summers have entered the record books for heat and changed previous rankings, especially at Detroit.

Top 20 Coldest/Warmest Summers 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	66.5	1915	74.8	2012	65.4	1992	74.2	1933	64.8	1915	73.0	1933
2	67.0	1992	74.8	2005	66.1	2009	74.0	1934	65.1	1992	73.0	1931
3	67.3	1927	74.5	1995	66.2	1958	72.7	1936	65.5	1982	72.5	1955
4	67.5	1875	74.5	1955	66.3	1960	72.6	1939	65.8	1945	72.3	1995
5	67.6	1903	74.4	2011	66.5	1969	72.6	1931	65.9	1950	72.1	1930
6	67.8	1985	74.4	2010	66.6	2004	72.6	1921	65.9	1924	72.1	1921
7	67.9	1912	74.2	1988	66.7	1985	72.3	2010	66.1	1985	72.0	2012

---

The Deadly Summer Heat

Written by: Jeff Boyne - National Weather Service La Crosse Wi

 

In a normal summer, about a 175 Americans die as a result of the taxing effect that excessive heat and humidity can have on the body. In a disastrous heat wave of 1980 more than 1,250 people died in St. Louis, Missouri. Just last summer, Chicago experienced its worst weather-related disaster with 465 heat related deaths recorded during the period from July 11-27.

How Heat and Humidity Affects the Body:

The human body gets rid of excessive heat (above 98.6 F) by increasing the rate of the blood circulation. This causes the blood vessels to expand to accommodate the increased flow. The tiny blood capillaries in the upper layers of the skin are also put into operation. By doing this, the blood is able to circulate closer to the skin's surface and the excess heat in the body is able to be dispensed into the cooler atmosphere surrounding the body.

At the same time, water diffuses through the skin from the sweat glands in the form of perspiration. Sweating, by itself, does nothing to cool the body. Evaporation of the perspiration must take place in order for the process of sweating to be of any use. When perspiration evaporates, it takes some of the excess heat away from the body; thus, the body is cooled.

If high humidity accompanies the hot temperatures, the body will have a very hard time cooling itself down, because the perspiration on the skin will not evaporate off of the skin. As a result, the body will continue to try to cool itself down by sweating. This will not only cause the body to lose water, but it will also lose salt. If the body cannot cool itself down or if it loses too much salt, one of the following three heat disorders will result in the table-2 below.

Table-2 3 Types of Heat Disorders
HEAT DISORDER	SYMPTOMS	FIRST AID
Heat Cramps	Painful spasms usually in the muscles of the legs and abdomen. Heavy sweating.	Get the person to a cooler place. If the victim has no other injuries and can tolerate water, give one- glassful every 15 minutes for an hour.
Heat Exhaustion	Heavy sweating, weakness, skin cold, pale and clammy. Pulse thready. Normal temperature possible. Fainting and vomiting.	Get the person out of the heat and and into a cooler place. Have them lie down on their back and elevate their feet with something. Either remove or loosen the victims clothing Cool them by fanning and applying cold packs (putting a cloth between the pack and the victim's skin) or wet towels or sheets. Care for shock. Give the victim one-half glassful of water to drink every 15 minutes, if they can tolerate it. These first aid steps should bring improvement within a half hour.
Heat Stroke	High body temperature (106 F or higher). Hot, dry skin. Rapid and strong pulse. Possible unconsciousness	Heat stroke is a life-threatening situation. Call 911. Get the person out of the heat and into a cooler place. Cool the victim fast. Immerse them in a cool bath, or wrap the wet sheets around their body and fan it. Care for shock by laying the victim on their back and elevate the feet with something Wait for medical help to arrive. Also do not give anything by the mouth.

The most susceptible people to the above heat disorders are the very young, very old, chronically ill, overweight, those who work in hot places, and athletes. Studies indicate that, other things being equal, the severity of heat disorders tends to increase with age. Heat cramps in a 17-year old may be heat exhaustion in someone 40, and heat stroke in a person over 60.

The Heat Index:

This index is used to alert the public how hot it really feels when the Relative Humidity is added to the actual air temperature. These values were devised for shady, light wind conditions.

Table-3 Heat Index (or Apparent Temperature) Chart

Heat Index

		Relative Humidity (%)
		40	45	50	55	60	65	70	75	80	85	90	95	100
A	110	136
i	108	130	137
r	106	124	130	137
	104	119	124	131	137
T	102	114	119	124	130	137
e	100	109	114	118	124	129	136
m	98	105	109	113	117	123	128	134
p	96	101	104	108	112	116	121	126	132
e	94	97	100	103	106	110	114	119	124	129	136
r	92	94	96	99	101	105	108	112	116	121	126	131
a	90	91	93	95	97	100	103	103	109	113	117	122	127	132
t	88	88	89	91	93	95	98	100	103	106	110	113	117	121
u	86	85	87	88	89	91	93	95	97	100	102	105	108	112
r	84	83	84	85	86	88	89	90	92	94	96	98	100	103
e	82	81	82	83	84	84	85	86	88	89	90	91	93	95
(°F)	80	80	80	81	81	82	82	83	84	84	85	86	86	87

With Prolonged Exposure and/or Physical Activity
Extreme Danger	Danger	Extreme Caution	Caution
Heat stroke or sunstroke highly likely	Sunstroke, muscle cramps, and/or heat exhaustion likely	Sunstroke, muscle cramps, and/or heat exhaustion possible	Fatigue possible

*Editor's note: 7/11/13
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.

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