7/18/13

Strong Weather Dynamics Likely To Bring Severe Weather Friday Into Friday Night Across Southeast Lower Michigan

Severe Weather Report of July 19th, 2013 
__________________________________________________________________________________________
7/18/13
The miserably hot and humid weather that has plagued Southeast Lower Michigan will come to a climatic end over the weekend as an active cold front pushes its way through the region Friday night into the first half of Saturday. While Saturday will cool off some with lower humidity, the full effects of the cooler air mass won't be felt until Saturday night into Sunday. 

In the meantime until the front makes its way through; strong to severe thunderstorms are possible on Friday with the best chance of organized severe weather later Friday afternoon into Friday night. From the Storm Prediction Center /SPC/ this Thursday morning; 
"NUMEROUS EPISODES OF STRONG TO SEVERE STORMS SEEM POSSIBLE IN THE
GREAT LAKES THROUGH THE DAY WITH THE GREATEST SEVERE POTENTIAL 
COMING IN THE FORM OF DAMAGING WINDS AROUND THE TIME OF MAXIMUM 
DIURNAL HEATING. IN ADDITION TO LOCALLY STRONG INSTABILITY...
STRENGTHENING UNIDIRECTIONAL VERTICAL SHEAR SHOULD CONTRIBUTE TO 
RELATIVELY FAST-MOVING AND LONGER-LIVED LINEAR SEGMENTS WITH SOME
LEWPS AND BOWS RESULTING IN LOCALLY GREATER POTENTIAL FOR DAMAGING 
WINDS AND PERHAPS A BRIEF TORNADO OR TWO."
 
And part of this afternoon's script from SPC;
 
A SHARPLY DEFINED COLD FRONT WILL ADVANCE SEWD ACROSS WI AND THE UPPER 
PENINSULA OF MI BEING POSITIONED FROM LOWER   MI WSWWD ACROSS FAR NRN IL 
INTO IA BY LATE AFTERNOON. THE MODELS SUGGEST THAT THUNDERSTORMS WILL
INITIATE ALONG THE FRONT BY EARLY TO MID AFTERNOON AS SFC TEMPS WARM AND 
MODERATE TO STRONG INSTABILITY DEVELOPS. THE INSTABILITY ALONG WITH LARGE-
SCALE ASCENT ASSOCIATED WITH THE UPPER-LEVEL TROUGH AND MODERATE TO STRONG
DEEP LAYER SHEAR SHOULD BE FAVORABLE FOR SEVERE WEATHER ACROSS MUCH OF THE
GREAT LAKES REGION FRIDAY AFTERNOON AND EVENING. 

FORECAST SOUNDINGS AT DETROIT AND CHICAGO AT 00Z/SAT SHOW MLCAPE
VALUES FROM 2000 TO 3000 J/KG WITH 0-3 KM LAPSE RATES OF 8.0 TO 8.5
C/KM. THIS COMBINED WITH UNIDIRECTIONAL WIND PROFILES SHOULD BE
FAVORABLE FOR A WIND DAMAGE THREAT WITH MULTICELL LINE SEGMENTS THAT
ORGANIZE ALONG THE FRONT. AS STORM COVERAGE INCREASES DURING THE
LATE AFTERNOON...A NEARLY CONTINUOUS LINE COULD ORGANIZE AND MOVE
SWD ACROSS SRN LOWER MI EXTENDING WSWWD INTO NRN IND AND NRN IL
WHERE AN ENHANCED WIND DAMAGE THREAT MAY DEVELOP. DUE TO THE
MODERATE TO STRONG INSTABILITY...ISOLATED LARGE HAIL WILL ALSO BE
POSSIBLE WITH THE MORE INTENSE ROTATING CELLS EMBEDDED IN THE LINE.
ALTHOUGH THE LOW-LEVEL WIND PROFILES ARE FORECAST TO BE
UNIDIRECTIONAL...SUBSTANTIAL SPEED SHEAR IN THE BOUNDARY LAYER IS
EVIDENT ON FORECAST SOUNDINGS. THIS MAY ALLOW FOR A TORNADO THREAT
TO DEVELOP ESPECIALLY IF SUPERCELLS STRUCTURES CAN DEVELOP WITHIN OR
AHEAD OF THE LINE.

It would not surprise me if SPC upgraded some of the region under the slight risk to moderate risk at a later time given the severe weather parameters coming together Friday into Friday night.

And, checking out some of those parameters;

As of 5pm Friday, the projected maps;

CAPE on the map (basically the energy or "dynamite" in the air that is projected available for these storms).
In meteorology, convective available potential energy (CAPE),[1] sometimes, simply, available potential energy (APE), is the amount of energy a parcel of air would have if lifted a certain distance vertically through the atmosphere. CAPE is effectively the positive buoyancy of an air parcel and is an indicator of atmospheric instability, which makes it very valuable in predicting severe weather.


Here we are destined for 2500-3000 J/kg (measured in joules per kilogram) at maximum heating, certainly sufficient enough when combined with the other factors below for severe weather.


Resulted Lifted Index (measure of the unstable air) at maximum heating on Friday along with the cold front axis;

The lifted index (LI) is the temperature difference between an air parcel lifted adiabatically Tp(p) and the temperature of the environment Te(p) at a given pressure height in the troposphere (lowest layer where most weather occurs) of the atmosphere, usually 500 hPa (mb). When the value is positive, the atmosphere (at the respective height) is stable and when the value is negative, the atmosphere is unstable.

     LI is generally scaled as follows:
  • LI 6 or Greater, Very Stable Conditions
  • LI Between 1 and 6 : Stable Conditions, Thunderstorms Not Likely
  • LI Between 0 and -2 : Slightly Unstable, Thunderstorms Possible, With Lifting Mechanism (i.e., cold front, daytime heating, ...)
  • LI Between -2 and -6 : Unstable, Thunderstorms Likely, Some Severe With Lifting Mechanism
  • LI Less Than -6: Very Unstable, Severe Thunderstorms Likely With Lifting Mechanism

 No question about the instability measured and available (ave of -7 > -9);


What about the shear available for the storms?

Bulk Shear

Bulk Shear - The bulk wind difference over a layer, calculated by vector subtraction. Bulk shear through 0-6 km AGL layer discriminates strongly between supercell and nonsupercell thunderstorm environments. The transition from nonsupercell to supercell thunderstorms occurs as the 0-6 km bulk wind difference increases from roughly 25 kt to 40 kt, with larger values favoring supercells. Research also suggests that increasing values in the 0-6km layer correlate with increasing tornado potential.

In the map below we look at the Bulk Shear from the surface to 500 MB (18,000 ft);

SFC-500MB Bulk Shear
Represents the boundary layer through 500MB above the ground, the shear vectors denote the change in wind throughout this height. Thunderstorms become more organized and long lived as vertical shear increases. Supercells are commonly associated with vertical shear values (Bulk shear values) of 35-40KT or better at this height.

While we have strong bulk shear in north and central Michigan, it is just beginning to nose into Southern Michigan - so it's CORE placement is a bit far north for Southeast Lower Michigan but in time, brushes the region. It will affect the storms developing to our northwest (most likely the squall line that is generated that will push through the region in the evening).



Upper Jet: (at 34,000 ft);
The most important feature to the meteorologist at the 250mb pressure level is the winds. The winds are important as its the typical location of the jet stream. The jet stream at 250 MB is located about 34,000 feet /33,000-35,000ft/. In this case, the right-rear quadrant of the wind core (which aides effectively in storm development) is a powerful jet core of 75-90 knots crossing northern and central Michigan late Friday afternoon and evening.



Finally;

Of course, this is all in projected model-land /GFS/ and has been, for a few days now and does bear watching for confirmation! If the atmosphere dynamics come together as projected, severe weather including a squall-line is likely!

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



7/16/13

NICE AND BRIGHT TO BLACK AS NIGHT; THE JULY 16TH, 1980, DERECHO

Step back in time on the 33rd 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!
 

NICE AND BRIGHT TO BLACK AS NIGHT!

THE JULY 16TH, 1980, DERECHO

Written by: William R. Deedler, Weather Historian
Originally written:
July 22nd, 2005 
 
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 

 

Surface map from 8 am EDT, July 16th, 1980; click on image to enlarge A low pressure area with attending warm and cold fronts (map-2) pushing through the Upper Midwest 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 (map-3) 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 (see storm report below) 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 CommunitiesDate
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. Asley, 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.

Graph of wind gusts by month for the U.S.; click on image to enlarge Note the graph to the right 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).






More on the Derecho by Dr. Fujita in 1981
http://www.spc.noaa.gov/misc/AbtDerechos/papers/Fujita_1981.pdf

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

7/11/13

Grand Daddy of all Heatwaves!

THE "GRAND DADDY" OF SOUTHEAST MICHIGAN HEAT WAVES 

 (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