Weather Extremes

Why was the Chicago Heat Wave of 2012 so much less deadly than that of 1995?

By: weatherhistorian, 6:22 PM GMT on July 27, 2012

Why was the Chicago Heat Wave of 2012 so much less deadly than that of 1995?

In July 1995 some 500-750 people died in Chicago during a torpid 5-day heat wave on July 12-16 that hit the city. This summer, similar temperatures occurred in Chicago on July 3-7 but there were relatively few heat-related fatalities associated with it. Why?

A steamy Chicago during the great July 1995 heat wave. An estimated 500-750 deaths have been attributed to the event. Photo by Gary Braasch, ‘Earth Under Fire’.

A Meteorological Comparison Between July 1995 and July 2012 in Chicago

Comparing the actual temperatures measured during each heat wave we can see that statistically the warmest five consecutive days were virtually the same. The table below shows the temperatures measured at Midway Airport. Midway is a much more relevant site than O’Hare Airport since it rests in South Chicago in the midst of, or close, to the very neighborhoods that most of the fatalities occurred in 1995.

A comparison of actual temperatures over the course of the five hottest days in July 1995 and July 2012 at Midway Airport on the south side of Chicago.

However, a key difference between the two heat waves was the humidity factor. The THI (Temperature-Humidity-Index) was considerably higher in 1995 and the periods of THI above key thresholds much longer. As NWS-Chicago put it in a recent statement on the subject:

“Meteorologically speaking, the most striking difference between the 2 heat waves was certainly the heat indices experienced during the afternoon hours. Generally speaking, heat indices between 95°F and 105°F can be tolerated with appropriate precautions, but when heat indices get over 105°F and particularly up to 115°F the ability of the body to keep its internal temperature regulated dramatically decreases”.

The charts below compare the average daytime heat indices between the 2 heat waves. This clearly shows that the 1995 heat wave was much more intense so far as THI was concerned during the daytime hours:

The maximum THI reached at any one time was 111° in 2012 and 119° in 1995 (the warmest THI on record for Chicago).

A comparison of THI indices over the course of the warmest four and a half days during the heat waves of 1995 and 2012. Graph from NWS-Chicago.

Non-Meteorological Factors Contributing to the Difference in Heat-related Fatalities

The American Journal of Public Health published an article in September 1997 (Vol. 87, No. 9, pp. 1515-1518) titled Mortality in Chicago Attributed to the July 1995 Heat Wave by Steven Whitman et al. One issue the authors put to rest was whether or not the criteria used by the Cook County medical examiners office to certify heat-related deaths were over estimated (Mayor Daley at the time claimed this was the case). Examination of the excess mortality data indicated that this was not the case. The article then focused on how weather played a roll in the excessive death rate. They reported that it was not just the temperature that contributed to the high mortality rates but rather a synoptic combination of temperature, cloud cover, wind speed, and, of course, humidity. But this was not the key problem.

Ultimately the report concluded that weather alone was insufficient to explain the excessive mortality rate (especially when compared to earlier extreme heat waves in Chicago). The real culprit was “a severe public health problem at the time of occurrence”, an oblique reference at the ineptitude of the response of the local government to the heat emergency.

A day-to-day comparison of the daily heat-related deaths to the actual temperature and heat THI index from July 10-20, 1995. Note how the death rate peaked following the actual peak of the highest temperatures. Death from heat does not happen suddenly but is rather a function of time (of consistent extreme heat). Graph from “Mortality in Chicago Attributed to the July 1995 Heat Wave’, American Journal of Public Health, Vol. 87, No. 9, p. 1516.

One thing that apparently has vastly improved in Chicago since 1995 is the local emergency response to extreme weather events (not just heat waves). There is a much improved heat watch/warning/advisory system in place now compared to 1995 thanks to the NWS and the city’s emergency response facilities. And finally of course, and of critical importance, many more inner city households have air-conditioning units at their disposal now than they did in 1995.


As we have seen in the past, Hurricane Katrina comes to mind, it is not necessarily just the weather that plays a roll in mass casualties during extreme weather events, but also non-meteorological factors as well.

Being prepared for ‘worst-case scenarios’, so far as the weather is concerned, seems to be a lesson that takes time to catch on. In the Chicago instance, at least, the lesson seems to have been learned.

REFERENCES: National Weather Service, Chicago ‘A Meteorological Comparison Between July 1995 and July 2012 Heat Wave’, July 23, 2012.

‘Mortality in Chicago Attributed to the July 1995 Heat Wave’, American Journal of Public Health, Vol. 87, No.9, September 1997 by Steven Whitman, PhD; Glen Good, MS; Edmund R. Donahue, MD; Nanette Benbow, MAS; Wenyan Shou, MS; and Shanxuan Mou, MS.

An excellent book about the Chicago 1995 heat wave is ‘Heat Wave: A Social Autopsy of Disaster in Chicago’ by Eric Klineberg.

KUDOS: Steve Gregory for bringing this to my attention.

Christopher C. Burt
Weather Historian

Temperature Heat

Updated: 6:29 PM GMT on July 27, 2012


New Continental Cold Record for Africa Discovered?

By: weatherhistorian, 7:28 PM GMT on July 20, 2012

New Continental Cold Record for Africa Discovered?

A possible new candidate for the coldest temperature ever measured on the continent of Africa may have been uncovered.

The Moroccan national meteorology directorate has recently completed scanning and digitizing of many of its old climate records and made them available for viewing by the public. Temperature detective Maximiliano Herrera has reviewed these documents and noticed that a site in the Atlas Mountains of Morocco named Oussikis apparently measured a low temperature of -24.1°C (-11.4°F) on February 11, 1935. This occurred on the same day as the currently recognized African continental absolute minimum temperature record of -24.0°C (-11.2°F) was observed at Ifrane, also in the Atlas Mountains.

The beautiful Atlas Mountain Range of Morocco extends for about 600 km (400 miles) on a NE-SW axis in the heart of the country. Its highest peak is Jbel Toubkal at 4165m (13,352’). Photographer unidentified.

Oussikis rests at an altitude of 2,100 meters (6,890 feet) and Ifrane at 1,635 meters (5,364 feet) so the higher altitude of Oussikis lends credibility to the potential new record. The two towns are about 200 km (125 miles) from one another, Oussikis being to the southwest of Ifrane.

A map of Morocco showing the relative locations of Ifrane and Oussikis. Google Earth.

Fatima Driouech of the Climate Services at the Direction de la Meteorologie National of Morocco has noted that whereas Ifrane is classified as a ‘meteorological station’ Oussikis is classified as a ‘climatological post’. I believe this distinction is similar to the difference between a first-order weather site versus a COOP site here in the U.S. In any case, Fatima is looking into the reliability of the Oussikis data.

The cold wave that enveloped Morocco in February 1935 was without equal. Another site in the mountains between Ifrane and Oussikis, Assif-Melloul located at 2,200 meters (7,218 feet), recorded a temperature of -23°C (-9.4°F) during this same event.

Here is a scanned cover of the 1935 Moroccan data book and the two pages relevant to Ifrane, Oussikis, and Assif-Melloul.

I will keep you posted concerning any new information the Moroccan authorities may uncover concerning this possibly significant discovery.

In the meantime, the WMO review of Africa’s (and the world’s) hottest temperature of 58°C (136.4°F) at Azizia, Libya on September 13, 1922 is nearing its conclusion. Results should be released sometime in the next month or so.

Christopher C. Burt
Weather Historian

KUDOS: To ace temperature researcher Maximiliano Herrera

Temperature cold


June 2012 Global Weather Extremes Summary

By: weatherhistorian, 5:40 PM GMT on July 07, 2012

June 2012 Global Weather Extremes Summary

June featured many notable extreme weather events from around the world. Extreme heat in the U.S. from Colorado to the East Coast, record-breaking rainstorms and floods in Duluth, Minnesota and Pensacola, Florida, and a powerful derecho event that caused extensive damage and fatalities from Illinois to Virginia. Britain suffered its wettest and cloudiness June on record. Typhoons and drought plagued portions of East Asia, and massive monsoon floods wreaked havoc in India and Bangladesh.

Below is a summary some of the month’s highlights.


The most notable event of the month was the extraordinary heat wave (and wild fires) that enveloped the U.S. from Colorado to the East Coast. Details about this event may be read in my previous two blogs. The fires in Colorado near Colorado Springs and Fort Collins were the worst in the state’s history, destroying over 600 homes and killing three. On June 29th one of the most powerful derechos on record swept across the country from Illinois to Virginia killing 26, leaving up to 3.5 million without power and causing hundreds of millions of dollars in damage.

Taken aboard the International Space Station about 240 miles above earth, this NASA photo shows the large Fonteniel Fire burning in west-central Wyoming on June 30th. NASA image credit.

Maine received over 8” of rain in some places (8.42” at Bridgeton) on June 3-4 as a low-pressure system skirted the Atlantic Coast. Training thunderstorms deluged Duluth, Minnesota with 7.24” of rain, 6.90” of which fell in just 24 hours on June 19-20, an all-time record amount (previous record was 5.79” on Aug. 22-23, 1978). Pensacola, Florida was deluged with 15.05” on June 9-10 when a sub-tropical wave of moisture moved inland from the Gulf of Mexico. West Pensacola reported an astonishing 21.70” in a 24-hour period.

A car fell into a huge sink hole on Skyline Parkway in Duluth following the record 7.24” of rain that fell on June 19-20. Photo by Bob King/Duluth News.

Later in the month Tropical Storm Debby crossed over northern Florida from the Gulf of Mexico to the Atlantic deluging some areas around Tallahassee with flooding rains.

A powerful late-season cold front moved through Nevada on June 6th dropping the temperature from a record high of 90° on June 3rd to a record low of 24° on June 5th at Eureka, Nevada. For the first time known in June measureable snow was reported at Winnemucca (just 0.1”) and Elko (0.5”) on June 6th.

Unusual late spring heat baked the shores of Hudson Bay in Canada on June 10-11 when temperatures reached 35°C (95°F) at Moosonee, Ontario and Waskaganish, Quebec. In Quebec this was close to the hottest temperature on record for the site.

The coldest temperature measured in the northern hemisphere during June was -29.9°C (-21.8°F) at Summit, Greenland.


After a year of drought, Chile finally received some substantial rainfall in mid-June. Santiago recorded about 35mm of rainfall (1.5”). In 2011 it recorded only a total 110 mm (4.32”) of rainfall (30% of normal). The June rainstorm, however, led to mudslides in the mountains causing damage at Farellones, a ski resort in central Chile.

A record June temperature for Brazil was reached at Oeras, Piau State on June 22nd when 38.7°C (101.2°F) was recorded. This was also the warmest temperature measured in the southern hemisphere during the month of June.


The U.K. suffered through its wettest June since at least 1910 and coolest such since 1991. The miserable weather did little, however, to dampen the enthusiastic Diamond Jubilee celebrations for the Queen.

A departure from average precipitation map for the U.K. for this past June, the wettest June in modern U.K. records. Map from U.K. Met Office.

Flooding rains occurred in Wales and other sections of the Isles with 93.8mm (3.69”) in Blencathra, Cumbria being the greatest 24-hour total on June 22-23. The coldest temperature during the month was -3.5°C (25.7°F) at Loch Glascamoch in Scotland on June 5th and the warmest 28.6°C (83.5°F) at Gravesend, Kent on June 28th.

Very warm weather affected the Iberian Peninsula, Italy, and other European locations during the month. Sonnblick, Austria (a mountain top weather station situated at 3100m (about 10,200’) measured its warmest temperature on record (going back to 1886) when 15.3°C (59.5°F) was measured on June 30th.


Landslides in the eastern Ugandan district of Bududa (caused by torrential rains) killed an undetermined number of people on June 25th. Some reports claimed hundreds had perished with at least 30 confirmed fatalities.

A temperature of 1.6°C (34.9°F) was recorded at Karoi, Zimbabwe on June 12th, an all-time cold record for the site.


A heat wave in the Middle East during the first week of June resulted in the all-time heat record for Mecca, Saudi Arabia, being broken on June 2nd when the temperature hit 51.4°C (124.5°F). This was also the hottest temperature measured in the world during the month. Blistering heat also affected Iraq (50.5°C/122.9°F at Fao) and Kuwait (50.9°C/123.6°F at Mitribah).

A couple of locations in India also broke their all-time heat records: 47.3°C (117.3°F) at Kakinada and 46.7°C (116.1°F) at Bhubaneswar during June.

The monsoon season has been especially devastating so far along the banks of the Brahmaputra River in northeast India and Bangladesh. Over 2000 villages have been flooded and at least 190 deaths reported so far. Almost 20 million people in all have been displaced.

A villager makes his way through floodwaters in Kaziranga National Park in northeastern India. Some 20 million have been displaced by the floods so far. Photo by Biju Boro, AFP.

Flash floods also struck northern Afghanistan killing 37 and southern China between June 20-30 resulting in the deaths of 50-100.

Typhoon Guchol, at one point packing 140 mph winds, struck the Japanese Island of Honshu between Osaka and Tokyo on June 19th. Fortunately, the storm weakened to minimum typhoon strength before making landfall. Rainfall amounts up to 500mm/20” were reported from some mountainous locations.

Further north, the Korean Peninsula continued to endure its worst drought in at least 105 years. In poverty-stricken North Korea two-thirds of the 24 million population are facing chronic food shortages.


It was the 12th coolest June on record nationally for Australia with one all-time record minimum temperature being observed with a -3.0°C (26.6°F) at Urandangi on June 30th. The coldest temperature for the month anywhere in Australia was -11.0°C (12.2°F) at Charlotte Pass, New South Wales on June 8th and the warmest 36.0°C (96.8°F) at Timber Creek, Northern Territory on June 15th. The greatest calendar precipitation was 203.4mm (8.01”) at Reeves Knob, Victoria on June 5th.

Maps showing the rainfall decile departures (top) and minimum temperature decile departures (bottom) for Australia during June.Maps from the Australian Bureau of Meteorology.


New Zealand was unusually cold during the month with a record cold maximum of just 0.4°C (32.7°F) being set at Christchurch on June 6th (records go back to 1863 there). Snow fell down to sea level on the western coast of the South Island, a very rare occurrence. The coldest temperature reported in the country during the month was -11.8°C (10.8°F) at Darfield on June 7th. The warmest was 22.0° (71.6°F) at Wairoa on June 6th (quite a contrast just a day apart!). The heaviest calendar day rainfall was 151mm (5.94”) at Greymouth on June 5th.


The coldest temperature in the southern hemisphere and the world during June was -81.4°C (-114.5°F) recorded at Vostok on June 11th.

KUDOS Thanks to Maximiliano Herrera for global temperature extremes data, Stephen Burt for the U.K. extremes, and Jeremy Budd for New Zealand weather extremes.

I will be away from my office until July 18th and will post my next blog on July 20th.

Christopher C. Burt
Weather Historian


The Amazing June Heat Wave of 2012: Part 2 June 28-30. UPDATE: 113° Smyrna, TN

By: weatherhistorian, 11:15 PM GMT on July 01, 2012

The Amazing June Heat Wave of 2012 Part 2: The Midwest and Southeast June 28-30

After scorching portions of the West and Plains early last week, the amazing heat wave of June 2012 slid eastward on Thursday, June 28, continuing to astonish us with more all-time heat records. Below is a summary of those.

Set Up for the Heat Wave in the East

The powerful upper level high ridge slid out of the Plains and anchored itself over Tennessee by Friday. Compare the 500 mb charts that I posted in my blog on Friday with those below.

500 mb chart for 7 a.m. on June 27th. Map from Daily Weather Maps, NOAA.

500 mb chart for 7 a.m. on June 30th. Note that another dome of high pressure is developing in the southwest again. Map from Daily Weather Maps, NOAA.

All-time Heat Records Broken or Tied June 28-30

There is no point in listing or even attempting to summarize all of the June monthly records set in the region from Missouri to Maryland and south to Georgia during the June 28-30 period. The 108° in St. Louis on June 28th was perhaps the most significant of those. What was truly astonishing was the number of all-time any month records that were broken or tied.

This is especially extraordinary since they have occurred in June rather than July or August when 95% of the previous all-time heat records have been set for this part of the country (unlike the Southwest where June is often the month that all-time heat extremes are recorded).

Maximum and minimum temperatures recorded across the U.S. on June 29th. Map from Daily Weather Maps, NOAA.


109° at Cairo Airport on June 29th broke the all-time record for Cairo (old record 106° on August 9,1930) and also surpasses Illinois’ June state record of 108° at Palestine in June 1954. Chicago reached 100° at both O’Hare and Midway Airports on June 28th, the first 100° reading for either site since 2005. As of July 1st Chicago O’Hare has experienced 18 90°+ days so far this year, the most on record at this point in the season and about what the average number of such days is for an entire year.


106° was measured at Fort Wayne, Indiana on June 28 (tying the all-time record set on 7/14/1936).


Paducah recorded 108° on June 29th, an all-time official record (although a previous site in Paducah measured 112° in July 1930). Bowling Green hit 109° on June 29th, short by 1° of Kentucky’s all-time state June record of 110° at St. John’s Academy in June 1936. All-time heat records were broken at Jackson (104°) and London (105°), but these sites have short periods of record.


This has been the most intense heat event in Tennessee state history (at least for the eastern two-thirds of the state). All-time records were achieved at the following sites that have significant POR’s (periods of record):

109° Nashville on June 29th (old record 107° on 7/28/1952)

107° Chattanooga on June 30th and July 1st (old record 106° on 6/29/2012 and 7/28/1952)

105° Knoxville on June 30th and July 1st (old record 104° on 7/12/1930)

103° Bristol on June 30th (old record 102° 7/28/1952)

A reading of 113° was reported from Smyrna on June 29th. If verified this would tie the all-time state record for any month: Perryville’s 113° in July and August of 1930. UPDATE: NWS has informed me that the Smyrna site is consistently too hot on sunny days. Hottest temp for TN officially is 110° at Woodbury, still a state monthly record for June.


Again, this was one of the hottest events in Georgia state history. The following all-time (any month) records were tied or broken:

109° Athens on June 29th (old record 108° on 7/12/1930)

108° Macon on June 30th (ties same on 7/17/1980)

106° Atlanta on June 30th (old record 105° on 7/17/1980)

106° Columbus on June 30th (ties same on 9/5/1925)

The Athens’ reading of 109° was just 1° short of the June state record of 110° set at Warrenton in June 1959. Perhaps some late COOP reports will upset that figure. A reading of 107° was recorded at the Rome WSO Airport site on June 30th, an all-time record (old record 106° on 7/29/1952) for that location (POR 1948-2012). However, the original Rome weather station, with a POR from 1893-2010, reached 109° on July 20, 1913.


This was almost certainly the most intense heat wave in South Carolina’s history. Here’s the run down (all-time any month heat records):

109° Columbia on June 29th and 30th (old record 107° on multiple occasions).

107° Greenville on July 1st (old record 105° set on 6/29/2012 and 8/10/2007, although 106° was recorded by the Army Signal Corps on July, 18, 1887).

Temperatures of 113° were reported from Johnston and the University of South Carolina site in Columbia on June 29th. If verified these would establish a new all-time state heat record for any month at any location (current record being 111° at Camden on June 28, 1954).


All-time heat records tied or broken:

105° Raleigh on June 29th and 30th (ties previous record set on 8/21/2007 and 8/18/1988)

104° Charlotte on June 29th and 30th (ties same on 8/9/2007, 8/10/2007, and 9/6/1954).

Southern Pines reported a temperature of 108° on June 30th. If verified this would be a new June state heat record beating the 107° reported from Lake Mitchie in June 1959 but short 2° of a suspicious reading of 110° at Fayetteville on August 21, 1983. There appears to be no data to support the figure from Fayetteville in 1983. The hottest indisputable record for North Carolina is 109° at Weldon on September 7, 1954.


The 104° at National Airport in D.C. on June 29th fell 2° short of the D.C. all-time record of 106° set on July 20, 1930. You may have noticed that 1930 pops up often in terms of all-time heat records in the Southeast.

108° was reported from Petersburg on June 29th. If verified this would be the all-time Virginia state heat record for the month of June (current record being 107° at Lincoln in June 1934). The all-time ‘any month’ record for Virginia is disputed: 110° from Balcony Falls on July 15, 1954 appears suspicious and the Virginia State Climate Office has disallowed it. The next candidate is 109° at Lincoln on July 10, 1936. 109° was also reported at the Williamsburg Airport on July 25, 2010, but this appears to be an unofficial reading.

Surface temperatures at 4 p.m. on July 1st, the last day of the record-breaking portion of the heat wave. The white shaded areas represent temperatures of 105°+. Image from UCAR.


There is no imminent conclusion to this heat wave. As the high-pressure ridge over the Southeast weakens, a new ridge is developing again over the Southwest and threatens to form a broad flat upper-level dome stretching from New Mexico to Georgia. An up-to-date list of all the ‘all-time’ heat records broken at significant sites since June 23 may be found on ‘Wunderground U.S. Records’ under the ‘Climate’ tab at the top of the WU front page (scroll down to ‘Record Extremes’.)

18 of the 298 locations I follow closely (because of their long POR’s and representation of U.S. climate) have already broken or tied their all-time heat records.

It is just July the 1st and the summer has just begun.

Christopher C. Burt
Weather Historian

Heat Temperature

Updated: 1:50 AM GMT on July 03, 2012


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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Weather Extremes

About weatherhistorian

Christopher C. Burt is the author of 'Extreme Weather; A Guide and Record Book'. He studied meteorology at the Univ. of Wisconsin-Madison.