Chicago placed under first excessive heat warning since 2006
By Tom Skilling
It's been four years since Chicago has been placed under an "excessive heat warning" by the National Weather Service. The current warning runs through 7 p.m. Friday as do the heat advisories which have been hoisted over the remainder of the Chicago area.
Guidelines for the issuance of such advisories were developed in the wake of the city's deadly July 1995 heat wave. To this day -- 15 years later -- the event, which claimed more than 700 lives, remains Chicago's single worst natural disaster. In that hot spell, temperatures soared to 106 degrees at Midway Airport which, in tandem with stifling atmospheric moisture levels that included dew points of 82 degrees, led to a never-before-seen 125-degree heat index here.
The elderly and those with pre-existing medical conditions aggravated by the onset of heat comprised the majority of the deadly heat wave's victims. But the extent of death at the time took area residents and officials by surprise and led to a major effort to more clearly understand the combination of atmospheric conditions which were capable of generating such human carnage.
The current hot spell, which is expected to ease late this weekend and early next week, isn't anywhere near as extreme. Neither temperatures nor humidities will come close to 1995's off-the-charts levels. But the low to mid 90s predicted Thursday and Friday coupled with oppressive afternoon dew points at or above 75 degrees will lead to a 98 to 107-degree peak heat indices.
It's been four years since Chicago has been placed under an "excessive heat warning" by the National Weather Service. The current warning runs through 7 p.m. Friday as do the heat advisories which have been hoisted over the remainder of the Chicago area.
Guidelines for the issuance of such advisories were developed in the wake of the city's deadly July 1995 heat wave. To this day -- 15 years later -- the event, which claimed more than 700 lives, remains Chicago's single worst natural disaster. In that hot spell, temperatures soared to 106 degrees at Midway Airport which, in tandem with stifling atmospheric moisture levels that included dew points of 82 degrees, led to a never-before-seen 125-degree heat index here.
The elderly and those with pre-existing medical conditions aggravated by the onset of heat comprised the majority of the deadly heat wave's victims. But the extent of death at the time took area residents and officials by surprise and led to a major effort to more clearly understand the combination of atmospheric conditions which were capable of generating such human carnage.
The current hot spell, which is expected to ease late this weekend and early next week, isn't anywhere near as extreme. Neither temperatures nor humidities will come close to 1995's off-the-charts levels. But the low to mid 90s predicted Thursday and Friday coupled with oppressive afternoon dew points at or above 75 degrees will lead to a 98 to 107-degree peak heat indices.
Excessive heat warnings are issued when any of the following three conditions are predicted: three consecutive days of heat indices 100 to 105 degrees; two consecutive days with heat indices 105 to 110, or a single day in which the critical index tops 110-degrees.
Deaths from heat top those which occur in all other weather extremes
Far from being just a nuisance, heat is the most deadly of all extreme weather events. The number who perish annually across the U.S. as a result of extreme heat exceeds those killed by tornadoes, flash floods, hurricanes, lightning or cold weather.
There are now estimates that as many as 15,000 may have already died in Russia in the record heat wave which is predicted to continue there for the foreseeable future after a brief break Wednesday. And the final tally could end up even worse. Summer temperatures have reached 100 degrees at Moscow weather stations in the past several months, the first time in 130 years of weather records there that triple-digit reading have occurred.
Temperatures in Moscow for the meteorological summer season which began June 1 have topped 90 degrees on 31 days and have reached or exceeded 100 degrees five days -- a stunning development in a city with "normal" summer highs in the low to mid 70s. The summer season there has averaged a remarkable 9.6 degrees above normal. All are stats which place the modest nature of Chicago's latest flirtation with heat and humidity in perspective.
Heat Thursday extends 80-degree streak to 42 days -- the most here in 55 years
Wednesday's 90-degree high at O'Hare became the official site's 16th day at or above 90 degrees while Midway's 91-degree reading marked the South Side site's 18th such day. Not even the day's lake breeze was able to spare the city's lakefront from a rendezvous with heat. Northerly Island topped out at 93.
Fewer thunderstorms than in many recent weeks here are to provide a backdrop for the hot temperatures predicted Thursday and Friday. Thermometer readings are predicted to top out at 94 Thursday and 95 Friday. Each reading would tie or exceed 2010's highest temperature to date: 94 degrees at O'Hare and 95 degrees at Midway and the lakefront recorded back on July 23. It also assures the city's record for consecutive 80 degree or higher temperatures based on over 140 years of official weather records will occur Thursday and that a new record will be established Friday.
St. Louis really hot; a 50th day over 90 due Thursday
As hot as Chicago's weather will be the next few days, residents of St. Louis -- where the temperature hit 100 degrees Wednesday and the heat index topped out at 112 degrees -- are to mark 2010's 50th day at or above 90 degrees Thursday. There could be another 100-degree reading today.
Seventeen states remain under heat advisories or excessive heat warnings the remainder of the work week.
Huge pattern change has an early autumnal look next week
Big changes in North America's weather pattern loom. The dome of warm air so frequently a part of the meteorological scene over Greenland and the northwest Atlantic in recent years -- the feature referenced so often here as the "Greenland Block" -- gets back in business in the coming week. It's predicted by computer models that it will produce strong ridging over the western Atlantic, which induces strong troughing aloft over central North America. The northwest steering winds that will run from Canada into the nation's heartland will arrive late this weekend and into next week. They have an early autumn look and promise to drop temperatures and humidities here.
But it's unlikely we've seen the last of this year's hot weather. Warming is predicted again the following weekend.
Approximately 400 people die each year from exposure to heat, according to the Centers for Disease Control and Prevention. Our bodies dissipate heat by varying the rate and depth of blood circulation, by losing water through the skin and sweat glands, and as a last resort, by panting, when blood is heated above 98.6 degrees Fahrenheit.
Sweating cools the body through evaporation. However, high relative humidity retards evaporation, robbing the body of its ability to cool itself. When heat gain exceeds the level the body can remove, body temperature begins to rise, and heat-related illnesses and disorders may develop.
If you must be out in the heat:
A heat advisory or warning has been issued. Now what do you do? Before Exposure
Extreme heat is more than an issue of discomfort. It forces the body into overdrive as it tries to stay cool through perspiration and evaporation.
Because heat-related deaths are preventable, people need to be aware of who is at greatest risk and what actions can be taken to prevent a heat-related illness or death.
The elderly, the very young, and people with mental illness and chronic diseases are at highest risk. However, even young and healthy individuals can succumb to heat if they participate in strenuous physical activities during hot weather.
People in urban areas are at high risk, too, because the stagnant atmospheric conditions trap pollutants in the air, which, when breathed can trigger respiratory problems for many people.
Other conditions related to risk include age, obesity, fever, dehydration, heart disease, mental illness, poor circulation, sunburn, and prescription drug and alcohol use.
The effects of extreme heat can undermine physical well-being so slowly and subtly that the dangers aren't apparent until it's too late.
In regions of low humidity, the most common human response to extreme heat is dehydration. Exposed to direct sunlight and temperatures in excess of 90 degrees Fahrenheit, a human can lose as much as half a gallon of water every 10 minutes, and this dehydration can seriously interfere with one's internal thermostat.
Heat-Related Illnesses
No matter where you live, it is important to recognize the real dangers of extreme heat and take action to offset its impact at its earliest stages.
The gradual nature of extreme heat's effects on the body makes it important to be aware of heat-related illnesses:
Severe Sunburn
- So much more than a dermatologic issue, sunburn reduces the skin's ability to release excess heat, making the body more susceptible to heat-related illness.
Heat Cramps
- Muscle pains and spasms caused by heavy exertion, which triggers heavy perspiration. These usually involve the muscles of the abdomen or legs.
Heat Exhaustion
- A mild form of shock marked by heavy sweating, weakness, cold, clammy skin, a weak pulse, fainting and vomiting. This usually occurs when people have been exercising heavily or working in a warm humid place. Blood flow to the skin increases -- in an attempt to cool the body -- causing blood flow to vital organs to decrease.
If not treated, a victim's condition can worsen; the body temperature can keep rising, possibly leading to heat stroke.
Heat Stroke
- A truly life-threatening condition in which the body's internal thermostat has ceased to work. The ability to sweat stops, and the body's temperature can rise so high that brain damage and death may occur in 10-15 minutes unless medical help is immediate.
How Will You Be Warned?
If you are in the peak summer months, and the temperature and/or humidity has been unusually high for several days, anticipate an extreme heat emergency situation.
Keep an eye on The Weather Channel and weather.com to track the heat index and to get information about excessive heat potential.
Although threshold criteria may vary depending on the location, two kinds of alerts are generally issued.
Heat Advisory
- Issued when the heat, or combination of heat and humidity, is expected to become an inconvenience for much of the population, and a problem for some.
Excessive Heat Warning
- Issued when the heat, or combination of heat and humidity, is expected to be dangerous for a large portion of the population.
[Source: CDC]
Deaths from heat top those which occur in all other weather extremes
Far from being just a nuisance, heat is the most deadly of all extreme weather events. The number who perish annually across the U.S. as a result of extreme heat exceeds those killed by tornadoes, flash floods, hurricanes, lightning or cold weather.
There are now estimates that as many as 15,000 may have already died in Russia in the record heat wave which is predicted to continue there for the foreseeable future after a brief break Wednesday. And the final tally could end up even worse. Summer temperatures have reached 100 degrees at Moscow weather stations in the past several months, the first time in 130 years of weather records there that triple-digit reading have occurred.
Temperatures in Moscow for the meteorological summer season which began June 1 have topped 90 degrees on 31 days and have reached or exceeded 100 degrees five days -- a stunning development in a city with "normal" summer highs in the low to mid 70s. The summer season there has averaged a remarkable 9.6 degrees above normal. All are stats which place the modest nature of Chicago's latest flirtation with heat and humidity in perspective.
Heat Thursday extends 80-degree streak to 42 days -- the most here in 55 years
Wednesday's 90-degree high at O'Hare became the official site's 16th day at or above 90 degrees while Midway's 91-degree reading marked the South Side site's 18th such day. Not even the day's lake breeze was able to spare the city's lakefront from a rendezvous with heat. Northerly Island topped out at 93.
Fewer thunderstorms than in many recent weeks here are to provide a backdrop for the hot temperatures predicted Thursday and Friday. Thermometer readings are predicted to top out at 94 Thursday and 95 Friday. Each reading would tie or exceed 2010's highest temperature to date: 94 degrees at O'Hare and 95 degrees at Midway and the lakefront recorded back on July 23. It also assures the city's record for consecutive 80 degree or higher temperatures based on over 140 years of official weather records will occur Thursday and that a new record will be established Friday.
St. Louis really hot; a 50th day over 90 due Thursday
As hot as Chicago's weather will be the next few days, residents of St. Louis -- where the temperature hit 100 degrees Wednesday and the heat index topped out at 112 degrees -- are to mark 2010's 50th day at or above 90 degrees Thursday. There could be another 100-degree reading today.
Seventeen states remain under heat advisories or excessive heat warnings the remainder of the work week.
Huge pattern change has an early autumnal look next week
Big changes in North America's weather pattern loom. The dome of warm air so frequently a part of the meteorological scene over Greenland and the northwest Atlantic in recent years -- the feature referenced so often here as the "Greenland Block" -- gets back in business in the coming week. It's predicted by computer models that it will produce strong ridging over the western Atlantic, which induces strong troughing aloft over central North America. The northwest steering winds that will run from Canada into the nation's heartland will arrive late this weekend and into next week. They have an early autumn look and promise to drop temperatures and humidities here.
But it's unlikely we've seen the last of this year's hot weather. Warming is predicted again the following weekend.
Heat Index Chart
| The Heat Index is the temperature the body feels when heat and humidity are combined. The chart below shows the Heat Index that corresponds to the actual air temperature and relative humidity. This chart is based upon shady, light wind conditions. Exposure to direct sunlight can increase the Heat Index by up to 15 degrees Fahrenheit. |
| Relative Humidity (%) | ||||||||||||||
| 40 | 45 | 50 | 55 | 60 | 65 | 70 | 75 | 80 | 85 | 90 | 95 | 100 | ||
 | 110 | 136 | - | - | - | - | - | - | - | - | - | - | - | - |
| 108 | 130 | 137 | - | - | - | - | - | - | - | - | - | - | - | |
| 106 | 124 | 130 | 137 | - | - | - | - | - | - | - | - | - | - | |
| 104 | 119 | 124 | 131 | 137 | - | - | - | - | - | - | - | - | - | |
| 102 | 114 | 119 | 124 | 130 | 137 | - | - | - | - | - | - | - | - | |
| 100 | 109 | 114 | 118 | 124 | 129 | 136 | - | - | - | - | - | - | - | |
| 98 | 105 | 109 | 113 | 117 | 123 | 128 | 134 | - | - | - | - | - | - | |
| 96 | 101 | 104 | 108 | 112 | 116 | 121 | 126 | 132 | - | - | - | - | - | |
| 94 | 97 | 100 | 102 | 106 | 110 | 114 | 119 | 124 | 129 | 135 | - | - | - | |
| 92 | 94 | 96 | 99 | 101 | 105 | 108 | 112 | 116 | 121 | 126 | 131 | - | - | |
| 90 | 91 | 93 | 95 | 97 | 100 | 103 | 106 | 109 | 113 | 117 | 122 | 127 | 132 | |
| 88 | 88 | 89 | 91 | 93 | 95 | 98 | 100 | 103 | 106 | 110 | 113 | 117 | 121 | |
| 86 | 85 | 87 | 88 | 89 | 91 | 93 | 95 | 97 | 100 | 102 | 105 | 108 | 112 | |
| 84 | 83 | 84 | 85 | 86 | 88 | 89 | 90 | 92 | 94 | 96 | 98 | 100 | 103 | |
| 82 | 81 | 82 | 83 | 84 | 84 | 85 | 86 | 88 | 89 | 90 | 91 | 93 | 95 | |
| 80 | 80 | 80 | 81 | 81 | 82 | 82 | 83 | 84 | 84 | 85 | 86 | 86 | 87 | |
| With Prolonged Exposure and/or Physical Activity: | |||
| Caution: Fatigue possible | Extreme Caution: Sunstroke, muscle cramps, and/or heat exhaustion possible | Danger: Sunstroke, muscle cramps, and/or heat exhaustion likely | Extreme Danger: Heat Stroke or Sunstroke likely |
Sweating cools the body through evaporation. However, high relative humidity retards evaporation, robbing the body of its ability to cool itself. When heat gain exceeds the level the body can remove, body temperature begins to rise, and heat-related illnesses and disorders may develop.
If you must be out in the heat:
- Limit your outdoor activity to morning and evening hours.
- Cut down on exercise. If you must exercise, drink two to four glasses of cool, nonalcoholic fluids each hour. A sports beverage can replace the salt and minerals you lose in sweat.
Warning: If you are on a low-salt diet, talk with your doctor before drinking a sports beverage.
- Try to rest often in shady areas.
- Protect yourself from the sun by wearing a wide-brimmed hat (also keeps you cooler) and sunglasses and by putting on sunscreen of SPF 15 or higher (the most effective products say "broad spectrum" or "UVA/UVB protection" on their labels).
Safety During a Heat Wave
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
A heat advisory or warning has been issued. Now what do you do? Before Exposure
Risk of Heat Cramps, Exhaustion, and Heat Stroke
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Because heat-related deaths are preventable, people need to be aware of who is at greatest risk and what actions can be taken to prevent a heat-related illness or death.
The elderly, the very young, and people with mental illness and chronic diseases are at highest risk. However, even young and healthy individuals can succumb to heat if they participate in strenuous physical activities during hot weather.
People in urban areas are at high risk, too, because the stagnant atmospheric conditions trap pollutants in the air, which, when breathed can trigger respiratory problems for many people.
Other conditions related to risk include age, obesity, fever, dehydration, heart disease, mental illness, poor circulation, sunburn, and prescription drug and alcohol use.
The effects of extreme heat can undermine physical well-being so slowly and subtly that the dangers aren't apparent until it's too late.
In regions of low humidity, the most common human response to extreme heat is dehydration. Exposed to direct sunlight and temperatures in excess of 90 degrees Fahrenheit, a human can lose as much as half a gallon of water every 10 minutes, and this dehydration can seriously interfere with one's internal thermostat.
Heat-Related Illnesses
No matter where you live, it is important to recognize the real dangers of extreme heat and take action to offset its impact at its earliest stages.
The gradual nature of extreme heat's effects on the body makes it important to be aware of heat-related illnesses:
- So much more than a dermatologic issue, sunburn reduces the skin's ability to release excess heat, making the body more susceptible to heat-related illness.
- Muscle pains and spasms caused by heavy exertion, which triggers heavy perspiration. These usually involve the muscles of the abdomen or legs.
- A mild form of shock marked by heavy sweating, weakness, cold, clammy skin, a weak pulse, fainting and vomiting. This usually occurs when people have been exercising heavily or working in a warm humid place. Blood flow to the skin increases -- in an attempt to cool the body -- causing blood flow to vital organs to decrease.
If not treated, a victim's condition can worsen; the body temperature can keep rising, possibly leading to heat stroke.
- A truly life-threatening condition in which the body's internal thermostat has ceased to work. The ability to sweat stops, and the body's temperature can rise so high that brain damage and death may occur in 10-15 minutes unless medical help is immediate.
If you are in the peak summer months, and the temperature and/or humidity has been unusually high for several days, anticipate an extreme heat emergency situation.
Keep an eye on The Weather Channel and weather.com to track the heat index and to get information about excessive heat potential.
Although threshold criteria may vary depending on the location, two kinds of alerts are generally issued.
- Issued when the heat, or combination of heat and humidity, is expected to become an inconvenience for much of the population, and a problem for some.
- Issued when the heat, or combination of heat and humidity, is expected to be dangerous for a large portion of the population.
[Source: CDC]
