National Weather Service United States Department of Commerce

Missouri Summer Weather Safety Week

Excessive Heat and Lightning

June 18 - 24, 2018

The National Weather Service (NWS), the Missouri Department of Health and Senior Services (DHSS) , and the State Emergency Management Agency (SEMA) have joined together to promote Missouri Summer Weather Safety Week 2017: Excessive Heat and Lightning. The following is important safety information that can save peoples lives. Please help spread the word about excessive heat and lightning safety so everyone can have a safe summer.

NWS Summer Weather Safety Web Site

1. Summary     pdf version
2. NWS Excessive Heat Web Site 
3. The Science of Lightning    pdf version
4. Lightning Safety     pdf version
5. Excessive Heat      pdf version
6. Who is Vulnerable to Heat?    pdf version
7. Heat Index     pdf version

8. Heat Advisory/Warning Criteria
9. Common Heat Disorders     pdf version
10.Heat Safety     pdf version

Children and Pets left in Vehicles! A Deadly Combination 

Click to Learn More.

Visit these other sites on the Internet for additional information

National Weather Service Heat Safety

National Weather Service Lightning Safety

Missouri State Emergency Management Agency

Missouri Department of Health and Senior Services (DHSS)
DHSS Hyperthermia

DHSS data and statistics on hyperthermia in Missouri

Center for Disease Control and Prevention

Two of the biggest weather hazards that affect the United States typically occur during the summer months: Lightning and Excessive Heat. The following chart shows the fatalities for 2016, along with 10 and 30 year averages. You can see that excessive heat deaths is the 30-year average leader, just ahead of flood deaths. 

United States Average Deaths

The U.S. Natural Hazard Statistics provide statistical information on fatalities, injuries and damages caused by weather related hazards. These statistics are compiled by the Office of Services and the National Climatic Data Center from information contained in Storm Data, a report comprising data from NWS forecast offices in the 50 states, Puerto Rico, Guam and the Virgin Islands.

Missouri Heat Related Deaths*

Year 2016 2015 2014 2013 2012 2011 2010 2009 2008 2007 2006
Deaths 25 17 12 15 52  53 27 14  10 39 27

Missouri Heat Related Deaths: 1980 - 2016: 1272

Note: DHSS has recently gone through a review of all past cases of heat related deaths and have made some changes to the numbers. Thus, some of these numbers are different than what was reported last year. 


Missouri Lightning Deaths
Year 2016 2015 2014 2013 2012 2011 2010 2009 2008 2007 2006
Deaths 0 2 1 1 0 3  1  2 1 2 0

The 3 Deaths in Missouri in 2011 tied with Utah for most in the United States in 2011

The above covers reports received by the National Weather Service in Missouri. Historically, deaths and injuries from lightning have been very under reported.

United States Lightning Deaths: 2016

United States Lightning Deaths: Thus far in 2017

United States Lightning Deaths: 2007 - 2017


Lightning Overview
At any given moment, there are 1,800 thunderstorms in progress somewhere on Earth. This amounts to 16 million storms a year! In the United States, there are an estimated 25 million cloud-to-ground lightning flashes each year. While lightning can be fascinating to watch, it is also extremely dangerous.
Underrated Problem

According to statistics kept by the National Weather Service, the 30 year average for lightning fatalities across the country is 61.  Lightning usually claims only one or two victims at a time, and because lightning does not cause mass destruction, such as from a tornado event or a hurricane, lightning generally receives much less attention than the more destructive storm-related events. Due to under reporting, it is estimated that, more realistically, about 100 - 120 deaths per year occur because of lightning. Documented lightning injuries in the United States average 300 per year; however undocumented lightning injuries are likely much higher. 


In Missouri there have been 97 deaths attributed to lightning from 1959 - 2012, an average of 2 deaths per year. In comparison, the the average number of deaths caused by tornadoes since 1950 has risen to 6. So overall, we are doing better in terms of lightning safety. 



The Science of Lightning
Lighting has been seen in volcanic eruptions, extremely intense forest fires, surface nuclear detonations, heavy snowstorms, and in large hurricanes. However it is most often seen in individual thunderstorms. We know the cloud conditions necessary to produce lightning, but cannot forecast the location or time of the next stroke of lightning from a storm.

Ice is Critical to the Lightning Process
The formation of ice in a cloud appears to be a very important element in the development of lightning in a storm. The collision of ice and water particles causes separation of the positive and negative electric charges in the particles. Positive charged ice particles tend to collect in the upper parts of the storm, with negative charged particles in the middle and lower parts of the storm. These opposite charges attract, thus "in-cloud" lightning is often produced.
Lightning to the Ground

As the negative particles gather at the bottom of the storm cloud, a pool of positively charged particles gather along the ground and travel with the storm. As the differences in charges increase, positively charged particles rise up taller objects such as trees, houses, and even people. If you are near a storm, and your hair stands on end, the particles are moving up you! The negative charged particles extend down from the cloud in "steps" and form a step leader. When it gets close enough to the ground or a tall object filled with positive particles, a channel is formed and an electrical transfer takes place. There can be several "strokes" which you see as flickering light. The channel heats to about 30,000 degrees Fahrenheit!. The rapid expansion of the heated air around the channel breaks the sound barrier, and you hear thunder.


One lightning stoke can generate between 100 million and 1 billion volts of electricity!


Number and rank of cloud-to-ground flashes by state 2007 - 2016

Lightning Safety Awareness - An Educational Problem

While many people think they are aware of the dangers of lightning, the vast majority are not. Lightning can strike as much as 10 miles away from the rain area of a thunderstorm; that's about the distance that you are able to hear the thunder from the storm. While virtually all people take some protective actions during the most dangerous part of thunderstorms, many leave themselves vulnerable to being struck by lightning as thunderstorms approach, depart, or are nearby. Although some victims are struck directly by the lightning discharge, many victims are struck as the current moves in and along the ground.


Where are people when lightning incidents occur? The chart below gives a breakdown.

Gender of Victims: 79% Male, 21% Female

Months of Fatal Lightning Incidents


Lightning Safety

NWS Lightning Safety Web Site

Outdoor Lightning Risk Reduction When a Safe Location is not Nearby

Remember, there is NO safe place outside in a thunderstorm. If you absolutely can't get to safety, this section may help you slightly lessen the threat of being struck by lightning while outside.  Don't kid yourself--you are NOT safe outside.

Being stranded outdoors when lightning is striking nearby is a harrowing experience. Your first and only truly safe choice is to get to a safe building or vehicle. If you are 
camping, climbing, on a motorcycle or bicycle, boating, scuba diving, or enjoying other outdoor activities and cannot get to a safe vehicle or building, follow these last resort tips. They will not prevent you from being struck by lightning, but may slightly lessen the odds.

  • Know the weather patterns of the area. For example, in mountainous areas, thunderstorms typically develop in the early afternoon, so plan to hike early in the day and be down the mountain by noon.
  • Listen to the weather forecast for the outdoor area you plan to visit.  The forecast may be very different from the one near your home. If there is a high chance of thunderstorms, stay inside.

These actions may slightly reduce your risk of being struck by lightning:

  • If camping, hiking, etc., far from a safe vehicle or building, avoid open fields, the top of a hill or a ridge top.
  • Stay away from tall, isolated trees or other tall objects. If you are in a forest, stay near a lower stand of trees.
  • If you are camping in an open area, set up camp in a valley, ravine or other low area. Remember, a tent offers NO protection from lighting.
  • Stay away from water, wet items (such as ropes) and metal objects (such as fences and poles). Water and metal are excellent conductors of electricity. Remember, lightning can strike up to 10 miles from the rain area. Plus the current from a lightning flash can easily travel for long distances





* Stay there! The best protection from lightning is a house or other substantial building. However, stay away from windows, doors, and metal pipes.

* Do not use electric appliances during the storm. Turn off sensitive equipment such as televisions, VCR's, and computers.

* Telephone use is the leading cause of indoor lightning injuries in the United States. Do not make a call unless it is an emergency.

Excessive Heat - Another Underrated Problem

Many people do not realize how deadly a heat wave can be. In contrast to the visible, destructive, and violent nature of floods, hurricanes, and tornadoes, a heat wave is a "silent killer". In 1995 alone, 1021 Americans perished in heat waves, including 633 in Illinois and 57 in Missouri.

The Centers for Disease Control and Prevention (CDC) reports that for the period 1979 - 2002, excessive heat exposure due to weather conditions caused 4780 deaths in the United States. That produces an average of 208 deaths a year from excessive heat. That is more that double the current 30 year average of deaths from flooding (92), the current leader in other weather related deaths.


What is a Heat Wave?
A heat wave is a period of excessive heat lasting two days or more that leads to illnesses and other stresses on people with prolonged exposure to these conditions. High humidity, which often accompanies heat in Missouri, can make the effects of heat even more harmful. While heat related illness and death can occur due to exposure to intense heat in just one afternoon, heat stress on the body has a cumulative effect. Consequently, persistence of a heat wave increases the threat to public health.

The Urban Heat Problem

Most heat-related deaths occur in cities. Brick and mortar buildings, asphalt streets, and tar roofs absorb daytime heat and slowly release it at night. Consequently, temperatures in urban areas can be warmer than rural areas by several degrees both day and night. Some basic comparisons done buy the staff at the NWS St. Louis has found that the temperature in the City of St. Louis often averages about 2 - 5 degrees higher than the temperature at Lambert St. Louis International Airport. higher This is commonly called the urban "heat island" effect. In addition to the burden of heat, stagnant conditions often develop during heat waves, with pollutants increasing in concentration near the ground and contributing further to public health problems during heat waves.

Socioeconomic factors also place urban residents under extra risk. Some people in cities do not have air conditioning, while people in high crime areas may be afraid to open their windows or venture out to cooler public buildings.

Who is Most Vulnerable During a Heat Wave?

The elderly population segment is the most vulnerable to the dangers of heat. Of the 522 deaths that occurred in Chicago during the July 12-16, 1995 heat wave, 371 (73 percent) were age 65 or older. The elderly suffer due to the diminished ability to perspire. Since the function of perspiration is to provide evaporation, which in turn provides cooling, the elderly have a reduced capacity to release heat from the body.

In addition to the elderly, infants, young children, and people with chronic health problems (especially pre-existing heart disease) or disabilities are more vulnerable to the effects of heat waves. People who are not acclimated to hot weather, overexert themselves, are obese, or use alcohol or drugs (including drugs such as antipsychotics, tranquilizers, antidepressants, certain types of sleeping pills, and drugs for Parkinson's disease) are at great risk. (Source- Centers for Disease Control and Prevention-Morbidity and Mortality Weekly Report)


Measuring the Combined Effects of Heat and Humidity


The National Weather Service uses the Heat Index (HI) to compute the "apparent temperature," which is a measure of how hot it feels to people at a certain combination of temperature and humidity. The heat index values used in forecasts, advisories, and warnings assume an average size adult, with light clothing, in the shade, with a 5 mile per hour wind. Being in full sun, or in an area with little air movement, can increase the apparent temperature, and thus increase the risk for adverse effects from the heat and humidity. Winds greater than 5 miles per hour usually enhance evaporative cooling and decrease the apparent temperature and the health threat from the heat. As noted, the impacts of heat are cumulative over time. The greatest number of heat-induced illnesses and fatalities usually peak two days after the maximum heat index values occurred.

Heat Index


The Heat Index (Apparent Temperature) can be found by taking the temperature (number on the left) and relative humidity value (number at the top) and matching them on this table. For example, a temperature of 90 degrees Fahrenheit and a relative humidity of 45 percent gives you a heat index of 93 degrees.




NWS St. Louis Excessive Heat Advisory/Warning criteria. Note: Heat Index = HI

Excessive Heat Advisory: The HI is expected to be around 105 degrees F, or the HI will range from 100 to 104 for at least 4 consecutive days.

Excessive Heat Warning: The HI is expected to be around 110 degrees F, or will be around 105 for at least 4 consecutive days.  

An Excessive Heat Watch will be issued if it appears warning criteria may be met in the near future. The 4 consecutive day criteria takes into acount the duration of an event which can be just as dangerous as a single very hot day.



Download a Heat Card in pdf format.

Common Heat Related Disorders

Heat Disorder Symptoms First Aid
Heat Camps Painful spasms usually in muscles of legs and abdomen due to heavy exertion. Heavy sweating.

Stop activity and rest in a cool place. Lightly stretch or gently massage muscle to relieve spasms. Give sips of cool water.

Heat Exhaustion Heavy sweating. Skin cool, pale, and clammy. Pulse fast and weak. Breathing fast and shallow. Fainting, dizziness, vomiting, and nausea.

Get victim to a cool place. Have him/her lie down and loosen clothing. Apply cool, moist cloths. Give sips of cool water.

Heat Stroke

Temperature 103 or higher. No sweating, rapid pulse, fast and shallow breathing. Hot, red, dry skin. Nausea, dizziness, headache, confusion.


Heat stroke is a severe medical emergency. Summon emergency assistance or get the victim to a hospital. Delay can be fatal. Move the victim to a cooler environment. Use cool baths or sponging to reduce body temperature.




Excessive Heat Safety

* Drink plenty of water and natural fruit juices, even if you're not thirsty. Avoid alcoholic beverages and drinks with caffeine, such as coffee, tea, and colas.

* Wear loose-fitting, lightweight, light-colored clothing. If you must go out, use sunscreen and wear a wide-brimmed hat. Remember that sunburn reduces the skin's ability to provide cooling.


* Avoid going out during the hottest times of the day. Take frequent breaks if working during the heat of the day.


* Using a buddy system between co-workers in high heat-stress jobs can help ensure that signs of heat stress do not go unnoticed.


* Inside during the day, keep shades drawn and blinds closed. Use air conditioning whenever available. Even just two hours per day in air conditioning can significantly reduce the risk of heat-related illness.


* Fans should only be used in a ventilated room. Blow hot air out a window with a fan during the day, and blow in cooler air at night.


* Take cool (not icy cold) baths or showers. Eat frequent, small meals. Avoid high protein foods, which increase metabolic heat. Fruits, vegetables, and salads constitute low protein meals.


* Do not leave children or pets in a closed vehicle with the windows up. Temperatures inside a closed vehicle can reach over 140 degrees within minutes.


* Provide extra water and access to a cool environment for pets.


* Listen to NOAA Weather Radio or media sources to keep up with the latest heat watches, warnings, and advisories.


For more excessive heat safety information, visit the Frequently Asked Questions on the CDC website.