Extreme Heat

The extreme heat hazard in Linn County is often underestimated because other natural hazards occur more frequently and its effects can vary based on vulnerable population within the County. 

Extreme heat is defined by temperatures that hover 10 degrees or more above the average high temperature for the region and last for several weeks are defined as extreme heat. Humid or muggy conditions, which add to the discomfort of high temperatures, occur when a "dome" of high atmospheric pressure traps hazy, damp air near the ground. Excessively dry and hot conditions can provoke dust storms and low visibility. Droughts occur when a long period passes without substantial rainfall. A heat wave combined with a drought is a very dangerous situation.

During the period between January 1950 and May 2008 Linn County experienced three extreme heat events. The heat wave that occurred in July of 1995 had a major impact across the entire state, temperatures ranged from 98 degrees to 108 degrees with heat indices reaching a high of 131 degrees. This event lasted two days causing almost four million dollars of property damage and resulted in three fatalities state wide. 

Elderly persons, small children, chronic invalids, those on certain medications or drugs (especially tranquilizers and anticholinergics), and persons with weight and alcohol problems are particularly susceptible to heat reactions.  Healthy individuals working outdoors in the sun and heat are vulnerable as well. Individuals and families with low budgets as well as inner city dwellers can also be susceptible due to poor access to air-conditioned rooms.

The Heat Index chart is a tool which accurately measures apparent temperature of the air as it increases with the relative humidity. The Heat Index can be used to determine what effects the temperature and humidity can have on the population. To determine the Heat Index, you need the temperature and the relative humidity. Once both values are known, the Heat Index will be the corresponding number with both values. That number provides how it really feels. It is important to know that the Heat Index (HI) values are devised for shady, light wind conditions. Exposure to full sunshine can increase HI values by up to 15 degrees. Also, strong winds, particularly with very hot, dry-air can be extremely hazardous to individuals.

Health Hazard 



Redness and pain. In severe cases: swelling of skin, blisters, fevers, and headaches. 


Excessive thirst, dry lips and slightly dry mucous membranes 

Heat Cramps 

Painful spasms, usually in muscles of legs and abdomen, and possible heavy sweating 

Heat Exhaustion 

Heavy sweating; weakness; cold, pale and clammy skin; weak pulse; possible fainting and vomiting 

Heat Stroke 

High body temperature (104ºF or higher), hot and dry skin, rapid and strong pulse, and possible coma 


Source: NOAA


© 2009 Linn County EMA


Excessive Heat Watch: 

The National Weather Service issues and Excessive Heat Watch within 24 to 48  hours of the onset of the following conditions: heat index of at least 105°F for more than 3 hours per day for 2 consecutive days, or a heat index of at least 115°F for any period of time.

Excessive Heat Warning:

The National Weather Service issues an Excessive Heat Warning within 24 hour of the onset of the following conditions: heat index of at least 105°F for more than 3 hours per day for 2 consecutive days, or a heat index of more than 115°F for any time period.


Extreme Heat Safety Tips

Slow down. Strenuous activities should be reduced, eliminated, or rescheduled to the coolest time of the day. Individuals at risk should stay in the coolest available place, not necessarily indoors.

Dress for summer. Lightweight light-colored clothing reflects heat and sunlight, and helps your body maintain normal temperatures.

Put less fuel on your inner fires. Foods (like proteins) that increase metabolic heat production also increase water loss.

Drink plenty of water or other non-alcohol fluids. Your body needs water to keep cool. Drink plenty of fluids even if you don’t feel thirsty. Persons who (1) have epilepsy or heart, kidney, or liver disease, (2) are on fluid restrictive diets or (3) have a problem with fluid retention should consult a physician before increasing their consumption of fluids.

Do not drink alcoholic beverages.

Do not take salt tablets unless specified by a physician.

Spend more time in air-conditioned places. Air conditioning in homes and other buildings markedly reduces danger from the heat. If you cannot afford an air conditioner, spending some time each day (during hot weather) in an air conditioned environment affords some protection.

Source: NOAA


Links or references to individuals or companies does not constitute an endorsement  or guarantee of any information, product, or service you may receive from such sources.

Linn County Emergency Management Agency, 6301 Kirkwood Blvd. S.W., Cedar Rapids, Iowa 52404