Each summer, people across the country venture outside to catch up on some much-needed sun. Unfortunately, those bright rays can bring with them a danger all their own in the form of excessive heat. While enjoying the sun is a healthy practice which can often have many benefits, people of all ages should still take precautions to help stay safe from the sun’s emissions.
Four Important Heat Terms
There are four important terms relating to heat you should be familiar with:
- Heat Advisory
- Excessive Heat Outlook
- Excessive Heat Watch
- Excessive Heat Warning
What is a Heat Advisory?
Researchers at the NWS note that a heat advisory is issued 12 hours prior to excessive heat conditions. While the exact criteria can vary depending on where you live, general guidelines for a heat advisory indicate the following: when the maximum heat index temperature is expected to reach 100°F/38°C or higher for at least two days, and nighttime temperature will not drop below 75°F/24°C, this indicates conditions are favorable for a heat advisory.
In other words, when the outside temperature is expected to reach 100°F/38°C, or the heat index value is expected to reach at least 105°F/41°C within the next 24 hours, a heat advisory is issued .
During a heat advisory, the young, elderly, and those with medical conditions should use caution when outside. Keep in mind, however, if you fall into one of those categories, staying indoors as much as possible during a heat advisory is recommended. (Notably, doctors at the CDC warn that even those in good health can be affected if they participate in strenuous physical activities during a heat advisory.)
What is an Excessive Heat Outlook?
An excessive heat outlook is issued when local officials determine there will be an excessive heat event sometime in the next three to seven days. These are circulated well in advance, for those who may need extra lead time to prepare.
What is an Excessive Heat Watch?
During an excessive heat watch, outdoor conditions become more dangerous for the young, elderly, and those with medical conditions. Notably, it is not just high heat temperature that plays a factor in this advisory—it is also the heat index, which is based on humidity present in the air.
During an excessive heat watch, high temperatures are predicted; the heat index is expected to reach a high of 110°F/43°C and not fall below 75°F/24°C for at least a 48-hour period, starting in the next 12 to 48 hours.
The young, elderly, and those with medical conditions should take precautions to avoid going outdoors. Beyond that, everyone in the affected area should stay aware of weather conditions. If you do not have air conditioning, consider locating your nearest cooling shelter, or staying with family and friends with A/C. While excessive heat watches are issued at least 24 to 72 hours in advance, the heat wave’s exact timing and occurrence is still uncertain, so take caution and evaluate the risk of going outside.
What is an Excessive Heat Warning?
During an excessive heat warning, heat index values are anticipated to reach or top 110°F/43°C and not fall lower than 75°F/24°C for at least a 48-hour period, beginning in the next 24 hours. These warnings are issued within 12 hours of the excessive heat’s onset. Ultimately, when the maximum heat index temperature is expected to be 105°F/41°C or higher for at least two days, and nighttime temperatures will not drop below 75°F/24°C, that is a good indication you will be under an excessive heat warning.
Avoid strenuous or outdoor activities during the hottest time of day. If you must venture outside, drink lots of water and take breaks when needed. Still, it is advised you stay inside, in air-conditioning, as much as possible. Be sure to check on elderly friends or family members who may live alone, as conditions can prove life-threatening or even fatal.
What is a Heat Index?
The heat index (sometimes called the “HI”) combines air temperature and relative humidity to arrive at “apparent temperature”—how hot it feels to the human body.
Using a heat index chart, weather officials can estimate how hot it would feel if the humidity was some other value. The heat index is calculated by viewing the chart and locating the appropriate intersection of actual air temperature and relative humidity.
High heat index values are caused by higher than normal temperatures and humidity . Such high levels can pose a threat to human life, causing conditions like heatstroke . View the heat index chart here on the National Oceanic and Atmospheric Administration’s website.
Sources:
https://www.noaa.gov/jetstream/global/heat-index