When the National Weather Service (NWS) issues a heat warning, it’s something to take seriously. There are four types of warnings that could be given within a period of consecutive hot days. But before explaining what each warning means, some terms need to be defined. Temperature is “the degree or intensity of heat present in a substance or object.” Humidity is “the state or quality of being humid. It’s a quantity representing the amount of water vapor in the atmosphere or gas.” If we put both the temperature and humidity together, we get what is called the heat index. The heat index “the apparent temperature” or “what the temperature feels like to the human body” (Merriam Webster Dictionary). This number is calculated by knowing the air temperature and relative humidity. It’s easy to figure out what the heat index is by using a chart that the NWS made. But, for example, if it is 90 degrees Fahrenheit outside, and the relative humidity is 65%, then the heat index would be 103 degrees.
So it all begins with an excessive heat outlook. These are issued when the next 3-7 days are forecasted to be upwards of 100 degrees Fahrenheit, allowing people to get prepared for the intense heat wave that is coming through. The next step the NWS would take is to issue an excessive heat watch. Watches are different from outlooks because it means that the weather is favorable for that event within the next 24-72 hours. The wide range in the 24-72 is because the exact timing of the heat or heat wave is uncertain at that point of time of forecasting, but confident enough that it will hit during the 24-72 hour period.
You want to take action when a heat advisory is issued. This type of warning is released within 12 hours of the hot weather that could be potentially dangerous. In most parts of the United States, hot weather that is potentially hazardous consists of at least two days with the heat index temperature above 100 degrees Fahrenheit, and at night where the temperature doesn’t drop below 75 degrees. The NWS adds that “these criteria vary across the country, especially for areas that are not used to dangerous heat conditions.” This type of warning is sent out for people to take actions and plan accordingly so that they don’t become ill during this period of heat.
The most severe heat warning issued is called an excessive heat warning. This is basically the same thing as a heat advisory, but the main difference is that heat index temperatures are expected to be upwards of 105 degrees Fahrenheit, with nighttime temperatures not dropping below 75 degrees. This again, varies for different locations across the US, as explained before.
It’s essential to watch and understand all of these warnings issued by the NWS because they could impact your health. When outside, make sure that you’re staying hydrated and taking breaks from any work you could be doing. Make sure never to leave any kids or pets unattended in cars, and always check up on those who are elderly, sick, or without air conditioning.
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© 2018 Weather Forecaster Allison Finch