When heat turns deadly: A guide to official advisories, warnings

Annie Vong, Las Vegas Review-Journal on

Published in Weather News

What’s the difference between a heat advisory, a heat watch and heat warnings?

The three types of warnings are like steps on a ladder, says Nick Novella, a forecaster for NOAA’s Climate Prediction Center.

At the bottom rung is a heat watch, with the possibility of an excessive heat event in the next 24 to 72 hours. Whether it will occur and exactly when it will occur is uncertain.

One rung up is a heat advisory, when conditions are expected to be favorable for a heat event,” says Novella.

Advisories are issued within 12 hours of dangerous heat conditions, where the heat index values are predicted to be over 100 for 2 days and overnight air temperatures will not drop under 75 degrees.

The highest rung of the ladder is heat warnings or excessive heat warnings.

“The heat warning or excessive heat warning, is the most severe,” said Novella. Heat warnings indicated that sometime within the next 12 hours, heat index values may reach over 105 degrees and that overnight temperatures will not drop below 75 degrees.

Overnight heat is dangerous, Novella said, pointing to Phoenix as an example of an area whose overtime temperatures never got below 95 degrees.


“Most people tend to concern themselves with the daytime temperatures because they’re hot … Overnight heat can be dangerous because it prevents any kind of relief during the from the high temperatures during the day,” adds Novella.

Daytime temperatures are not the only records being broken during a heat wave.

“We see that minimum temperature records are being broken just as much as the maximum daytime temperatures,” Novella said. “It’s important for the public to know that they should be looking at the weather service forecast page and the local forecast page to see if such an event is coming.”

Dr. Ketan Patel, Medical Director of UMC’s Adult Emergency Department stresses the seriousness of extreme heat events.

“When you have extremes of heat, that heat acts as a stressor, and that stress can be a trigger more things in those patients who are more susceptible to it,” says Patel.

“Stress like heat, extreme cold or something else can be the trigger for heart attacks, for a stroke, for decreased immune functions that results in a subsequent illness,” adds Patel. “You need to be attuned to what you’re feeling and going through to seek care early.”


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