When is an excessive heat warning issued in Arizona?

PHOENIX (3TV/CBS 5) – The Phoenix Fire Department says a woman overheated and had to be taken to the hospital after they rescued her from Camelback Mountain just before noon today. The temperature at that time was already over 100 degrees.

The summer months are usually the busiest for mountain rescues. Just last year, the City of Phoenix began shutting down some popular hiking trails during the summer when the National Weather Service issued an excessive heat warning. With a high temperature of 112 Monday, we’ve had some viewers reach out to Arizona’s Family and ask why the trails are open and does this put the first responders at risk.

The trails have not closed yet this year, but we found out that meteorologists look into a few different factors before deciding to issue a warning, like how much warmer temps are compared to normal and the risk the heat poses to the community.

So we looked into what it takes to issue this type of heat warning and the threat the heat can pose to the community. Sunday and Monday, temperatures were the warmest of the year so far. Monday into Tuesday, an Excessive Heat Warning is in effect for areas like Tucson, with temperatures expected between 105 and 113.

With a high of 112 degrees in the Valley Monday, you may be wondering why there is a warning in the south but not in the Valley. NWS meteorologist Jessica Leffel explains why. “At this time, their departures from normal are a little higher so we might not need heat warnings yet,” she said. Leffel says to issue an Excessive Heat Warning; they look at the high temperature and compare it to the average temperature for that day during that time of the year. In southern Arizona Monday, the departure from normal is much higher than here in the Valley.

The NWS will also look at this tool with four categories breaking down the heat risk from minor to extreme. Monday was a moderate risk meaning those who are outdoors for a long period of time could start to feel the impacts. “Usually when we get to major or extreme heat risk categories we will start looking at those excessive heat warnings and watches,” Leffel said.

That is something we could see looking ahead to next weekend, with temperatures expected to rise. And if an excessive heat warning is issued, people are encouraged to limit outdoor activities, including hiking. “Heat is the number one weather related killer not only in Arizona but also in the United States so make sure you’re practicing heat safety,” Leffel said.

The NWS will also consider overnight temperatures before issuing a warning. “Right now we also have those overnight recoveries and have high 70s and low 80s range so with that it helps us get a little bit of cooling overnight to keep those temperatures down but going into next weekend, we can see how those lows will vary and if we are going to have just as good overnight recoveries or not and maybe that will prompt the issuance of more products,” Leffel said.

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