PHOENIX - An excessive heat warning in Phoenix is a little different than most places.

That's because if the city went by the same criteria as other places, there's a good chance Phoenix would be under an excessive heat warning all summer.

Extreme heat is imminent 

Extreme heat warnings in Phoenix are based on a special computer model and not the same criteria that some of the other NWS offices use.

The computer model measures heat impact levels and the dangers they pose to people. The algorithm will factor in both the forecast high and low temperatures.

If that calculation produces a number that crosses over the "extreme" threshold - aka the 95th percentile - a warning is issued.

READ: Excessive heat warnings are a little different in Phoenix

Everyone needs to be prepared

Dangerous signs to watch out for if you're out in the heat too long are cramps, exhaustion, cool, wet, pale skin and headaches or dizziness. In the worst cases, these symptoms can lead to heat stroke.

READ: Phoenix is about to get very hot. What are the signs of heat stroke?

To stay safe, try to stay inside as much as possible, drink a lot of water and avoid alcohol, sugary drinks, and caffeine.