NWS Phoenix Heat Page

Heat is the deadliest weather in Arizona. During Arizona's hottest months, the NWS issues alerts to notify the public when unusually hot weather is expected. These alerts are intended to raise awareness and prevent heat illness and death from occurring and mitigate financial impacts. When the NWS issues an alert, it should serve as a signal that on that day it is not "business as usual."

Collaborative research with the Centers for Disease Control and Prevention (CDC) shows that heat-associated deaths in Arizona can occur with temperatures in the mid 80s and hotter. Research also shows that our bodies have a greater ability to tolerate heat as the summer wears on, known as acclimation. For example, a temperature of 105 °F in May will seem hot, whereas the same temperature in June or July will not seem as hot because our bodies have acclimated to the heat. Hence, there is not one single, constant temperature used to determine when an alert will be issued. In order to better address heat risk and allow you to prepare for upcoming heat events, the NWS developed the experimental HeatRisk product.

HeatRisk provides a quick view of potentially impactful heat conditions over the upcoming seven days based on how much above normal high and low temperatures are, the duration of unusual heat, and humidity (as represented by overnight low temperatures). HeatRisk is portrayed in a numeric (0-4) and color (green/yellow/orange/red/magenta) scale which is similar in approach to the Air Quality Index (AQI) or the UV Index. It provides one value each day that indicates the approximate level of heat risk concern for any location, along with identifying the groups who are most at risk. This product is complementary to the official NWS Watch/Warning/Advisory program and is meant to provide continuously available heat risk guidance for those decision makers and heat sensitive populations who need to take actions at levels that may be below current NWS heat product levels.

HeatRisk temperature thresholds for Phoenix Sky Harbor International Airport. Click image for full version. Other locations available here.

When "High" or "Very High" HeatRisk conditions are forecast, an Excessive Heat Watch or Excessive Heat Warning will be issued. An Excessive Heat Watch conveys a moderate (50%) confidence that excessive heat will occur. If confidence increases to a high (80%+) level, an Excessive Heat Warning is issued. An exception would be in the case of a mixture of periods of recommended Warnings and Advisories, where forecaster discretion and coordination with surrounding offices should determine the appropriate Legacy Product and messaging strategy. Both alerts are a way to give public and emergency officials a "heads up" that extreme temperatures are expected. Additional information may be found here. Note that many lower elevation locations across the Southwest which experience chronic heat do not receive the lesser Heat Advisory alert.

Based on an analysis of emergency room visits across Maricopa County during 2020, it was found that HeatRisk categories accurately describe the level of heat-related illness. During the hottest days, with "High" and "Very High" HeatRisk categories, spikes in ER visits were noted. These days were generally coincident with the issuance of Excessive Heat Warnings. For lower risk days, ER visits were still noted but to a lesser degree. When averaging by HeatRisk category, there is a steady increase in ER visits for heat-related illness as intensity levels increase. Notably, heat-related illness was observed even on "Low" days, clearly indicating that even without official alerts heat can pose a significant health threat if precautions are not taken.

A similar analysis of heat-related emergency calls received by the City of Phoenix Fire Department shows a clear connection between call volume and HeatRisk category. During 2022, the largest spikes in calls were coincident with episodes including "High" and "Very High" HeatRisk levels. Averaged by HeatRisk category (inset), a clear stepwise function is revealed. Notably, calls are still received even on "Low" days, supporting continued risk to very sensitive groups.

Preventing Heat-Related Illness

Your body keeps itself cool by letting heat escape through the skin, and by evaporating sweat (perspiration). If your body does not cool properly or does not cool enough, you might suffer from a heat-related illness.

Anyone can be susceptible to heat-related illness. Those at greatest risk are infants and young children, adults over 65, people who are homeless, people who are overweight, people who overexert during work or exercise, and people who are physically ill or on certain medications, such as for depression, insomnia, or poor circulation. Heat-related illness may be serious or even deadly if unattended.

Staying healthy during the summer is easier if you take the time to protect yourself by making sure you are drinking enough water and limiting your exposure to the heat. Follow these simple rules:

• Drink water. Even people that stay mostly indoors all day should drink at least 2 liters of water per day. People that spend time outdoors should drink 1 to 2 liters per hour that they are outdoors. People that do strenuous activity outdoors should be very careful, being your body can lose up to 4 liters of water per hour during strenuous activity. You should carry water with you and drink even if you do not feel thirsty. Be heat safe and avoid alcohol, which dehydrate the body. Avoid using salt tablets unless directed to do so by a physician.
• Dress for the heat. Wear lightweight, light-colored clothing. Light colors will reflect away some of the sun's energy. It is also a good idea to wear hats or to use an umbrella. Always apply sunscreen to exposed skin.
• Eat small meals and eat more often. Avoid foods that are high in protein which increase metabolic heat.
• Monitor Those at High Risk. Check on friends, family, and neighbors for signs of heat exhaustion or heat stroke. Infants and young children, of course, need much more frequent watching.
• Slow down. Avoid strenuous activity. If you must do strenuous activity, do it during the coolest part of the day, which is usually in the morning between 4:00 a.m. and 7:00 a.m.
• Stay indoors when possible.
• Take regular breaks when engaged in physical activity on warm days. Take time out to find a cool place. If you recognize that you, or someone else, are showing symptoms of a heat-related illness, stop activity and find a cool place. Remember, have fun, but stay cool!

Signs & Symptoms of Heat-Related Illness

When temperatures are on the rise, watch for the following symptoms:

• Thirst: By the time your body tells you that you are thirsty, you are already mildly dehydrated.
• Heat cramps: Heat cramps are muscular pains and spasms due to heavy exertion. They usually involve the abdominal muscles or the legs. The loss of water and salt from heavy sweating causes heat cramps.
• Heat Exhaustion: Heat exhaustion is less dangerous than heat stroke. It typically occurs when people exercise heavily or work in a warm, humid place where body fluids are lost through heavy sweating. Fluid loss causes blood flow to decrease in the vital organs, resulting in a form of shock. With heat exhaustion, sweat does not evaporate as it should, possibly because of high humidity or too many layers of clothing. As a result, the body is not cooled properly. Signals include cool, moist, pale, flushed or red skin; heavy sweating; headache; nausea or vomiting; dizziness; and exhaustion. Body temperature will be near normal.
• Heat Stroke: Also known as sunstroke, heat stroke is life-threatening. The victim's temperature control system, which produces sweating to cool the body, stops working. The body temperature can rise so high that brain damage and death may result if the body is not cooled quickly. Signals include hot, red and dry skin; changes in consciousness; rapid, weak pulse; and rapid, shallow breathing. Body temperature can be very high—sometimes as high as 105 °F.

Stages of Heat-Related Illness

Heat-related illness usually comes in stages. The signal of the first stage is thirst. Drinking water at this stage can prevent you from progressing to the more serious kinds of heat related illnesses. The next stage is muscle cramps. These cramps can be mild or very painful. If you are caring for a person who has heat cramps, have him or her stop activity and rest. If the person is fully awake and alert, have him or her drink small amounts of cool water or a commercial sports drink. Gently stretch the cramped muscle and hold the stretch for about 20 seconds, then gently massage the muscle. Repeat these steps if necessary. If the victim has no other signals of heat-related illness, the person may resume activity after the cramps stop.

The signals of the next, more serious stage of a heat-related illness (often called heat exhaustion) include:

• Cool, moist, pale skin (the skin may be red right after physical activity).
• Headache.
• Dizziness and weakness or exhaustion.
• Nausea.
• The skin may or may not feel hot.

The warning signs of the most serious stage of a heat-related illness (often called heat stroke or sun stroke) vary but may include:

• Vomiting.
• Confusion.
• Throbbing headache.
• Decreased alertness level or complete loss of consciousness.
• High body temperature (sometimes as high as 105 °F).
• Skin may still be moist or the victim may stop sweating and the skin may be red, hot and dry.
• Rapid, weak pulse.
• Rapid, shallow breathing.
• Seizures.

NOTE: Heat stroke is life threatening. Call 9-1-1 or the local emergency number if you are suffering from any of the above symptoms.

General Care for Heat Emergencies

General care for heat emergencies include cooling the body, giving fluids, and minimizing shock. For specific heat-related emergencies, follow these steps:

• For heat cramps or heat exhaustion: Get the person to a cooler place and have the person rest in a comfortable position. If the person is fully awake and alert, give a half glass of cool water every 15 minutes. Do not let him or her drink too quickly. Do not give liquids with alcohol in them, as they can make conditions worse. Remove or loosen tight clothing and apply cool, wet cloths such as towels or wet sheets or mist with water. Get the person into an air conditioned space if possible. Call 9-1-1 or the local emergency number if the person refuses water, vomits or loses consciousness.
• For heat stroke: Heat stroke is a life-threatening situation! Help is needed fast. Call 9-1-1 or your local EMS number. Move the person to a cooler place. Quickly cool the body using any means available, including cool water and ice. If you have ice packs or cold packs, wrap them in a cloth and place them on each of the victim's wrists and ankles, in the armpits and on the neck to cool the large blood vessels. (Do not use rubbing alcohol because it closes the skin's pores and prevents heat loss.) Wrap wet sheets around the body and place the person in front of a fan or air conditioner. Watch for signals of breathing problems and make sure the airway is clear. Keep the person lying down.

Additional Resources:
ADHS Extreme Weather & Public Health | CalOES Summer Heat Resources | CDC Extreme Heat | EPA Extreme Heat

Phoenix, AZ Area

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2019 (24): Jun 11 to Jun 13, Jul 11 to Jul 12, Jul 15 to Jul 16, Jul 27 to Jul 28, Aug 3 to Aug 5, Aug 13 to Aug 16, Aug 20 to Aug 21, Aug 27 to Aug 28, Aug 30 to Aug 31, Sep 4, Sep 7

2018 (16): May 6, Jun 3 to Jun 4, Jun 12 to Jun 13, Jun 21 to Jun 22, Jul 5 to Jul 6, Jul 23 to Jul 25, Aug 6 to Aug 7, Sep 14 to Sep 15

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2015 (13): Jun 16 to Jun 21, Aug 4 to Aug 5, Aug 13 to Aug 17

2014 (7): Jun 2 to Jun 4, Jul 23 to Jul 24, Jul 30 to Jul 31

2013 (14): Jun 2, Jun 7, Jun 12, Jun 28 to Jul 3, Aug 1, Aug 16 to Aug 18, Aug 20

2012 (20): May 21 to May 22, May 31 to Jun 1, Jun 18, Jun 27 to Jun 30, Jul 9 to Jul 10, Aug 6 to Aug 14

2011 (22): Jun 22, Jun 27 to Jun 29, Jul 1 to Jul 3, Aug 2 to Aug 3, Aug 18, Aug 22 to Sep 1, Sep 4

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Yuma, AZ Area

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2020 (39): Apr 26 to Apr 30, May 6 to May 7, May 27 to May 29, Jun 3 to Jun 4, Jul 11 to Jul 13, Jul 19, Jul 30 to Aug 3, Aug 13 to Aug 20, Aug 24 to Aug 28, Sep 4 to Sep 7, Sep 17

2019 (18): Jun 11 to Jun 13, Jul 15 to Jul 16, Aug 3 to Aug 5, Aug 13 to Aug 16, Aug 20 to Aug 21, Aug 30 to Aug 31, Sep 4

2018 (11): May 6, Jun 13, Jun 22, Jul 5 to Jul 6, Jul 23 to Jul 25, Jul 26, Aug 6, Sep 8

2017 (16): May 23, Jun 17 to Jun 26, Jul 7, Aug 27 to Aug 30

2016 (9): Jun 3 to Jun 5, Jun 19 to Jun 22, Jul 22 to Jul 23

2015 (13): Jun 16 to Jun 21, Aug 4 to Aug 5, Aug 13 to Aug 17

2014 (5): Jul 23 to Jul 24, Jul 30 to Jul 31, Aug 30

2013 (8): Jun 7, Jun 28 to Jul 3, Aug 17

2012 (17): May 13, May 14, May 21 to May 22, May 31 to Jun 1, Jun 18, Jul 9 to Jul 11, Aug 8 to Aug 14

2011 (8): Jun 28, Jul 2 to Jul 3, Aug 2 to Aug 4, Aug 29, Sep 8

2010 (6): Jul 17 to Jul 18, Aug 24 to Aug 25, Sep 3 to Sep 4

2009 (16): Jul 11 to Jul 14, Jul 17 to Jul 20, Jul 26 to Jul 28, Aug 5, Aug 27 to Aug 30

2008 (23): May 18 to May 20, Jun 14 to Jun 23, Jun 30 to Jul 3, Jul 18, Aug 1 to Aug 2, Sep 6

2007 (3): Jul 4 to Jul 5, Aug 29

2006 (7): Jun 3 to Jun 4, Jul 14 to Jul 15, Jul 21 to Jul 23

El Centro, CA Area

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2021 (23): Jun 14 to Jun 20, Jun 27 to Jun 28, Jul 9 to Jul 12, Aug 3 to Aug 5, Aug 25 to Aug 29, Sep 12 to Sep 13

2020 (38): Apr 26 to Apr 30, May 6 to May 7, May 27 to May 29, Jun 3 to Jun 4, Jul 11 to Jul 13, Jul 30 to Aug 3, Aug 13 to Aug 20, Aug 24 to Aug 28, Sep 4 to Sep 7, Sep 17

2019 (21): Jun 11 to Jun 12, Jul 12 to Jul 16, Jul 27 to Jul 28, Aug 3 to Aug 5, Aug 13 to Aug 16, Aug 20 to Aug 21, Aug 30 to Aug 31, Sep 4

2018 (15): May 6, May 9, Jun 3 to Jun 4, Jun 13, Jun 22, Jul 6, Jul 23 to Jul 27, Aug 6 to Aug 7, Sep 8

2017 (15): May 23, Jun 18 to Jun 26, Jul 7, Aug 27 to Aug 30

2016 (15): Jun 3 to Jun 5, Jun 19 to Jun 22, Jun 29, Jul 22 to Jul 23, Jul 27 to Jul 28, Aug 15 to Aug 17

2015 (13): Jun 16 to Jun 21, Aug 4 to Aug 5, Aug 13 to Aug 17

2014 (5): Jul 23 to Jul 24, Jul 30 to Jul 31, Aug 30

2013 (8): Jun 7, Jun 28 to Jul 3, Aug 17

2012 (17): May 13 to May 14, May 21 to May 22, May 31 to Jun 1, Jun 18, Jul 9 to Jul 11, Aug 8 to Aug 14

2011 (5): Jun 28, Jul 2, Aug 29, Aug 31, Sep 8

2010 (6): Jul 17 to Jul 18, Aug 24 to Aug 25, Sep 3, Sep 4

2009 (16): Jul 11 to Jul 14, Jul 17 to Jul 20, Jul 26 to Jul 28, Aug 5, Aug 27 to Aug 30

2008 (20): May 18 to May 20, Jun 14 to Jun 23, Jun 30 to Jul 3, Jul 18, Aug 1 to Aug 2, Sep 6

2007 (3): Jul 4 to Jul 5, Aug 29

2006 (7): Jun 3 to Jun 4, Jul 14 to Jul 15, Jul 21 to Jul 23

Local climate information available here.