National Weather Service United States Department of Commerce

Heat in the Southwest



Excessive Heat Watches/Warnings


Excessive Heat Watch Prepare. Extreme heat is expected within the next two to seven days.

Excessive Heat Warning Act! Extreme heat is occurring or imminent.

Heat is the deadliest weather in Arizona.

During Arizona's hottest months, the National Weather Service issues weather 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."

Research from 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. For example, a temperature of 105 degrees 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. Instead, the NOAA/NWS HeatRisk product is leveraged to identify unusually hot days.

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. Both alerts are a way to give public and emergency officials a "heads up" that extreme temperatures are expected.


Safety Information


The negative effects of excessive heat can be easily avoided. Some simple steps you can take include:

  • Slow down. Strenuous activities should be reduced, eliminated, or rescheduled to the coolest time of the day. Individuals at risk should stay in the coolest available place, not necessarily indoors.
  • Dress for summer. Lightweight light-colored clothing reflects heat and sunlight, and helps your body maintain normal temperatures.
  • Put less fuel on your inner fires. Foods (like proteins) that increase metabolic heat production also increase water loss.
  • Drink plenty of water or other non-alcohol fluids. Your body needs water to keep cool. Drink plenty of fluids even if you don't feel thirsty. Persons who (1) have epilepsy or heart, kidney, or liver disease, (2) are on fluid restrictive diets or (3) have a problem with fluid retention should consult a physician before increasing their consumption of fluids.
  • Spend more time in air-conditioned places. Air conditioning in homes and other buildings markedly reduces danger from the heat. If you cannot afford an air conditioner, spending some time each day (during hot weather) in an air conditioned environment affords some protection.
  • Don't get too much sun. Sunburn makes the job of heat dissipation that much more difficult.

For additional safety information...
Center for Disease Control and Prevention - Extreme Heat
Environmental Protection Agency - Extreme Heat
Arizona Dept. of Health Services - Extreme Weather and Public Health
State of California Office of Emergeny Services - Summer Heat Resources


Statistics on Heat Impacts

Contrary to common perception, heat is the number one weather-related killed in the United States. According to data from the Center for Disease Control and Prevention (CDC)[source], heat-related deaths numbered 8,081 in the United States from 1999 to 2010. On average, more people are killed by heat in the U.S. than are by tornadoes, hurricanes, floods, and lightning combined (see graphic below).

In Arizona, heat-related deaths are by far the number one weather-related killer. In Maricopa County, where the majority of the Phoenix metropolitan area is located, an average of 70+ people die each year with heat being a contributing factor[source]. Preliminary data for 2019 place that number close to 200.

Source: NOAA, CDC


Climatology of Heat in the Southwest


The southwest United States is one of the hottest areas of the United States. Temperatures in the triple-digits are common for several months of the year. In addition, the rapid expansion of major urban areas in Phoenix has caused a significant urban heat island (UHI) to develop - causing low temperatures to be abnormally high. The table below compares the frequency of extreme temperatures at select locations in the NWS WFO Phoenix County Warning Area.


  Phoenix Coolidge Parker El Centro Area Yuma Globe
Average Number of Days w/High of 100+ °F per Year # 110 117 107 111 118 19
Average Number of Days w/High of 110+ °F per Year # 19 27 39 16 26 0
Average Number of Days w/Low of 80+ °F per Year # 67 10 37 29 59 0
All-Time Record High Temperature 122 °F
123 °F
127 °F
122 °F
124 °F
113 °F
All-Time Record High Low Temperature 96 °F
96 °F
100 °F
98 °F
94 °F
86 °F
# Based on 1981-2010 data. * And previous years.


Historical Excessive Heat Warnings for the Phoenix Area


2005 (11): May 20-23, June 22, July 13, July 17-18, August 28-30

2006 (8): June 3-5, July 14-15, July 21-23

2007 (7): June 21, July 4-5, August 12-14, August 29

2008 (13): May 18-20, June 14-22, July 1-4, July 18, July 31-August 2

2009 (21): July 11-14, July 17-20, July 26-29, August 1-5, August 27-30

2010 (36): June 6-7, June 30-July 2, July 8-10, July 13-17, July 19-31, August 4-6, August 13-15, August 23-25, September 3

2011 (24): June 22, June 27-29, July 1-3, August 2-3, August 18, August 22-September 4

2012 (21): May 21-22, May 31-June 1, June 18, June 27-30, July 9-10, August 6-14

2013 (14): June 7, June 12, June 28-July 3, August 1, August 16-19, August 20

2014 (6): June 2-4, July 23-24, July 30

2015 (12): June 16-22, August 4-5, August 14-16

2016 (11): June 3-6, June 19-23, July 22-23

2017 (19): June 4-7, June 17-26, July 5-7, August 29-30

2018 (16): May 6, June 3-4, June 12-13, June 21-22, July 5-6, July 23-25, August 6-7, September 14-15

2019 (25): June 11-13, July 11-16, July 27-28, August 3-5, August 13-16, August 20-21, August 27-28, August 30-31, September 4, September 7

2020 (through June 4th) (15): April 26-30, May 6-7, May 27-31, June 2-4