National Weather Service United States Department of Commerce

Heat in the Southwest

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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
6-26-1990
123 °F
7-30-1995*
127 °F
7-7-1905
122 °F
7-29-1995*
124 °F
7-28-1995
113 °F
6-26-1970
All-Time Record High Low Temperature 96 °F
7-15-2003
96 °F
7-12-1909*
100 °F
7-18-1931
98 °F
8-30-1976
94 °F
8-31-1998
86 °F
8-19-1948
# Based on 1981-2010 data. * And previous years.

 

Historical Excessive Heat Warnings 

 

Phoenix Area


2008 (18): May 19-20, June 15-23, July 1-3, July 18, July 31-August 2

2009 (21): July 11-14, July 17-20, July 26-29, August 2-6, August 27-30

2010 (25): June 6-7, June 30-July 2, July 8-10, July 13-211, August 5, August 13-15, August 23-25, September 3

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

2012 (20): May 21-22, May 31-June 1, June 18, June 27-30, July 9-10, August 6-14

2013 (15): June 2, June 7, June 12, June 28-July 3, August 1, August 16-19, August 20

2014 (8): June 2-5, July 23-24, July 30-31

2015 (14): June 16-22, August 4-5, August 13-17

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 (48): April 26-30, May 6-7, May 27-31, June 2-4, July 10-13, July 19, July 29-August 4, August 9-10, August 12-20, August 24-28, September 4-7, September 17

 

Yuma

 

2008 (21): May 18-20, June 14-23, June 30-July 03, July 18, August 1-2, September 6

2009 (17): July 11-14, July 17-20, July 26-29, August 05, August 27-30

2010 (6): July 17-18, August 24-25, September 3-4

2011 (8): June 28, July 2-3, August 2-4, August 29, September 08

2012 (17): May 13-14, May 21-22, May 31-June 1, June 18, July 9-11, August 8-14

2013 (8): June 7, Jun 28-July 3, August 17

2014 (5): Jul 23, Jul 24, Jul 30, Jul 31, August 30

2015 (14): June 16-22, August 4-5, August 13-17

2016 (9): June 3-5, June 19-22, July 22-23

2017 (15): June 17-26, July 7, August 27-30

2018 (7): May 6, June 13, June 22, July 5-6, August 6, September 8

2019 (18): June 11-13, July 12, July 15-16, August 3-5, August 13-16, August 20-21, August 30-31, September 4

2020 (38): April 26-30, May 6-7, May 27-29, June 3-4, July 11-13, July 19, July 30-August 3, August 13-20, August 24-27, September 4-7, September 17

 

El Centro

 

2008 (21): May 18-20, June 14-23, June 30-July 3, July 18, August 1-2, September 6

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

2010 (6): July 17-18, August 24-25, September 3-4

2011 (5): June 28, July 2, August 4, August 29, September 8

2012 (17): May 13-14, May 21-22, May 31-June 1, June 18, July 9-11, August 8-14

2013 (8): June 7, June 28-July 3, August 17

2014 (5): July 23-24, July 30-31, August 30

2015 (14): June 16-22, August 4-5, August 13-17

2016 (15): June 3-5, June 19-22, June 29, July 22-23, July 27-28, August 15-17

2017 (13): June 18-25, July 7, August 27-30

2018 (14): May 9, June 3-4, June 13, June 22, July 6, July 23-27, August 6-7, September 8

2019 (20): June 11-12, July 12-16, July 28, August 3-5, August 13-16, August 20-21,August 30-31, September 4

2020 (37): April 26-30, May 6-7, May 27-29, June 3-4, July 11-13, July 30-August 3, August 13-20, August 24-27, September 4-7, September 17