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Heat Watch | CLIMAS

 SW Climate Outlook

Heat Watch

Heat Watch

In typical summer fashion, temperatures have ramped up across the Southwest U.S. and northern Mexico over the past month. Several cities along the Rio Grande have experienced multiple heat waves and have set high temperature records. In mid-May, a heat wave in Laredo set records on four consecutive days, with temperatures ranging from 100-104 °F from May 15-18. A similar heat wave in Del Rio, TX on May 26-29, when temperatures ranged from 103-106 °F, set records on 3 of 4 days. Brownsville, TX also set record highs on May 25-26 with temperatures reaching 97 °F. Then, in early June, a heat wave broke records along the entire border reaching all the way from Brownsville to El Paso. Both Laredo and Brownsville set new high temperature records on 6 consecutive days, from June 1-6, with temperatures ranging from 105-108 °F in Laredo and 97-98 °F in Brownsville. El Paso set records on May 31 and June 2, with temperatures of 102 °F and 106 °F, respectively. Further into June, Santa Fe set records on June 12 and 14, with temperatures of 97 °F and 95 °F, respectively. Looking forward, forecasts indicate that temperatures will be above-average over the next month for Texas (Figure 5).

In Mexico, the highest temperatures recorded in the most populated cities across Northwest Mexico were 113 °F (45 °C) in Mexicali on June 12; 111.2 °F (44 °C) in Hermosillo and Ciudad Obregón, Sonora, on June 4 and 12, respectively. Ciudad Juárez, Chihuahua reached 105.8 °F (41 °C) on June 11-12, Culiacán, Sinaloa reached 104.9 °F (40.5 °C) on June 2, and Chihuahua, Chihuahua reached 104 °F (40 °C) on May 30. None of these temperatures broke previous records.

A new heat forecasting tool produced by the U.S. National Weather Service provides additional insight into near future temperatures. HeatRisk is an experimental forecasting tool that visualizes heat risk potential one-week in advance (Figure 11). It is designed to provide guidance to decision makers and heat-sensitive populations (such as outdoor workers and those with young children) on when to take action in preparation of a heat event. Each color category shown in the map represents a different population that is at risk. For example, yellow is a low-level of risk and means that those who are extremely sensitive to heat should take action to prevent illness. When the highest level (magenta) is forecasted, the entire population is at risk, due to long-duration heat with little to no relief overnight. HeatRisk can be accessed from the National Weather Service page for most cities (

Figure 11 (right): Screenshot of NWS HeatRisk for July 4. The table (right) describes the meaning of each color.

Extreme heat causes the most deaths in the U.S. of any weather-related disaster. During this time of year in the Southwest U.S. and northern Mexico, prior to the start of the North American monsoon, it is particularly important to be prepared for the unrelenting heat. Populations at increased risk of heat-related illness include children, pregnant women, elderly, those taking medications, those working outdoors, those with disabilities, those without adequate cooling, and the socially isolated. Be sure to check on loved ones and neighbors and call 911 if anyone is experiencing symptoms of heat stroke (e.g., headache, fast pulse, confusion, nausea, loss of consciousness). For more information on vulnerable populations, the symptoms of heat-related illness, and what to do to prepare, visit the CDC extreme heat webpage (en Espanol: