Understanding the heat of the moment
August 9, 2012
You don’t need a meteorologist to tell you it’s hot out there. But when planning how to cope, it helps to know what some of the weather jargon means.
When the Los Angeles County Department of Public Health declares a “Heat Advisory,” that means that the heat index—a number combining temperature and humidity to approximate what it feels like—has reached 95 or above. A “Heat Alert,” on the other hand, is issued when a heat index of 95 or above is forecast for two or more days. When a Heat Alert is issued, people are advised to take extra precautions and county cooling centers are opened to the public.
The current Heat Alert started Wednesday, August 8, and runs through Sunday, August 12. Affected areas include the San Fernando, San Gabriel, Santa Clarita and Antelope valleys, and Pomona.
The numbers behind the alerts explain a lot about how we feel.
For example, if it is 90 degrees outside with zero humidity, it will feel like 90 degrees. However, at 60 percent humidity, 90 degrees feels like 100 degrees, according to the heat index—and it also comes with the health risks of a 100-degree day. If the humidity were to reach as high as 90 percent during a 90 degree day, it would feel like a blistering 122 degrees.
According to the National Weather Service, we’re currently experiencing unusual humidity because of monsoonal moisture that is being pushed into the region by a complex of thunderstorms in Mexico and a tilted high pressure system over Nevada and New Mexico. In addition to the humidity, this moisture might also bring thunderstorms to L.A. County starting Friday and continuing through Sunday.
The heat itself, even without the humidity, has been historic. On Wednesday, a daily record high of 107 degrees was recorded in Woodland Hills, where today’s forecast calls for 106 degrees. That’s nine degrees above the monthly average, but still well below 119, the record temperature for all of L.A. County, recorded in Woodland Hills in July, 2006.
Coastal areas won’t be feeling the burn nearly as much. Thursday’s highs predicted for Malibu and Santa Monica are just 78 and 83 degrees, respectively—a relative day at the beach. In downtown L.A., the temperature is expected to approach 95 degrees.
Early August’s blazing temperatures come on heels of the hottest month ever recorded in the United States.
From a health and safety perspective, extreme heat should be handled with extreme caution. According to the Red Cross, high temperatures cause more annual fatalities in the U.S. than any other type of weather event. Children, the elderly, the disabled and pets are particularly vulnerable. Heat-related illnesses include heat rash, heat cramps, heat exhaustion and heatstroke—a life-threatening illness that requires immediate medical attention.
The L.A. County Department of Community and Senior Services maintains countywide cooling centers, including three in the San Fernando Valley, at ONEgeneration Senior Enrichment Center, San Fernando Recreation Park and San Fernando Valley Service Center. The department recommends calling ahead to ensure seating is available. The city of L.A. also manages cooling centers at various libraries, recreation centers and senior centers.
The Department of Public Health has a list of “healthy summer” tips for help staying safe in the heat, and additional advice is available online from the Centers for Disease Control and the Red Cross.