Because the system suppresses the down flow of air, it inhibits the formation of clouds, "allowing full solar heating over the Southern California area," he said.
To make matters worse, the offshore airflow that normally moderates temperatures is almost nonexistent. "It's common in the summer to have a low-pressure system over the deserts, and this causes air to blow in from the ocean toward the lower pressure," McKewon said. "This cools off the coast and, to a certain extent, the valleys.
"But the air mass is basically stagnant right now. You're just getting intense heating."
It's Hot, Hot, Hot
While the thermometer hit a record 100 degrees at an Irvine Ranch weather station, the combination of temperature and humidity--measured by the heat index--made it feel hotter. Here is how the temperature recorded this week at WeatherData's Tustin station compares to record highs in previous years:
Humidity Temperature Recorded high (date) Monday 55% 84 97 (Aug. 8, 1950) Tuesday 41% 93 97 (Aug. 9, 1965) Wednesday 35% 94 95 (Aug. 10, 1965) Thursday 28% 98 90 (Aug. 11, 1971) Today* 31% 98 98 (Aug. 12, 1991) Saturday* 25% 94 100 (Aug. 13, 1983) Sunday* 35% 92 97 (Aug. 14, 1983)
* Forecast
Heat Index: Here's How Hot It Feels
The heat index is derived from a formula that involves air temperature, relative humidity and the body's ability to cool itself. For example, today the temperature in Tustin is expected to reach 98 degrees with 31% humidity. That makes you feel as though the temperature is really 101.
Humidity Temperature 90 91 92 93 94 95 96 97 98 99 100 25% 88 89 91 93 94 95 96 97 98 100 102 26% 88 89 91 93 94 95 96 97 98 100 102 27% 88 90 91 93 94 95 96 98 99 101 103 28% 89 90 91 93 94 95 96 98 100 101 103 29% 89 90 91 93 94 95 96 98 100 101 103 30% 90 91 92 94 95 96 97 99 101 102 104 31% 90 91 92 94 95 96 97 99 101 102 104 32% 90 91 93 94 96 97 98 100 102 103 105 33% 90 91 93 94 96 97 99 100 102 104 106 34% 90 91 93 94 96 97 99 100 102 104 106 35% 91 92 94 95 97 98 100 101 103 105 107 36% 91 92 94 95 97 98 100 102 103 106 107 37% 91 93 95 96 98 99 101 102 104 107 108 38% 91 93 95 96 98 99 101 103 105 108 109 39% 91 93 95 96 98 99 101 103 105 109 109 40% 92 94 96 97 99 100 102 104 106 108 110
Source: WeatherData; Researched by APRIL JACKSON / Los Angeles Times
