Excessive Heat in Los Angeles County Valleys, California

The combination of above normal temperatures and relative humidity produced excessive heat across the San Fernando and San Gabriel Valleys with heat index values between 105 and 112 reported.

From the 29th through the 31st, strong high pressure built over the southwest United States. With this pattern, above normal temperatures developed across the mountains and valleys of Southern California. An influx of monsoonal moisture from northern Mexico increased the relative humidity across the area. The combination of very hot temperatures and increased relative humidity produce heat index values between 105 and 112 degrees. The excessive heat resulted in numerous heat-related injuries and deaths. The heat wave extended into the first few days of September.