Pat Shingleton: "Peak Heat..."
The National Climatic Data Center analyzed climate data from 1981 to 2010 and constructed a map depicting the peak summer heat. Most locations will experience a lot more summer weather and haven't experienced their warmest day of the year. For the southwest, the warmest weather traditionally occurs before the end of June. Phoenix and Tucson report average highs at or near 100 degrees throughout the summer. For our area, high heat and humidity assist in activating convective showers that drop our daytime highs by 15 degrees. Along the West Coast, the summer peak doesn't kick-in until fall. Inland air heats and rises over the top of cool, dense air that hugs the coast. This causes an inversion that traps the chill on California's coast.