What factors make one sunny day so much warmer than another?
Our hottest days come when there's a surge of hot, dry air that moves from the interior valley of California into Puget Sound. It moves in a 'thermal' trough of warm, low pressure air. Such hot weather is amplified when winds move downslope off the Cascades into the Puget Sound area. That happens when the 'thermal trough' lines up along the coast with higher pressure east of the Cascades. These downslope winds warm as they sink and compress or 'squeeze' while sliding down the west slopes of the Cascades toward Puget Sound.