Four Cities - Overnight Cooling
 

Extreme high temperatures tend to attract the heat-watcher's attention, but overnight cooling is also very important. The National Weather Service has given special attention to weather patterns in which the overnight heat index fails to fall below 80F. When there is a failure of overnight cooling, a variety of adverse events occur: Morning temperatures reach dangerous levels much sooner than usual, the ability of people to cope with heat tends to decrease, and (in the presence of the air stagnation which tends to occur in conjunction with slow-moving air masses) air pollution may increase precipitously.

To explore this issue, profiles of 4 US cities will be presented. This discussion will focus on August 4th. This day has been chosen because major outdoor athletic competitions   are held in these four cities on that date. We will start with San Diego:

San Diego-24-hour day.gif (8682 bytes)

San Diego is the event organizer's dream town. The average daily high never reaches the High Risk Zone. The 4 p.m. heat index is predictable to within 5 degrees! There is reasonable overnight cooling, but it really doesn't matter. From the standpoint of heat stress, San Diego on August 4th is an ideal choice.

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