More than 100 million Americans may endure dangerous heat the next seven days. This current heat wave stretches across 25 states, from California to Maine.
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The heat index, the temperature our body perceives as it tries to cool us, soars well above 100 degrees.
Increasing humidity inhibits our body's ability to cool us. The heat index measures this and tells us the temperature our body really feels.
These extreme hot and humid conditions develop across the Southern Plains, Deep South and from Washington D.C. through Philadelphia to New York City.
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You know who wants no part of this? San Francisco and most of our Bay Area neighborhoods.
We have a unique summer circulation, our free air conditioning, thanks to our cool Pacific Ocean and hot Central Valley.
You will find our coolest conditions and heaviest air closer to the area of origination (Pacific Ocean). The warmest and lightest air develops over the Central Valley.
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Our morning sunshine breaks free from the retreating cloud deck faster from east to west. Earlier sunshine creates warmer ground and rising air. As the hotter and lighter air rises, it creates a vacuum which the cooler and heavier air fills. This turns on our free air conditioning circulation
Unfortunately for those who live closer to the Central Valley, this journey east progressively warms the air as it travels over warmer ground. This creates our average summer spread of 25 from the Coast to Inland.