While we are going to say goodbye to August on a pretty warm note, we will welcome September in on an even hotter one. Wednesday will bring back a chance of afternoon thunderstorms. An upper level low will keep the flow fairly high which means that the thunderstorms that do develop will move quickly, and any rain from them won’t have much of a chance to douse any fires that start from lightning strikes, so the fire danger is quite high Wednesday. Things should dry out for Thursday and Friday, and temperatures heat up into the low 100s for the weekend.

Sunrise water

So why does it get colder after sunrise? Here’s how it works. Because of radiational cooling, on clear nights the ground gets much colder than the air just a few feet above it. Since thermometers are placed about five feet above the ground, it will show a warmer temperature than the air touching the ground. Once the sun comes up, the sunlight excites the cold air in the first foot or so above the ground (which can be 10 or more degrees colder), which causes it to move around and mix into the next several feet of air. That “mixing upward” drops the temperature of the air at thermometer level.

 

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