KSHB 41 Weather Blog | Heat Wave Day 3 to dense fog across Kansas City

Posted at 8:23 AM, Aug 21, 2023
and last updated 2023-08-21 10:35:26-04

KANSAS CITY, Mo. — Good Monday bloggers,

There is much going on with the weather as we are tracking the heat wave, dense fog, an active tropics and our next cold front.

First, heat waves and dense fog are not usually associated with each other. But, in this case they are together. Fog forms when the temperature cools to and below the dewpoint and the humidity rises to 100%.

If the temperature is 80° and the dew point is 50°, the humidity is 35%. This means the air is filled with 35% of water vapor. It can hold 65% more, so the air is fairly dry. If the temperature is 80° and the dewpoint is 80°, the humidity is 100%. This means the air can not hold any more water vapor. If the temperature cools when the humidity is 100%, then fog can form as the moisture has to condense out, because the air can not hold any more water vapor at 100%. So, a cloud or dew forms. Hence, the name dewpoint. I hope this makes sense.

So, this morning around 6 AM we had temperatures 77°-80°.


Dewpoints were 75° to 79°.


This means there were many locations with humidity between 97% and 100%.


This lead to areas of dense fog due to the light wind as the moisture condenses out where there is cooling below the dewpoint. Your windows may be fogged up as well. This is because if your house or car is cooled to 70° with the AC, it is cooling the air just outside your house to below the dewpoint, so the water condenses out on your window.

The dense fog was mostly around KC this morning. This setup will continue Tuesday and Wednesday mornings. The fog may make to all of KC these mornings.


Now, warm air can hold more water. So, 100% humidity at 50° has much less water vapor in it than 100% humidity at 80°. Even though both airmasses are saturated.

Sunday at 2:25 PM it was 102° in Lawrence with a dewpoint of 84°. The humidity was 57%. But, when 102° air is 57% saturated that means there is a lot of water in the air. Our sweat does not evaporate enough to cool us, so the heat index rose to an incredible 134°. The heat index was 134° several times in Lawrence on Sunday. The heat index peaked at 121°at KCI several times over the weekend.


Now, all that being said. It is HOT! We need a cold front. There is one showing up and the 5 minute video below details it's arrival and also a more active tropics.

Could a tropical system bring our next rain?

Have a great week
Stay cool, stay healthy