The Heat Wave Of The Central United States
So why is there so much heat and humidity rising up into the Northern Plains creating a surge of hot weather? The answer is in the weather map above.
If we look over Lake Michigan we see an area of High pressure which has a clockwise flow over the region.
So places on the East are having cooler weather as they are getting the air from Canada pushing down towards them. North Dakota into the Gulf Coast are on the back side of the high so there air is coming from the Gulf of Mexico.
If we recall the air from the Gulf of Mexico is Marine time Tropical air. So as the air leaves the Gulf and starts to move over the land the moisture decreases, however the heat does not.
For example along the MS Gulf Coast the temps today will be 97F with 80-85% Relative Humidity which makes for a very hot and humid day, while in Nebraska the temp might go into the 100’s however the moisture will be lower as it’s further away from the Gulf their humidity might only be 60-65%. Now you know why the heat wave is on.