Skies are clear from the the Mississippi Valley to the slopes of the Rockies with hardly a cloud to be found throughout the Plains states early this week. But how does such a large area clear out and what is behind this nice weather?
Consider an area of high pressure, similar to the one that has built in from Canada into the Central Plains this week. It is right in the middle of a large area of sinking air. (See the blog entry “What are disturbances?” for more about this process)
At the ground, this sinking air then spreads out allowing even more air to sinking down from above.
What happens as the air sinks is that it warms. Just like being high up in the mountains it gets colder, as air sinking lower in elevation air warms up. That doesn’t necessarily make it hot at the ground, but the air itself is warmer than it used to be. That lowers the relative humidity since the relative humidity is a measurement of how much humidity is in the air based on what the current temperature is. The end result is no cloud cover.
So if you are enjoying this clear weather, then thank this large high pressure that has pushed south into the Plains this week!