Under Pressure

January 22, 2015: Tomorrow (Friday, the 23rd), a large area of high pressure should help clear the sky out and give us some sunshine after a 2-day gloomy stretch.  You may have heard this plenty of times before, that high pressure can provide fair or quiet and clear weather. So how does this all work?

An area of high pressure promotes downward movement in the atmosphere. The sinking motion in the atmosphere is caused by the build up of air within that area, causing the air within the high to be more dense or heavier than the air around it, so it starts sinking.

High atmospheric pressure causes sinking within the atmosphere, clearing the sky out.

High atmospheric pressure causes sinking within the atmosphere, clearing the sky out.

If you think back to your lessons about the water cycle, when we heat air up with the sun, it becomes less dense, starts rising into the atmosphere, where the water vapor within the air cools, condenses, and starts to form clouds and rain.  The exact opposite occurs within an area of high pressure.  The sinking air compresses on its way down, causing the air to warm, and dry out. Without any moisture left and an overall sinking motion in the atmosphere, clouds aren’t able to form, and we have generally sunny, quiet weather with light winds.

Of course, this is an idealized situation, so this may not happen every time an area of high pressure moves in, but when we do talk about high pressure in the forecast, you now know why we generally talk about clear, calm weather as the high moves in.

– Alex

Share

Posted under weather

This post was written by Alex Kirchner on January 22, 2015

Leave a Comment

Name (required)

Email (required)

Website

Comments

 

More Blog Post

Previous Post: