We continue our discussion on the 700 mb pressure level. At this level we are closer to Earth’s surface, but still remain about 10,000 feet above. Some of the world’s tallest mountains peak are at these levels — if not higher.

There are several weather features plotted on a 700 mb map. Relative humidity, Omega (we’ll discuss more), and height contours. Temperatures and winds may also be presented.

The biggest factor on this map will show Omega. This is referred to as the upward or downward motion in the atmosphere. Or also known as rising or sinking air.

Omega is vertical motion.

Heights and Omega

If rising air is present then rain is probably likely since the vertical motion will lead to a change in the weather. If it is sinking then you can expect nicer weather.

Since this chart is lower in the atmosphere the troughs and ridges that we observed from the 500 mb map are more defined here. This is shown in the picture above. Notice the big dip in the western U.S., that is a trough.

Around the troughs are also areas of ascent and subsidence.

Relative humidity is also plotted because at 700 mb this is the height at which clouds develop. And it’s easy to say because with more humidity in the sky then the higher the possibility of clouds. If the humidity is low then sunnier skies. Of course, it does all depend on what other weather features are present.

If there’s ascent and high humidity all at the same time then clouds are practically a given.

Height contours and relative humidity.

As you can see each level so far has different characteristics and each one tells a different part of the weather story. When they are all combined meteorologists can get a fairly accurate weather forecast.

My goal is to teach people the weather and the science behind a forecast. We are discussing each level specifically and what it entails in the simple form. My versions are simplified so that almost anyone can understand. There are many more ways to discuss each plot and more discussions will come to follow, but please feel free to comment any question you may have below and I will get back to you with an answer.

We will continue to talk about more levels of the atmosphere. The next one is the 850 mb.