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The 700 mb map has both temperature and humidity, along with the heights. This map can indicate where there's upward motion occurring and where it's raining (or snowing) or going to rain (or snow). As with the other maps, heights are shown in black. The humidity is in the shading, and isotherms (lines of constant temperature) are in various colors.
The 700 mb level is close to where most precipitation is generated in the atmosphere. If you've got an area where the humidity is very large, it's almost certainly an area where there's upward motion with lots of clouds and precipitation.
Okay, so I've made a big deal about inferring vertical motion from the 500 mb map, and here's another map for vertical motion! Why not just use this one, and ignore the other one?
Actually, there are lots of things that can cause vertical motion, from the significant (upper-level troughs) to the mundane (random ripples in the atmosphere, like waves on the ocean) to the temporary (convective instability). Just looking at the 700 mb map, you can't tell what's causing the upward motion. But in combination with another upper-level map, you can relate the vertical motion to the large-scale motion that's causing it, and pooh-pooh the rest.
In the example above, the high humidity and inferred upward motion over New Jersey is entirely expected: there's a major 500 mb vorticity center just upstream. There's probably downward motion over Ohio and Kentucky, because they are on the other side of the vorticity center (so there's negative vorticity advection), and the humidity is low there. This upward/downward motion pattern can be expected to move with the upper-level system.
On the other hand, over Colorado there was almost no vorticity advection, and yet the relative humidity field suggests that there' upward motion in western Colorado and downward motion in eastern Colorado. Why? Notice the wind direction (remember, the large-scale wind blows parallel to the height contours). The wind's from the west there. That's downslope. The air is going over the Rocky Mountains and descending the lee side. That's why there's both upward and downward motion there. And I would strongly doubt that that area of downward motion is going to be going anywhere, since the Rockies are pretty heavy.
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