In other words, the 500 mb height at any point on the map tells us about the average air temperature in the vertical column of air between the ground surface and the 500 mb height plotted at that point. The height pattern tells us where the air is relatively cold and where it is relatively warm (see 500 mb side view.)

This is an important parameter to meteorologists because it is in the middle of the atmosphere. The 500mb height is the height at which the pressure is 500mb. When the 500mb height is low, there is low pressure at the surface, and when the 500mb height is high, there is high pressure at the surface.

The 1000-500 mb thickness value of 540 (5,400 meters) is the traditional line to determine rain verses snow. The 540-contour closely follows the surface freezing temperature (32°F/0°C). The 540-thickness line (5,400 meters deep) is approximately the point where precipitation changes from liquid to frozen or vice versa.

9,100 meters
An air pressure of 300 millibars is said to occur near 30,000 feet (9,100 meters) in elevation. But the height ranges from near 27,000 to 32,000 feet (8,200 to 9,600 meters). For the heights of each 300 mb contour the last digit, 0 (zero), is omitted from the chart.

500mb Geopotential Height and Vorticity Black contours indicate the geopotential height of the 500 millibar surface, in tens of meters. Low geopotential height (compared to other locations at the same latitude) indicates the presence of a storm or trough at mid-troposphere levels.

approximately 5,500 meters
The 500 mb chart represents weather conditions in the mid- troposphere, at a level where approximately half the mass of the atmosphere lies below this level. This level is at an altitude of approximately 5,500 meters (18.000 ft).

Winds at the 500-mb level are generally not the actual jet stream, which is generally between 200 and 300 mb. Jet streams exist due to horizontal temperature contrasts. In an extremely cold atmosphere, the Arctic jet stream can extend down to 500 mb.

around 5.5 km
500 hPa Geopotential Height On average this level is around 5.5 km above sea level, and it is often referred to as a steering level, because the weather systems beneath, near to the Earth’s surface, roughly move in the same direction as the winds at the 500 hPa level.

For example, if a station reports that the 500 mb [i.e. millibar] height at its location is 5600 m, it means that the level of the atmosphere over that station at which the atmospheric pressure is 500 mb is 5600 meters above sea level. This is an estimated height based on temperature and pressure data.”

5,000 feet
This pressure level is near an elevation of 5,000 feet though it ranges from 3,800 feet (1,170 meters) to 5,200 feet (1,590 meters).

500mb Geopotential Height and Vorticity Black contours indicate the geopotential height of the 500 millibar surface, in tens of meters. Negative (positive in SH) vorticity is associated with calm weather, and will tend to coincide with ridges in the geopotential height field.

Above (or generally north) of the line the 500 mb heights are lower than 5700 meters and below (or generally south) of the line the 500 mb heights are higher than 5700 meters. I expect that you can determine the 500 mb height at any point on a map like this.

This is nice when looking at computer-generated (predicted) forecast maps of the 500 mb height pattern, as it tells us what the computer model predicts the future weather to be. By the way all weather forecasting today relies on computer models.

It is based upon the assumption 500 mb is one-half of 1000 millibars (at sea level) and the top of the atmosphere, zero millibars, which occurs at 30+ miles (50+ kilometers) high. For the 500 mb level constant pressure chart heights, the last digit, 0 (zero), is omitted from the chart.

With experience one can easily visualize the large-scale weather pattern by looking at the 500 mb height pattern. This is nice when looking at computer-generated (predicted) forecast maps of the 500 mb height pattern, as it tells us what the computer model predicts the future weather to be.