The weather station symbols, in the station plot example above, represent the following standard meteorological parameters observed:
Overcast (completely filled-in station circle).
Type of low cloud present.
Type of middle cloud present.
Type of high cloud present.
From the northwest at 15 knots. The long barb is worth 10 knots, while the half barb is 5.
Sea level pressure.
998.7 hPa (hectopascals). Notice that only the last three digits are plotted, and that the decimal point is not.
The sea level pressure is derived from the atmospheric pressure, as measured at the station, to which is added an imaginary column of air (between the station and mean sea level below). It is assumed that this added column of air has the same temperature and moisture characteristics as that of the air observed on the ground.
The change in atmospheric pressure during the 3 hours preceding the observation. In this case, 1.8 hPa (decimal point is not plotted).
The 3 hour pressure tendency. In this case, it was falling at first, but then rose sharply (hence, the "check mark" symbol).
Light snow falling steadily.
Visibility code 66 (16 kilometers)
Minus 10 degrees Celsius.
Dew point temperature.
Minus 12 degrees Celsius.
In the cutout section of a surface analysis map (below), the weather station symbols are analyzed to locate the position of high and low pressure centers.
The analysis of the plotted station symbols also enables us to delimit:
the area covered by cloud (shaded in light brown),
the area of precipitation (shaded in light green),
the type of precipitation in the area is indicated by large twin dots (light rain), large twin commas (light drizzle), twin asterisks (light snow),
the precipitation area shaded in red indicates freezing precipitation (in this case freezing drizzle).
Solid lines - called isobars - are drawn to join points of equal pressure. By convention they are drawn every four hectopascals.
Finally, we can determine that there is a high pressure center of 1034 hPa, located north of Lake Superior, and a low pressure center of 1010 hPa, in southern Pennsylvania, USA.
As you can see, you can learn quite a lot, about the present weather situation, from weather station symbols … once they are plotted on a map, and analyzed.